Components of the feeding niches of Geocoris spp. (Hemiptera: Lygaeidae)


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Components of the feeding niches of Geocoris spp. (Hemiptera: Lygaeidae)
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Crocker, Robert Lemuel, 1945-
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Table of Contents
    Title Page
        Page i
        Page ii
        Page iii
        Page iv
    Table of Contents
        Page v
    List of Tables
        Page vi
        Page vii
    List of Illustrations
        Page viii
        Page ix
        Page x
    I. Components of the natural feeding niches of Geocoris spp.
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
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        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
    II. Differential importance of the eyes and antennae in the capture of motile and immotile prey by Geocoris punctipes
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
    III. Gross internal morphology of a predatory lygaeid, Geocoris punctipes
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
    IV. Summary and conclusions
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
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        Page 86
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        Page 96
        Page 97
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        Page 101
        Page 102
        Page 103
        Page 104
        Page 105
        Page 106
        Page 107
        Page 108
    Biographical sketch
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
Full Text







This dissertation is dedicated to my wife, Ann,

whose love, advice, and encouragement have sustained me

throughout. She is the unsigned second author to this



I am very grateful to my chairman, Dr. W. H.

Whitcomb, and committee members, Drs. C. A. Lanciani,

N. C. Leppla, and T. J. Walker, for assistance and guidance

throughout my program. Other faculty members whose council

has been invaluable are Drs. D. H. Habeck, S. H. Kerr,

J. L. Lloyd, and R. I. Sailer.

My research could not have been accomplished

without the aid of the Florida Division of Plant Industry,

the University of Florida, and the U.S. National Museum in

the taxonomic determination of specimens; I am deeply in-

debted to the following taxonomic experts: Drs. W. F. Buren,

G. W. Dekle, H. A. Denmark, G. B. Edwards, R. Godfrey,

E. E. Grissell, D. H. Habeck, David W. Hall, A. B. Hamon,

R. L. Hoffman, L. P. Kish, K. Langdon, W. N. Mathis, F. W.

Mead, D. R. Miller, S. Nakahara, J. C. E. Nickerson,

K. O'Neill, W. B. Peck, D. B. Richman, R. I. Sailer, H. V.

Weems, W. W. Wirth, D. P. Wojick, R. E. Woodruff, and D. L.

Wray. I also wish to acknowledge Mrs. T. Green, Mrs. E.

Mercer, Mrs. D. O'Berry, and other technical and staff

personnel of the Florida Division of Plant Industry for

their roles in processing my specimens (all persons being

listed alphabetically).


For critical review of all or of portions of the

manuscript, I am grateful to my committee members, and to

Drs. G. B. Edwards, David W. Hall, Donald W. Hall, R. C.

Hemenway, S. H. Kerr, J. L. Lloyd, J. L. Nation, and

R. I. Sailer (all of the University of Florida), and

Drs. G. F. Knowlton (University of Utah) and C. Lincoln

(University of Arkansas).

The design and statistical analysis of portions of

my research were greatly assisted by Dr. R. C. Littell and

Mr. W. W. Offen (Statistics Unit, Institute of Food and

Agricultural Sciences, University of Florida).

I am thankful for the financial support for this

research, which funds came from the National Science Foun-

dation and the Environmental Protection Agency, through a

grant (NSFGB-34718, later known as BMS 75-04223), to the

University of California. The findings, opinions, and

recommendations expressed in this dissertation are my own,

and not necessarily those of the University of California,

the National Science Foundation, or the Environmental Pro-

tection Agency.

Finally, I acknowledge my family and friends; the

value of their encouragement and assistance over the years

cannot be measured. I especially thank my wife, Ann, and

our children Sonia and Paul for their long-suffering pa-

tience, and for having faith in me. I also appreciate the

encouragement received from my parents and from Ann's parents.



ACKNOWLEDGMENTS . . . . . . . . .. iii

LIST OF TABLES . . . . . . . . .. vi

LIST OF FIGURES . . . . . . . . .. viii

ABSTRACT . . . . . . . . . . .. ix



Introduction . . . . . . 1
Materials and Methods . . . . 6
Results and Discussion . . . . 7

Predation . . . . . . 7
Phytophagy . . . . . .. 42
Necrophagy . . . . . . 50

PUNCTIPES . . . . . . .. .. .. 55

Introduction . . . . . . .. 55
Materials and Methods . . . .. 56
Results and Discussion . . . .. 58


Introduction . ................. 62
Results and Discussion ........... 64


REFERENCES . . . . . . . . . .. 74

Supplemental Bibliograpy . . . . .. 82

BIOGRAPHICAL SKETCH . . . . . . . .. 109



Table Page

1. Arthropods reported on the basis of
direct evidence as natural prey of
Geocoris spp. of the world . . . . 9

2. Arthropods found in the present re-
search to be natural prey of Geocoris
spp. in Florida . . . . . . .. 14

3. Arthropods unsuccessfully attacked by
Geocoris spp. in nature in the present
research in Florida . . . . . .. 19

4. Lengths of target and actual prey
of Geocoris spp . . . . . . ... 24

5. X2 analysis of the relationship between
the use of defensive behavior by the
prey and the outcome of an attack by a
Geocoris (3 species pooled), with the
defense coming (A) prior to contact,
and (B) following contact between
predator and target prey. Data=numbers
of attacks with the specified prey
behavior and outcome . . . . . .. 30

6. Natural foodplants of Geocoris bullatus
in Florida .. . . ... .. . . . . 34

7. Natural foodplants of Geocoris puncti-
pes in Florida .. . .. . . . . ... 43

8. Natural foodplants of Geocoris uligi-
nosus in Florida . . . . . . .. 44

9. Dead animal matter fed on by Geocoris
bullatus in Florida . . . . . .. 52

10. Dead animal matter fed on by Geocoris
punctipes in Florida . . ........... . 53

Table Page

11. Dead animal matter fed on by Geocoris
uliginosus in Florida . . . . . .. 54

12. Mean numbers (x) of eggs and of newly
hatched larvae of Trichoplusia ni
consumed daily by intact and by altered
(antenna-less) adult, male Geocoris
punctipes at 25C under 14hL:!0hD vs.
nearly continuous darkness. Each mean
based on 6 observations of 10 individual
predators (=60 observations) . . . .. 59

13. Analysis of serial, horizontal sections
of an adult, male Geocoris punctipes ... .. 65


Figure Page

1. Lengths of flighted prey of Geocoris
spp. plotted against the lengths
of Geocoris . . . . . . . .. 26

2. Lengths of sessile prey of Geocoris
spp. plotted against the lengths of
the Geocoris . . . . . . . .. 27

3. Lengths of ambulatory prey of Geocoris
spp. plotted against the lengths of
the Geocoris . . . . . . . .. 28

4. Lengths of saltatory prey of Geocoris
spp. plotted against the lengths of
the Geocoris . . . . . . . . 29

5. Atmospheric saturation deficits at
which phytophagy by Geocoris spp.
occurred at various temperatures
in Florida . . . . . . . .. 49

6. A composite, semi-diagrammatic
representation of the major internal
organs of an adult male Geocoris
punctipes . . . . . . . .. 66

7. Digestive tract of Geocoris punctipes . . 67

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



Robert Lemuel Crocker

December 1977

Chairman: W. H. Whitcomb
Major Department: Entomology and Nematology

The feeding niches of Geocoris bullatus (Say),

G. punctipes (Say), and G. uliginosus (Say) (Hemiptera:

Lygaeidae) were investigated under natural conditions, and

were found to be quite broad. I found that these Geocoris

spp. prey upon members of at least 56 species, representing

3 classes of arthropods. Many of their prey are agricul-

tural pests. The observed lengths of field prey of adult

Geocoris ranged from less than 0.5 mm to greater than 8

mm; both motile and immotile stages were attacked. In

the field and in the laboratory, Geocoris often were able

to take a prey without triggering the prey's defensive

behavior. Although specimens of G. punctipes were able to

find motile prey (small larvae) in the laboratory using

either their eyes or their antennae, their antennae were

necessary to find immotile prey (insect eggs).

These Geocoris spp. were found to be primarily

predaceous, but they also fed to a limited extent on

members of several families of herbaceous angiosperms in

nature, without harming the plants. They fed on vegetative

structures and to a lesser extent on seeds. These Geocoris

spp. occasionally were observed to feed on dead insects

in nature; such food probably is not usually prominent in

their diet.

The eyes and optic lobes of G. punctipes are well-

developed, as would be expected in a highly visual hunter.

The ventriculus lacks gastric cecae, a trait associated

with predatory and omnivorous bugs; most other lygaeids

are phytophagous and have gastric cecae.

The abundance of Geocoris spp. in many agricultural

habitats and the breadth of their feeding niches (their

prey include many resurgence pests) indicate that these

entomophages are probably of great importance in preventing

pest outbreaks.




Geocoris spp. are generally considered to be among

the most important predators in cotton, alfalfa, soybeans,

strawberries, turfgrasses, peanuts, and many other crops.

This is doubly interesting, because most lygaeids are

phytophagous, and some--such as the chinch bugs (Blissus

spp.)-are serious pests. That Geocoris should hold such

a reputation is due primarily to their abundance, and is

backed up only by scattered observations of predation; their

natural feeding habits have never been studied systemati-

cally, except in reference to a few target pests.

I felt that although there is considerable prag-

matic value in knowing the natural enemies of our key pests,

such an approach tended to give a distorted view of the

niche of the entomophage--especially if that entomophage

were polyphagous. In order to gain a more balanced per-

spective of the roles and importance of Geocoris, I began

observing in detail the behavior of individuals of each of

the Florida species (G. bullatus (Say), G. punctipes (Say),

and G. ulic;inosus (Say)) in a wide variety of their natural

habitats, both wild and cultivated. From that field work,

it soon became apparent that the natural feeding niche of

Geocoris spp. was quite broad, including predation, phyto-

phagy, and necrophagy.

Most previous research into the prey of Geocoris

spp. was conducted in the laboratory or in field-cages,

and primarily involved the ability of Geocoris to feed on

or control 1 or a few target species (Barry et al. 1974;

Butler 1966, 1967; Clancy and Pierce 1966; Dunbar and Bacon

1972; Ewing and Ivy 1943; Goeden and Ricker 1967; Goodarzy

and Davis 1958; Irwin et al. 1974; Leigh and Gonzalez 1976;

Lingren et al. 1968; Lopez et al. 1976; McGregor and

McDonough 1917; Nielson and Henderson 1959; Orphanides et

al. 1971; Tamaki and Weeks 1972a,b; van den Bosch et al.

1969; Waddill and Shepard 1974; and York 1944). Although

such work has indicative value, it usually makes only

limited demands upon the predator's searching ability,

offers little if any choice in prey, may not involve the

developmental stage or stages the predator would normally

attack, and usually deprives the predator, its prey, or

both of normal environmental clues or behavioral options

that might affect the outcome. Even though polyphagous

or even oligophagous predators might reasonably be ex-

pected to gain a balanced diet by feeding on diverse but

individually inadequate prey types, survival and reproduc-

tion on enforced, narrow diets are commonly used as indices

of the normal dietary importance of the item. Notwithstand-

ing these limitations, some such work has been incisive,

e.g., that of York (1944), which indicated that Geocoris

spp. appeared suited to making their living by predation

supplemented by phytophagy and necrophagy.

Lincoln et al. (1967), Whitcomb (1967) and Buschman

et al. (1977) avoided many of the previously mentioned

problems of laboratory and field-cage experimentation by

using naturalistic settings in the field. Plants that had

been enriched with target prey were observed to detect

predation by naturally occurring predators. These studies

indicated that G. punctipes is a predator of eggs (Lincoln

et al. 1967) and small larvae (Whitcomb 1967) of the boll-

worm, Heliothis zea (Boddie) and of larvae of the velvetbean

caterpillar, Anticarsia gemmatalis (Hibner) (Buschman et al.


Inferences of predator-prey relationships from

comparisons of the population dynamics of the candidate

predator and prey are complicated by the possibility

(1) that the abundance of members of either or both of the

candidate taxa is regulated by an unconsidered factor or

factors, (2) that opposing influences may negate each

other, resulting in no net change in 1 of the populations,

(3) that mortality which is insignificant in one context

may be quite important under different conditions, and

(4) that unless adequate allowance is made for the predator's

generation time, any numerical response will depend on the

net rate of migration, which is itself dependent on many

factors. Considering these complications, the conclusions

of Ehler et al. (1973), Oatman and McMurtry (1966), Menke

and Green (1976), and Staten (1970) concerning correlations

between Geocoris spp. and particular target prey should be

viewed as tentative pending further verification. Nickel

(1958) found a positive correlation between damage by the

bollworm and the abundance of G. ventralis Fieber in Para-

guayan cotton and strengthened the argument that this was

due to a predator-prey relationship by tying that mathemati-

cal correlation to the tremendous disappearance rate of

eggs and young larvae of the bollworm. In an outstanding

combination of mathematical and observational techniques,

Tamaki (1972) demonstrated that G. bullatus responded

numerically (by immigration) to the green peach aphid, Mvzus

persicae (Sulzer), and inflicted 58 percent mortality upon

individuals returning to peach trees after having fallen

to the earth on leaves in the autumn.

Van den Bosch and Hagen (1966) stated that Geocoris

take moisture from the cotton plant, but that this behavior

appears to be harmless to the plant (whether these are

field or laboratory data is unclear). Existing laboratory

evidence indicates that phytophagy by Geocoris, in fact,

does not harm the plants (Dunbar 1971, King and Cook 1932)

and that it provides the Geocoris with supplemental moisture

(York 1944). Stoner (1970) demonstrated that nymphs and

adults of G. punctipes can obtain not only moisture but

also nourishment from some plants, although prey are

necessary for normal longevity and fecundity. Stoner ob-

served that these phytophagous habits might allow improved

survival when prey are scarce. Dunbar and Bacon (1972)

discovered that reproduction by G. punctipes in the

laboratory was greater when plants were included in the

diet than when prey were the only food. Ridgway and Jones

(1968) discovered that phytophagous feeding made G. pallens

St&l vulnerable to systemic pesticides under laboratory

conditions. Until the present, however, there have been no

clear references to natural phytophagy by Geocoris spp.

Necrophagy by Geocoris spp. has received little

attention. York (1944) demonstrated that caged specimens

of G. pallens and G. punctipes survived equally well on

either live or dead insects, but that plants had to be

included in either diet. Dead insects from which the fat

had been extracted were less capable of sustaining Geocoris

spp. than were frozen or air-dried specimens. York con-

cluded that Geocoris spp. preferred live to dead prey,

because the presence of insect corpses did not affect the

number of live beet leafhoppers consumed. Knowlton (1940)

noted that G. decoratus Uhler "has been observed to feed

. . upon dead Lyqus elisus and L. hesperus;" this

apparently is the only previous record of natural necrophagy

by Geocoris. Coprophagy by Geocoris has not been reported


Materials and Methods

Observations were made throughout most of the year

on naturally occurring Geocoris under unmodified field

conditions. Once a Geocoris was selected for study, it was

kept under continuous watch for periods of up to ca 2 h,

during which time the researcher remained as unobtrusive as

possible. The basic criterion of feeding was that a

Geocoris stuck its beak into an insect or a plant for

several sec. Penetration was confirmed (1) by observing

the flexure which occurs at the joints of the labium when a

bug's maxillary and mandibular stylets are inserted into

tissue, or (2) by seeing the bug manipulate the prey by use

of its beak. Athletic knee and elbow pads were necessary

to protect the observer from sharp objects (such as sand-

spurs and rocks) on the soil, and made possible protracted

periods of motionlessness.

Previous laboratory (Crocker et al. 1975) and

field experience showed that adult female Geocoris consume

much more food than do adult males. For that reason, I

spent the majority of my time observing adult females in

order to maximize my return. Because it is difficult under

field conditions to discern whether or not a small nymph

is actually feeding, I watched only adults and a few mid-to-

late instar nymphs.

I observed Geocoris in the following habitats in

northern and central Florida: (1) fallow agricultural land

with Oenothera laciniata Hill, Gnaphalium purpurium L. and

miscellaneous other old-field weeds; (2) white, sandy soil

with sparse, weedy vegetation including mainly wild Cynodon

dactylon (L.) Persoon, Diodia teres Walter, and Panicum

lancearium Trunius; (3) clay fill-dirt with low growth of

C. dactylon, Digitaria adscendens (Hbk.) Hendr., Eleusine

indica (L.) Gaertner and other weeds; (4) sandy soil with

no-pesticide vegetable garden surrounded by wild C. dacty-

lon, Richardia scabra L., and other weeds; (5) sandy soil

with small no-pesticide field of Glycene max (L.) Merrill

infested with Cassia obtusifolia L.; wild grasses including

Dactyloctenium aegyptium (L.) Beauvois bordering the field;

(6) sandy loam soil with Trifolium incarnatum L. under pecan

trees; (7) residential garden with Fragaria ananassa

Duchesne on pine straw mulch.

Results and Discussion


Previous to the present research, there were for

Geocoris bullatus, G. punctipes, and G. uliginosis, respec-

tively, 2, 10, and 3 species of known natural prey (plus

2-3 references to Geocoris sp. or spp. which almost

certainly refer to 1 or more of these species of Geocoris);

these known prey represented 8 families divided among 4

orders of insects (Table 1). Among 117 observations, I

have found an additional 17, 11, and 23 natural prey species

for those respective Geocoris spp., and have confirmed that

Orius insidiosus (Say) is a natural prey of G. punctipes

and G. uliginosus; the 56 taxa presently known to be prey

of these Geocoris spp. are from 3 classes, 10 orders, and

30 families of arthropods (Tables 1, 2). Additionally,

I have witnessed 23 unsuccessful attacks involving 16 target

species, 2 of which are known to be prey, and the others of

which are probably prey (these probable prey represent an

additional 1 order and 3 families) (Table 3). Only 19 prey

species are known for the other ca 125 species of Geocoris

in the world; the majority of these records are found in

numerous publications by Knowlton (Table 1), and involve

primarily G. decoratus Uhler, which occurs in the western

United States. With 2 exceptions, the 3 presently studied

Geocoris spp. are known to take prey from all arthropod

families preyed on by other members of their genus (Tables

1, 2).

The breadth and considerable overlap among types of

prey taken by Geocoris spp. indicate that which of the local

species of Geocoris dominates any particular site probably

depends on factors other than what prey are present. There



(D-noted by 2-lettiC Abbreviation)

rei l 1 1 1 g i

Prey Habstat Local Seleresca .1 61 "1 III 0 I 5 1 tl ;Il J I J I ;l 4 l


Acar n3


Illts tI


A l5.IybErd


t oacco flea beetle

It. I ,rse.nid

Indial Chertian (1933)

on orange North
tree Tranvaal

Hease. (1947)

tobacco Ga. ChamberlIn
and Tunket

tobacco Va. DOmi.ick (1943)

India Satraja
.C a). (1964)


MIaLpt..C rldae

Orics .,.

0. inSidl-us (Say)

0. tristlcolr (White)
m1r005 pb-'t. bug


HyTu, crcae (Schillinq)
f~il clhncli bug

N. eric0e, nymph


.1r-d namphs

6ll~cc raprid..S

rcpcd plant bug

Cli-lig ( Ang-satUS
Z;-Cl ry

CrEontlades rallidu.
P.1cc~u, nyny'hs

~2rso knight

tarnished plant bug

L. ..aten l- (L.)

i. Mots .er

cotton Calif. van den Bosch
et .1. (195b)

cotton Ark. Wlitcomb and
oeil (1964)

cotton Ark. Whltcomb and
Bell (19641

Utah Knowlton (1935)

Utah Knowlton (1933. 1936)

cotton Miss. Caopbell and
Hutchins (1952)

Ark. Isely (1927)


cotton Egypt

alfalfa Arit. &

Ranqaraljn et
al. (1964)

Soyer (1942)

Stitt (1940)

Arxz. Chaplain and
Shoildt (1967)

cotton AXk. Whitcomb and
Bell (1964)

Isely (1927)

.ePelly (1932)


pa cli

Pa 61



TABtLE l--Co tinued

(Denoted by 2-1etter Abbreviataon)

-I 2

3 8 81 8! -3 81 ,
0 04~c e o -lf U i il

Prey Habitat Local Wareen 1 0l 01 ;1 1 u;1 1 1 61 61 01 6C

P- atto Arks. Whire oob and app
siriB iRtuoer) ell 119641

1oco tleahopper,
lIt or 2nd -nstar



T7i0, 1creodes ,abtilonea

(Hii~n .00. LgVla
binded ifi white fly,
3rd & 4th instar
and pupje

T, ebLt loneA

7. e rt, lnea,
larve & pupae



an pretoua

0. trdic.rairA5 Koch,
a ture apoterua

m hacre esiClantl i
xo, [tee

cotton and


n o,', -tus

Warh. Landia at al.

I1l. Dysart (1966)

La. Watve and Clover

Wash. KnowIton (1947)

Utah Knowlton (1944)

Ore. Knowlton (1947)

P. W. (Ialtenbach)

9. fii
inc. 20., 3rd infltar

-. zt-lJ6un Knowlton,
an aP-tero,- dult
-I a I-q" nymph

Ht5y-s Lrsicae (Sulzer),
gr-n ach aphid

9. Ees~a



CirculL'er tonel lug

nyn- d ad.11.
4-1. Wi

C.tenruelljs O9'ez),
-et ledthopper

_ia'.s:4 dena'.nr instant
co-ton le.fnopper

!" iL-!^ (Desl.o9)
F. sd-nci (O..LnO(.


Fe, nlnic niLr.n8c (Cckh.rll),
.triped -eccybcq


on soll


on soil,
peach trea

Utah Krolton (1949)

Utah Knolton (11944, 1947)1
KncLton et al. (1938)

Utah nowltmon (1947)

Wash. TacakL (1972)

Cah. Taaki and W4ek$ (1972)

Utah Knowlton (1940)

uqar beat, Utah

Kno-lton (1933.2, 1936,
1937, 1940. 1944, 1947)

Calif. Esmig (1926)

Indl. Subha Rtao at al.

Calif. Hoffitt (1967)

Ark. Ocely (1927)

Phillipplnes Otn.. and BU0ca (1935)


TABLE L-Contin-d

(Denoted by 2-letter Abbreviation)

Pray Habitat Locel Rfarranc. o0 "1 "I 1 1 "1 ;1 0) 0 0 1 ;1 .1


P.r-trsion cckerlli potato Utah Knowlton (1933) d.
yotato psyllhd

Trioza ,uoa Foster. Salix p. Utah Knowlton (1942) at
4th inntar nymph



Hlaotlh-V'. p., tobacco od S.C. N.uzig (196S) pu
early insata ilntaoe otton

H. eM (Boddie), oottm Ark. e a). (1967) pu

Taxon & Stage* of





Prey 1 0 0


Acari, undet.

Oribato:, undet.

Liacaridae, undet. (imm)

Mesostio;mata, undet. (1st n)


AplonObli sp.
(jpidor mite)

Petrobia apicalis (Banks
(a spider mrtc)




Gyniulus bufonilus (Chamberli.n)., (iam)




Altica sp., (1)
(a lea beetle)

amid bermuda grass

between rows of alfalfa

between rows of alfalfa

bermuda grass

amid sandspurs

8pu ul crimson clover

ul bermuda grass

evening primrose


bu 2pu

Col1embola, undet.


Orchesella ainsliei Folson


Bourletiella arvalis Fitch

B. savona Maynard

Sminthurinus ni',er (Lubbock)

Diptera, undet. (a)

Cecidovyidae, undet. (1)


Culicoids miss ssi ppiensis Hoffm. (a)

Cyclorrhapha, undet. (1)


Camptoprosopella sp., (a)



Orj.: ',--, -.- Ilay), (n & a)
( ...... .^.- bug)

0. irnsidiosus (a)

0. insidiosus (n)


Geocoris prob. punctipes, (e)
(a si- eyed bug)

p.Cr 1-r. bilobatus (Say), (n)

P. bilobatus (a)

amid sandspurs

amid burmuda grass

sandy beach, amid scattered herbs

ul amid low weeds

on sand, amid low weeds

near beach, amid sandspurs

in vegetable garden

ul bermuda grass in soybean field

3pu crimson clover

ul pusley

pu soybeans

pu pusley, in soybean field

sea rocket

pu purslane

TABLE 2--Contlnued


o & S

Taxon & Stage* of Prey d1 'l .i Site


Halticus bractatus (Say, (a)
(garden fiReahopper)


Nezara vlridula L., (2nd n)
(southern green stink bug}



__ .. pi sum (Harris), (n)

Anhi_ sp.

A. prob. gossypgi Glover
(cotton aphid)

Cicadollidae, under., {e, lst n)

Delphacdaec, undet. (e, 1st & 2nd n)

Sogatella kolophon meridiana (Beamer), (a)

Fulgoroidea prob. Flatidae, (1st n)


Spissistilu festimus (Say). (a)
(three-cornered alfaifa hopper)

2pu crimson clover, soybeans

ul soybeans


9pu ul crimson clover

ul evening primrose

Gnaphalium purpurnim L.

2ul egg in stem of undet. grass; soybean

4ul crab grass, egg in leaf

ul crab grass

ul soybeans

PU soybeans


Phylloxera sp., (a)


Phnacccuas solenoostis Tinsely, (a)
b~ciunOyiJ-ea i'jiuylq)

An-_-_- "li-kelj), (n B a)

A. rJmini3


Bracon dae

Aoanteles sp., (p)


NeCod-metia sangwani (Rao) (apterous a)


Conomyra insana (Buckley), (w)
(crazy anLT-

Crematogaster clara Mayr., (w)

Cardiocondvla nuda minutior Forel., (w)


Oluo-ista sp., (a)



Heliothis virescens (Fab.), (1)
(tobacco budworm)



Ha'lothrips gowdeyi (Franklin), (a)

ul amid bermuda grass in orange grove

bu on sand, amid scattered weeds

7bu 5ul bermuda grass! near roots and under
loot sheaths

ul crowfoot grass, (as above)

bu love grass, (as above)

ul soybeans

amid bermuda grass

amid bermuda grass

pu evening primrose

amid bermuda grass

near beach, amid sandspurs

pu soybean

ul pucley

TADLE 2--Continued


Taeon A Stage* of Prey l1 ul t11 Site

graminis Hood, (a) ul soybeans

Leptfthripa nr. macroocellatue Watson (a) pu soybeans
Phrasterothrips sp., (a) bu amid bermuda grass

Frankliniella binpionsa, (a) pu crimson clover
Ta flower thrip.)
F. bispinosa, (n) ul alfalfa
bisinosa, (a) 3pu ul soybeans

Caliothrios fasciatus (Pergande) ul alyce clover
(bean ttirip.)

*:-adult, e=eogg, Imm-imature, 1-larva, n-nymph, w-worker, let n (etc.)-lst instar nymph.
tbu-Geocoris bullatus, pu-=G. punctipes, ulG. uSjLLnosus; numbers-numbers of observations.
tcaI'll? i -'--rJ-.- P-Iman (sea rocket)-Brassicaceae; Alysicarpus vaginalis (L.) DC. (alyce clover), Gly-
rine-- i. r.;ri-L (soybean), Mtlcago eativa L. TalTa-lia) and Trifolium incarnatum L. (crimson
ci.ver)iFabaceae; Oenothera lacinflta Hill (evening primrose)-Onagraceae; Ce nchrus incertus Curtis
(sandspurs), Cynodon dactylon (L.) Persoon (bermuoa grass), Dactylocteniu, aegyp~ium (L.) Beauv. (crow-
foot grass), Diitaria adscendens (Hbtk.) iHenr. (crab grass), and Eragrostis refracts (Muhl.) Scribn.
(love grass)=Poaceie (all--il- Portoulaca oleracea L. (co-non purslane)-Portulacaceae; and Bichardia
scabra L. (pusley)=Rubiaceae. Simple-- listing of plant implies attack took place on plant; oherise,
soi-surface was substrate.
Data furnished by L. L. buschman.




0. 3 &i 0
i 0 0l
03 a; r.1
.T" [- J3 0 1

Taxc n and Stage*
of Unsuccessfully Attacked Arthropod 4 0 01 I1 HabHtat Apparent Reason for Failure



Tcnn3eseGellu formicu. (Emerton) (ads) 2.0



Ceutorhynchus sp. (a) 3.4

ul on soil


6.3 pu

>1 bu

Hypea postca (Gyllenhal) (1)

CoLlemnola, undet.

outran Geocoris

evening primrose while weevil was nested in terminal
leaves, it detected furtive feeding by
Geocoris, then dislodged and outran

crimson clover drove Geocoris away by swinging anterior
end toward bug

on sandy soil while running from closely pursuing
Geocoris, collembola escaped by spring-
ing iOto and hiding amid nearby clump
of dead leaves; Gencoris searched on
soil, but failed to Tind where prey had



OriG-e -1.i _- ._ ay), (a)
(,.,, .i ., - bug)

0. insidoosus (a)


pachybrnachiuas sp., (n)
,a paceWan)



A, 1 i, wr. pisum (Harris)

(pea aphid)


Clastotr anthocephala Germar (a)
usflower spittlebug)


Enpoasca sp., (n)

Hymenoptera, undet., (winged a)

formicidae, undet., (w)

Brachymyrmex sp., (w)

Car docndyla nuda minutior Porel,




crimson clover failed to penetrate running Orius;
Geocoris did not pursue

ul bermuda grass jumped to safety

ul crabgrass

ran from approaching Geocoris

3.5 2pu crimson clover while continuing to feed, on 2 occasions
I aphid "waggled" abdomen repeatedly
until 2 separate Geocoris quit attempt-
ing to insert beak & wa-ked away; many
others simply dropped from plant when a
Geocoris approached

3.2 ul evening primrose detected furtive feeding by Geocoris,
jumped from plant

2.5 pu crimson clover failing to outrun Geocoris, it jumped to
adjacent leaf; Gojco'r-s couldn't quite
reach across gap with legs and would not
fly to reach nearby prey

Ca 2 bu sandspur having impaled prey on leaf parallel to
its own, Geocoris lifted prey into air,
causing iti own leaf to buckle, thus
throwing botn insects to ground

3.2 pu pusley repeatedly failed to penetrate passive

1.3 ul on sandy soil Geocoris failed to penetrate, ant then

1.3- 3bu 3ul on sandy soil single attack failed to secure prey on
1.7 beak; 3 ants appeared injured

Taxon and Stage-
of Unsuccessfully Attached Arthropod

Conomyrna flavopecta M.R. Smith, (w)


Oecophorndae, undet., (1)



Caliothrins fasciatus (Pergande),

2.1 ul

4.6 ul goosegrass

1.1 ul alyce clover

TABLE 3--Continued


Sn' d H0 btat
.hi d) 3 l ID Ilbia

*a-adult, n-nymph, 1-larva, w-worker.
tbu-Geocoris bullatus, pu=g. punetipes, ul=G. uliginosus; numbersanunmbers of observations.
t'L.- ir-r gi"alis (L.) DC. (alyce clover), and Trifolium incarnatum I.. (crimson Clover)=Fahaceae; Oenothera laciniata
i .1'. primrose) =Onagraceae; Conchrus incertus Cursti (sandspurs), Cynodon dactvlon (L.) Persoon (bermuda grass).
Diitcaria ad, endens (ibtk.) Henr. (crab grass), and Eleusine indica (L.) Te goosegrass)ePoaceae (all wild); and
Ritardun scabra L. (pusley)-Rubiaceae.

Apparent Reason for Failure

injured or dying ant under grass blades
lying on ground thrashed about when
Geocoris repeatedly attempted to impale it
by inserting its beak between leaves;
Geocoris finally left

having inserted its beak into the prey's
thorax, the Geocoris began to tug back-
wards to break prey's foothold on the leaf
both were on; suddenly, when its beak
apparently dislodged from the prey, the
Geocoris tumbled backwards and ran away
from the still motionless prey

dropped fr-m leaf when touched by tip of
beak; nearby chrips was subsequently taken

are no field records for genera of the subfamily Geocorine

other than Geocoris, although I have raised Hypogeocoris

piceus (Say) in the laboratory for more than 1 generation

with no apparent problems, using the same diet that I use

for Geocoris spp. (i.e., eggs and small larvae of the

soybean looper, Pseudoplusia includes Walker, along with

fresh green beans) (Crocker, unpublished data). These ob-

servations indicate that H. piceus may have feeding habits

similar to those of Geocoris spp. Because most other

lygaeids are phytophageous, however, it is possible that

phytophagy may be more important in some other geocorines

than it is in Geocoris.

On 2 occasions, I have been bitten by specimens

of G. uliginosus: once by an adult female, which crawled

between my fingers and began feeding through the tender skin

there, and once by a 4th instar nymph, which crawled un-

noticed from the soil onto the back of a finger where it

began to feed. In both cases, the bite created a noticeable

burning sensation (much like an ant sting) which was

localized at the bite. In both cases, the burning sensation

subsided after several minutes. No systemic effects (such

as nausea) were noted. The burning sensation was probably

due to saliva being pumped into the wound through a

specialized canal formed between the stylets of most Hemip-

tera (food being characteristically taken up via a second,

similar canal). Such behavior has been reported previously

in the New World only by Knowlton (1940), who experienced

similar effects when bitten by G. decoratus. Feeding by

Geocoris does not alert its prey, however, for I have ob-

served that Geocoris are often able to feed on other

arthropods (much larger than themselves) without being


Prey size. Most prey taken were smaller than the

Geocoris, and many prey of adults were less than 0.5 mm

in length (Table 4). I was unable to recover many of the

smallest prey for taxonomic identification, and their

lengths had to be estimated. Some of the prey successfully

taken by the Geocoris were, however, so much larger than

the predator that--except where a vital organ might be

destroyed--such feeding would be expected only to debili-

tate the prey or to allow an opening for the entry of

pathogens. An extreme example of such sub-lethal feeding

occurred spontaneously in the laboratory when a tiny, 1st

instar Geocoris nymph climbed onto the back of a full-grown

soybean looper larva several hundreds of times its own

mass, and fed on the larva without being detected.

It is reasonable that among predators which are

otherwise essentially alike, larger predators would con-

sume prey which, on the average, were larger than the prey



A. Lengths of Arthropods Successfully Attacked by
Adult Geocoris spp.

Prey Length (mm)
Mobility Mean SD SE_ Range n

Sessile 1.60 0.88 0.23 0.57-3.3 14

Ambulatory 1.26 0.86 0.12 0.25-3.5 (8.7) 56

Saltatory 0.76 0.51 0.21 0.50-1.8 6

Flighted 1.88 0.86 0.20 0.66-4.9 18

B. Lengths of Motile Arthropods Attacked by Geocoris Spp.*

Fate of Length (mm)
Prey Mean SD SE- Range n

Captured 1.38 1.13 0.12 0.25-8.7 97

Escaped 2.18 1.31 0.28 0.50-6.3 22

*Means significantly different (p=0.0044).

of smaller predators. I have been able to demonstrate a

length-to-length relationship between Geocoris and their

prey, however, only in the case of prey which are winged

(Fig. 1). For prey which are sessile, ambulatory, or

saltatory (each prey being listed in only 1 group), the

computer-generated, linear regression line was not signifi-

cant at p=0.05 (Figs. 2, 3, 4). I feel this failure was

due to the variability of the data in relation to the

sample size, a condition aggravated by my lack of data

for small nymphs of Geocoris.

Prey defenses. In general, Geocoris attacked prey

which were capable of only limited or passive defense.

Of 125 prey they attacked, 109 posed no probable hazard

to the Geoccris, and only 2 may have had the capacity to

injure the Geocoris seriously. No Geocoris was actually

harmed by a prey during the course of my natural observa-

tions, and no significant differences were found among the

3 species of Geocoris with respect to the potential

dangerousness (measured on an artificial scale) of their


Geocoris often are able to take a prey without

triggering a defensive reaction. In 125 attacks by Geocoris

I observed in nature, the success rate was significantly

(p=0.004) greater in those attacks where the prey made no

effort to escape prior to being contacted (Table 5A). Even


4 +



I *


0 '
t------------------------ -- ------, --------
3.0 3.5 4.0 1.5
Predator Length (inn)
Figure 1. Lengths of flighted prey of Geocoris spp. plotted against the
lengths of Cocccris. Regression line (y= 0.83x. 1.24) is significant
at p= 0.0288; R2= 0.24. Legend: A= 1 and D= 2 observations; *= predic-
ted values.

3.5 +



2.0 A A


1.5 +



0.5 *
I ------------------------------------ ---- -+-------------.--------
1.5 2.0 2.5 3.0 3.5 4.
Predator length (nm)
Figure 2. Lengths of sessile prey of Geocoris spp. plotted against the
lengths of the Geocoris. Pegression on data not significant at p= 0.05.
Legend: A= 1, B= 2, and C= 3 observations.


4.o +

3.5 + A

3.0 A

2.5 i+ A


1.5 + A

1.0 A B B
A c
0.5 +* A A 8 A 8 A C 8 A A

0.0 +
|-- --. --+- --- -.. -.-. --- -..- --.. - 5- -. ------.--

Legend: A-l, B= 2, and C 3 observations.

2.0 +

.8+ A



S1.2 +

1.0 +

0.8 +


0.6 A

0. A
1.5 1.0 2.5 3.0 3.5
Predator Length (mn)

Figure 4. Lengths of saltatory prey of Geocoris spp. plotted against the
lengths of the Geoooris. Regression on data not significant at p- 0.05.
Legend: A= 1 and B= 2 observations.



A. (X2=8.284 with 1 d.f.; p=0.0004)

Observed Frequency
Expected Frequency
Cell X2
Percentage of Data
Row Percentage Prey Prey
Column Percentage Captured Escaped Total

54.00 14.00 68.00
No observed 49.40 18.60
defensive 0.40 1.10
behavior 64.29 16.67 80.95
79.41 20.59
88.50 60.87

7.00 9.00 16.00
11.60 4.40
Defensive 1.80 4.90
behavior 8.33 10.71 19.05
observed 43.75 56.25
11.48 39.13





TABLE 5--Continued

B. (X2=15.656 with 1 d.f.; p=0.0001)

Observed Frequency
Expected Frequency
Cell X2
Percentage of Data
Row Percentage
Column Percentage




10.00 10.00 20.00
No observed 16.10 3.90
defensive 2.30 9.50
behavior 12.20 12.20 24.39
50.00 50.00
15.15 62.50

56.00 6.00 62.00
49.90 12.10
Defensive 0.70 3.10
behavior 68.29 7.32 75.61
observed 90.32 9.68
84.85 37.50

66.00 16.00 82.00
Total 80.49 19.51 100.00

those target prey that resisted subsequent to being con-

tacted or stabbed by the Geocoris had significantly

(p=0.0001) better chances of surviving than did those whose

only response was to thrash about with their feet subsequent

to being lifted into the air (Table 5B). Although many

prey did not react at all as far as I could tell, there

was no evidence that they were paralyzed, because many prey

continued to move for several sec and several prey that

were taken from the Geocoris continued to walk about within

the collecting vial until they were killed with isopropanol.

Running was a common defense, but Geocoris were

able to overtake 6 of 9 such target prey, including such

rapid prey as Orius. The only spider that I saw attacked

was able to escape by running on the soil (Table 3). Per-

haps the most effective defense commonly observed was for

the target prey simply to drop from the plant; such target

prey often escaped. One aphid, Acyrothosiphon pisu;

(Harris), on crimson clover drove away 2 successive adults

of G. punctipes "waggling" its rear end while continuing

to feed. One collembola which had been unable to break

the pursuit of a G. bullatus by running across the soil,

escaped by springing a few cm into a pile of debris; al-

though the Geocoris searched the area and for several sec

appeared tc be watching for movements of its lost target,

the collembola remained motionless until the Geocoris

wandered away and thus was saved. Although, as in the case

of the Orius previously referred to which was caught after

being chased several times around a floral head, Geocoris

were sometimes quite persistent, they would often abandon

a prey if it resisted capture. This tendency to concen-

trate on easy prey may be due to the fact that the Geocoris

I observed were in the midst of rather abundant prey. In

such a situation, it may take them less time and energy

to obtain a given amount of food if they concentrate on

easy targets. Those Geocoris which were more persistent

may have been "hungrier," and thus under more pressure to

make sure that they fed on whatever was available.

A second reason for Geocoris to avoid struggles

with its prey is that since the beak is the only organ

they use (at least this is true for the present 3 species),

Geocoris are not suited to struggle effectively against an

active or dangerous prey. A Geocoris can only attack prey

that are far enough away that it can extend its beak to

penetrate the integument.

Developmental stages of prey. Although laboratory life-

table data lead Dunbar and Bacon (1972) to suspect that G. puncti-

pes might feed primarily on eggs in nature, my field data (Table

6) indicated that adults, nymphs, and larvae constituted almost

97 percent of the target prey of Geocoris, with eggs and

pupae making up the other 3 percent. Under differing



Structure Stage and Sex
Foodplants Fed on of Geocoris


1. Gnaphalium pupiu L. leaf blade adult
(rabbit tobacco)


2. Oenothera laciniata Hill leaf blade adult
(evening primrose)


3. C nodon dactylon (L.) Persoon stem 4th instar
(be.rmuda grass)

4. Digitaria adscendens (Hbtk.) Henr. leaf sheath adult

5. Panicum lancearium Trinius ripe seed adult
on soil

6. Richardia scabra L. flower adult

circumstances, these percentages may vary considerably.

Geocoris must rely on their antennae to find insect eggs,

but they are able to find motile prey using either their

antennae (in the dark) or their eyes (in light) (Section

II). The zone of discovery of motile prey is probably

greater than for immotile prey, thus making the discovery

of motile prey more likely, if both kinds of prey are

equally abundant.

In nature, Geocoris hunt singly and primarily are

active searchers (members of en copula pairs take prey, but

do not share it). Exploring their habitat mainly on foot,

Geocoris respond to moving prey at a distance and investi-

gate crevices for hidden prey. They also seem able to find

eggs inserted into plant tissue. Although Geocoris are

able flyers and often fly between plants, they apparently

will not fly to reach a given prey across even a small air-

space. If a Geocoris cannot reach the nearby plant part

the prey is on either by a simple indirect route or by

reaching across with its front legs and securing a foothold,

it will abandon the target prey. This is possibly a

question of energetic and natural selection: the shock

waves caused by the landing of a Geocoris may alarm the

target prey sufficiently often to make a flighted approach

a poor investment of time and energy. If that is so,

natural selection will have favored those individuals that

would not fly to reach a target prey. Rarely, a Geocoris

will take flight with a prey on its beak. At times,

Geocoris wait quietly for many minutes, and attack prey

that come near.

On most occasions, Geocoris attack a prey simply

by walking or running up to it, extending their beak, and

quickly inserting their stylets; following this action,

they may lift the prey into the air, holding it directly

in front of them,which deprives the prey of use of its

legs for escape. Often, they will palpate the target

prey with their antennae prior to impaling it. Palpation

continues intermittently throughout feeding. When the

target prey is rather large, the Geocoris often will

approach it slowly and cautiously; Geocoris commonly can

feed from such large prey without apparently being de-

tected, although the prey remains normally responsive.

Prey preference. The importance of differing types of

prey varied considerably from site to site. For that reason, and

because all 3 species did not tend to be abundant in any

given habitat, it is difficult to give a precise assess-

ment of any preference Geocoris might have for particular

types of prey. Aphids, mites, and thrips were commonly

taken, and probably are commonly important in their diets.

Although ambulatory arthropods made up the majority of

target prey (86 ambulatory prey, vs. 25 flighted, 18

sessile, and 11 saltatory prey), prey with other types of

motility were of considerable importance at particular

sites. Members of some higher taxa generally thought to

be heavily fed on by Geocoris are poorly represented in

my data (Table 2), this condition possibly being due to

the scarcity of such prey types (e.g., Lepidoptera larvae)

at sites I sampled.

Habitat and microhabitat preferences. Insofar

as I can tell, all Geocoris spp. (and perhaps all

geocorines) occur in various mesic-xeric, herbaceous

habitats. Because Geocoris indulge in a limited

amount of harmless phytophagy (Crocker, unpublished data),

it is possible that the availability of food plants may

influence their habitat choice. Physical characteristics

of the habitat may also be important. Some of the apparent

differences in prey preferences among Geocoris spp. (Tables

1, 2) may be actually due to differences in preferred habi-

tats. In Florida, I found that G. punctipes and G. uligi-

nosus were commonly abundant in crops, with G. punctipes

tending to be more evident high on the plant and G. uligi-

nosus being more heavily concentrated at ground level.

Their vertical distributions overlapped completely, but G.

uliginosus tended to be underrepresented in sweep and

vacuum samples. G. bullatus, and to a lesser extent G.

uliginosus, were abundant in sandy, somewhat xeric habitats

among sparse weeds and grasses and near beaches. G. uligi-

nosus appeared to be more common than the other 2 under

the shade of live oaks, and could at times be found in

numbers amid the oak leaf litter. Occasionally, in rather

fine-grain, weedy habitats, all 3 species occurred in roughly

equal numbers, but usually G. bullatus was not abundant

when associated with G. punctipes. It is puzzling that

G. bullatus and G. uliginosus (similar sizes) occur together,

whereas G. bullatus and G. punctipes (different sizes)

usually do not. It is possible that G. bullatus and G. uli-

ginosus exist together without partitioning some habitats,

because both have refuges (other habitats) wherein they are

not in competition. Additionally, G. uliginosus may be

somewhat more prone to necrophagy than are G. bullatus or

G. punctipes. Differences in predator sizes and vertical

distribution patterns could easily explain the ability of

G. punctipes and G. uliginosus to minimize competition in

a given macrohabitat.

Geocoris are highly polyphagous. In a family

(Lygaeidae) many of whose members are important pests (e.g,,

chinch bugs, Blissus spp.), my data indicate that only a

minor portion of Geocoris' diet comes from plants. An

even smaller portion of their diet is derived from feeding

on whole and fragmented insect corpses (Crocker, unpublished

data). The majority of their diet, however, comes from

predation upon motile and immotile forms of a wide range

of terrestrial arthropods.

Concerning the effects of Geocoris upon the popu-

lation dynamics of other arthropods, I have noted that

where aphids, thrips, or spider mites occurred in numbers

along with Geocoris, these items were prominent in

their diet. The same is true of PRhodesgrass scale and of

other types of prey. This indicates that Geocoris inflict

mortality on prey species in proportion to the relative

abundance of that prey and that they probably respond to

changes in the density of a prey in direct proportion to

the sign and magnitude of that change (a directly density-

dependent functional response). Tamaki (1972) clearly

demonstrated a direct numerical response by Geocoris to

increased availability of aphids under peach trees in

Washington. It thus appears that Geocoris inflict mortal-

ity on a prey species in direct proportion to its abundance,

thus tending to stabilize the levels of those prey at

lower levels than they might otherwise attain. Because

Geocoris are highly polyphagous, they would be expected

to respond functionally rather than numerically in most

cases to changes in the relative or absolute density of

a given prey species. A noticeable numerical response

would generally be expected only if food were a limiting

factor for the Geocoris at that site and only if the target

prey made up a considerable fraction of the total, avail-

able food. An exception to the preceding would be where

the Geocoris exhibited a marked preference for the target

prey over other available prey, no such exceptions are

presently known.

Importance of Geocoris spp. Many of the prey of

Geocoris are of considerable economic importance; many are

resurgence pests which are problems only when a natural

factor (e.g., weather) or a manipulated factor (e.g.,

pesticides or cultural practices) temporarily releases

them from control by their natural enemies. The fact that

so many of our pests are of this type speaks strongly for

the pervasive pressures exerted by entomophages such as

Geocoris. Because Geocoris are primarily predators, and

because they are often among the most abundant insect

species in a crop, it is obvious that they must exert

tremendous pressures upon other species in the crop--

pressures which tend to reduce the pest load on the crop

and which reduce the need for applications of chemical


Menke and Green (1976) failed to detect a numeri-

cal response by Geocoris spp. to the velvetbean caterpillar,

Anticarsia gemmatalis HUbner, in soybeans during a less than

2 month period in Florida, and interpreted this as meaning

that Geocoris were not a significant source of control for

that pest. As previously stated, the breadth of the food

base of Geocoris makes it unlikely for numerical response

to have occurred even if Geocoris were inflicting consider-

able mortality on A. gemmatalis (a condition which may or

may not exist). Another factor which tends to complicate

the issue are that 2 months may not be sufficient time to

allow for population increase due to reproduction (Crocker

et al. 1975). Even so, had we found Geocoris to have

markedly oligophagous habits, we would be more favorably

inclined toward the conclusions of Menke and Green.

A similar case can be found in Gonzalez et al.

(1977), in which Geocoris were found to correlate with

flowers of the cotton plant, but not with any of several

important pests. Special considerations in this case are

that several small arthropods (thrips, mites, whiteflies,

and aphids) were not sampled due to mechanical considera-

tions. In the light of our observations of the response

of Geocoris spp. to flower thrips in soybeans, I would

tend to doubt those authors' hypothesis that the positive

correlation of Geocoris with cotton flowers indicated

the importance of those flowers as food; I would instead

point to the relationship of thrips to flowers, and suggest

that it was to these pest insects--not the flowers--that

the Geocoris were responding. I might also note that

mites and aphids are commonly taken by Geocoris, a fact

which may account in part for why those organisms are not

considered primary pests of cotton. Again, the broad food

base of Geocoris makes it unlikely that a numerical

response to the target prey would have been detected, even

if they were regulated to some extent by Geocoris. As

workers such as Gonzalez et al. continue to refine the

techniques of population estimation in crops, hopefully

we will all be in better positions to evaluate our crop

systems and,subsequently, to manipulate those systems so as

to minimize the need for the use of chemical pesticides.


Phytophagy (Tables 6, 7, 8) was observed during

every month from April through November, and is probably

a year-round activity in Florida. Typically, feeding

times were fairly short (<1 min), but would occasionally

last for several minutes. Quite commonly, a given Geocoris

would feed repeatedly from plants over the course of an

hour or so.

At times, the Geocoris displayed a strong tendency

to feed on plants, even in the presence of potential prey

or danger. In 1 case (Table 7, #1), a G. punctipes adult

fed for 8, 8, 5 and 22 min with pauses of only a few sec

between feedings. During that prolonged period, an

encyrtid wasp and an imported fire ant Solenopsis invicta


Structure Stage and Sex
Foodplants Fed on of Geocoris

1. Brassica pekinensis Ruprecht leaf petiole adult
(Chinese cabbage)


2. Glycene max (L.) Merrill leaf adult dP

3. Trifolium incarnatum L. leaf blade adult d'
(crimson clover)


4. Oenothera laciniata Hill leaf blade adult d'
(evening primrose)

5. Digitaria adscendens (Hbtk.) Henr. seedhead 3rd instar


6. Portulaca oleraceae L. leaf adult
(common purslane)


7. Richardia scabra L. flower adult
(p usley)



Foodplants Fed on


1. nthalium pur .prlinn L.
(rabbit tobacco


2. Cassia obtusifolia L.

3. GLycine max (L.) Merrill

4. Trifoli-m incarnatum L.
(crimson clover)


5. Cynodon dactylon (L.) Persoon
(bermuda grass)

6. Dactyloctcenium aefyetium (L.) Beauvoli
(crowfoot grass)

7. Dxgitaria adscendens (Hbtk.) Henr.
(crabgras s)
S. Eleussne indica (L.) Gaertnear


9. Fragaria ananas sa Duchesne
(cultivated strawberry)


10. Richardia scabra L.

floral head

foliar nectary


leaf blade

leaf blade

leaf sheath


leaf blade

leaf blade

dead leaf

leaf blade

ripe fruit (seed
or flesh)

leaf blade


Stage and Sex
of Geocoris




several adults

4th instar
5th instar

5th instar




4th instar


4th instar

several adults

several adults

Buren, approached the Geocoris on separate occasions; each

walked about it, and even tapped the bug with its antennae.

The Geocoris showed no response to either of the intruders,

although they usually would have served as strong releasers

of attack or retreat behavior for Geocoris. After it

finished feeding, the Geocoris seemed to be normally alert

and active. On another occasion (Table 8, #2), a G. uligi-

nosus adult o was discovered feeding from an erect nectary

that occurs between the basal leaflets of Cassia obtusifolia.

After a few minutes, an ant (Conomyrma nr. flavopecta)

approached the nectary and attempted to feed. The Geocoris

turned toward the ant, extended its beak forward, drove the

ant away by running at the ant with its beak, and resumed

feeding from the nectary. This behavior on the part of the

Geocoris was unusual; on most occasions a Geocoris will run

from an approaching Conomyrma.

Geocoris feed on plants throughout at least most

of the range of temperature and humidity conditions that

they normally encounter in Florida (Fig. 5). I have seen

them plant feeding above hot, dry soil under bright sunlight,

above earth damp from recent rains, and even during light

rain. Moreover, in all cases where I observed phytophagy,

potential prey (of types known to be taken by Geocoris)

were quite abundant. Although present evidence indicates

that no particular set of weather conditions is necessary

to trigger phytophagy, it seems probable that weather af-

fects the amount of such feeding that occurs.

Discussion. Under natural conditions, G. bullatus,

G. punctipes, and G. uliginosus feed not only on live prey

and dead animal matter (Crocker, unpublished data), but also

on a wide range of herbaceous flowering plants, both mono-

cots and dicots. Several available herbs, however, such as

Euphorbia supina Rafinesque (Euphoribiaeceae) and Polypremum

procumbens L. (Loganiaceae), were not fed on in my presence.

The present lists (Tables 6, 7, 8) of natural food-

plants are probably far from complete, thus it would be

premature to make any firm statements concerning interspe-

cific differences in the phytophagous habits of Geocoris.

Even at this point, however, it is clear that there is

considerable overlapping of foodplants among the species

of Geocoris. Because of the diversity of the foodplants of

Geocoris, it seems probable that certain physical or chemi-

cal characteristics of the plant or of the habitat are more

important than the taxon of a plant in determining whether

or not any species of Geocoris feed upon it.

Although the availability of suitable prey is

certainly of great importance in determining the local

abundance of Geocoris, there are many plants and many

habitats that are not frequented by Geocoris in spite of

the abundance of aphids and other known prey types. Because

Geocoris are partially phytophagous, it is probable that

the availability of suitable foodplants is an important

element in their choice of habitat. Tamaki (1972) noted

that although Geocoris spp. were quite abundant on the

floor of the orchard, they were absent from the peach trees

themselves. Aphids on the trees were quite safe from the

Geocoris, but thousands of those aphids that fell to the

ground were consumed by Geocoris before they could return

to the trees.

Sweet (1960) discovered that geocorines could

survive for prolonged periods on sunflower seeds and water

in the laboratory, and proposed that seedfeeding was prob-

ably of great ecological and evolutionary significance

in the Geocorinae, accounting in large part for their

great abundance. Whereas I agree that phytophagy is

certainly of great ecological and evolutionary importance

in the Geocorinae, present evidence indicates that the

emphasis purely on seedfeeding should be broadened, because

only 1 of 31 (=3 percent) of my plantfeeding records

definitely involved seedfeeding, whereas 21 (=68 percent)

definitely involved vegetative structures.

There is still much to be learned concerning the

precise function or importance of phytophagy by Geocoris,

although the wide range of temperatures and saturation

deficits (Fig. 5) under which I observed plant feeding

Figure 5. Atmospheric saturation deficits at which phytophagy by

Geocoris spp. occurred at various temperatures in Florida. Regres-

sion on data not significant at p=0.05. Legend: A=1 and B=2

observations; *=predicted value.


30 +

25 +

.i A
20 0
iri B

15 A


10 + A


5 +
I --- --------- --------- -+- ----- ---- -----+-------- ----- -

20 22 24 26 28 30 32 34
J'eknperature (C)

strongly indicates that plant feeding is a normal activity,

not merely a reaction to unusually stressful conditions.

The difficulties encountered by several recent workers

attempting to correlate the population dynamics of some

species of Geocoris with those of certain pest species may

be due in part to the buffering effect of phytophagy. It

should be noted, however, that during the time in which we

accumulated the 31 records of phytophagy reported here, I

also recorded 18 instances of necrophagy, 26 instances of

attempted predation by the Geocoris, and more than 125 in-

stances of successful predation upon other arthropods.

The primary role of Geocoris is that of predator.

That a weed--or the crop plant itself--may be an

important source of supplemental moisture or nourishment

for valuable predators such as Geocoris has significant

implications for pest management. Predator-plant

interactions are of particular import in view of recent

discoveries by Altieri et al. (1977) concerning the poten-

tial usefulness of weeds in cropping systems. Toleration

or even the encouragement of non-noxious weeds (i.e., those

which do not harbor important pests of the crop), in

fencerows, etc., may encourage such predators by providing

a source both of alternate prey and of foodplants. The

planting of crops known to be foodplants near other crops

needing protection by predators may in some cases accomplish

the same end.


Roughly similar amounts of time were spent in

collecting feeding records for all 3 species (Tables 9,

10, 11); the fact that I have several times as many records

of necrophagy for G. uliginosus as I do for the other 2

species indicates that feeding on dead animal matter may

be more common in G. uliginosus than in G. bullatus and G.

punctipes. If this is true, it might help explain why

G. uliginosus are often abundant in Florida habitats where

either G. bullatus or G. punctipes are also numerous.

Seldom are both G. bullatus and G. punctipes abundant at

a single site in Florida; this may be due to competitive

exclusion, with the former species more successful in sparse-

ly, sandy habitats and the latter species better adapted

to field crops and other lush, herbaceous habitats.

A single record for G. uliginosus is my only

observation of coprophagy (Table 11, #12); such feeding is

probably of little consequence. During periods of prey

scarcity such as might occur in soybeans following the

devastation of populations of lepidopterous larvae by the

fungus Nomuraea rileyi (Farlow) Samson (Allen et al. 1971),

necrophagy might, however, temporarily become very important,

lessening precipitous mortality and emigration of the

Geocoris. Conversely, it is possible that corpses of

arthropods killed by some pesticides may present a linger-

ing threat to surviving or immigrating Geocoris.



and Stage
Material Fed on Site of Feeding of Geocoris

1. Aphid (mere husk), covered on soil adult '

with an imperfect fungus,

Cladosporium cladosporio-

ides (Fres.) de Vries

2. Fly larva (Diptera: on underside of a leaf of adult

Syrphidae), withered Gnaphalium purpurium Hill



and Stage
Material Fed on Site of Feeding of Geocoris

1. Southern green stink bug, Nezara viridula soybean plant adult '

L. (Hemiptera: Pentatomidae), adult,

15.1 mm long,* partially decomposed

2. Pea aphid, Acyrothosiphon pisum (Harris) aphid wedged into axil of adult

(Homoptera: Aphididae), withered leaf of crimson clover

3. Fly (Diptera: Tephritidae?), shriveled on leaf of soybean plant adult

*Data collected by L. L. Buschman.


Kj L~lja red on

1. otrtArpoJ, 0.1 -n long

2. Mdndlbli & *i0.. la. drLed fraoen- of

Is-A, pAibly Phyl ophf- op. (Coleoptsr;

Scr0b0e.4ol, p1i-0 ... 3.S long

3. "tl sLd4B (Dlptera Ccidoeyildesl

4. Gaole of *nt tyenaoptera: Pfor Jcide,.

1.17 lo.q

S. Viogid, -1. fti. -'t. Solano pa.

9B00a0- (Fo&r.)

J. lootottot Ml.- of ftr, aCt. 0. invicta

7. ,hYba .. h-, vb.njta (Say) (Hol.iptoeA

LygdLidae). adolt, bAdly ch.w.d on by 0n ant, invictA 000.-

I. G00d4 fleahoppw-, ilalticus bcac aui

2. Oouoio. of lafhaoppr (HooaopyerA:


10. Syafh )Oolcpfser. tklplec,4Ae)

11. Sysph lonopcerji OeLphcidad)

12. r-.eB of pltot feeder (Lepidapttc.a?)

cnd 3c0q.
of 00000-0
Soi ce0.o1.0
5thi lnlcar


410 in.1.0

sit. of r.dlnq

c00-p.. In fold ....ed by

0rlss blde closing along

Its id-rLb
l e uldoli

Olid moybe00 flo-ero

on i.l, -id b.asods tra.i

oa 0o11

co =11, -oid bmmbuda qga

-t so0l1, 0d a.. c. g00.se1

A. .Ilt of pimso.n c1.1o

on soybea leaf

-oof OIf *lIO c10v0

1.00 f qoo.11

I1.f of 9000071E000

Adult j

4th Il~u

3t~h L..-,r

.dolt 2




The means by which a predator detects potential

prey affects the kinds of prey taken and the conditions

under which those prey are vulnerable. Geocoris spp.

attack many kinds of arthropods (Section I), and are widely

thought to be of great importance in the natural regula-

tion of many agricultural pests. Although the roles of

the various sensory modalities in prey-capture by Geocoris

have not been investigated previously, field observations

have led me to suspect that Geocoris (appropriately called

"big-eyed bugs"), rely heavily on visual cues for the

location and capture of motile prey. Movements by a human

observer located 0.5 m or more from a Geocoris in the field

often stimulate the bug to pivot toward the researcher.

Geocoris characteristically orient toward moving arthro-

pods that are within several cm of them, and quickly

implement either attack or avoidance behavior. Geocoris

bullatus, for example, commonly attack and kill worker

ants of Cardiocondyla nuda minutior Forel, but usually run

from the somewhat larger ants, Conomyrma insana (Buckley)

and Solenopsis invicta Buren (Crocker, unpublished data).

The natural diet of Geocoris also includes many cryptic

or immotile items, such as insect pupae and eggs, dead

arthropod matter, adults of the Rhodesgrass scale (Tables

1, 2) and many herbaceous plants (Tables 6, 7, 8).

The eyes of Geocoris are probably poorly suited

for distinguishing between food and inedible materials.

By contrast, the antennae are ideally suited for such a

task and Geocoris employ them extensively when exploring

their surroundings or preparing to feed on immotile objects,

such as insect eggs (Crocker, unpublished data). Geocoris

even palpate their prey while feeding. However, the 3

species of Geocoris found in Florida rarely touch the food

with their legs and the beak generally remains retracted,

except when it is being groomed and immediately prior

to feeding. Thus, I hypothesized that adult, male

Geocoris punctipes (Say) rely heavily on their eyes in

order to find motile prey, and use their antennae for

locating immotile prey. The experiment reported herein

was conducted to test these hypotheses.

Materials and Methods

Sixty adult males of G. punctipes, from an alfalfa

field at Gainesville, Florida, were randomly divided into

2 groups of 30. Each individual of 1 group was exposed

to welding grade CO2 gas for about 2X the time required to

render it inactive. Iris scissors were used to sever

each of its 4-segmented antennae near the proximal end of

the 2nd segment (leaving slightly more than 1 segment in-

tact). The insect was then placed into an individual 9-cm-

diameter glass petri dish and allowed to recover from

the effects of the CO2. Individuals of the other group

were treated similarly, but their antennae were left in-


The experiment was a modified factorial design,

in which treatment variables were: (1) the presence or

absence of the antennae, (2) eggs or newly hatched larvae

of the cabbage looper, Trichoplusia ni (HUbner) for food,

and (3) 14hZ:10hD photoperiod vs. darkness interrupted

with light only during the 2-4 min. required for daily ob-

servations. Eggs were offered as food only under 14hL:10hD

photoperiod. Each predator was offered 30 fresh prey-items

daily (more than were ever consumed), and data were the

number of prey (x) consumed per day. Eggs were placed

on 1-cm pieces of typing paper, and the larvae on fresh

green beans. The eggs and larvae used for food were

laboratory produced according to the methods of Leppla and

Vail (1977). These prey were chosen because of their

similarity to each other in most respects other than motil-

ity, and because I knew these prey to be both attractive

and nutritious (Crocker, unpublished data).

The sample variance (s2) is directly proportional

to the sample mean (R), when the data are the number of prey

consumed daily by Geocoris under laboratory conditions

(Crocker, unpublished data). For this reason, and based

on previous findings concerning rates of prey consumption

by G. punctipes (Crocker et al. 1975), I used only adult,

male G. punctipes, ran the experiment at 251C, used 10

predators per treatment, and took 6 observations per preda-

tor, with the goal of being able to differentiate (p=0.05)

between means differing by 2.00.

Because I was dealing with count data with many

"zero" observations, the data were transformed according

to /x+1/2, in order to stabilize the variance; subsequently,

I performed a multiple factor analysis of variance. Sig-

nificant (p=0.0002) interaction between the factors made

it necessary to test the main effects by comparing the

levels of that single factor; this was done using student's

t-test, d.f.=234 (Table 12).

Results and Discussion

Altered individuals (those lacking all but slightly

more than 1 segment of their 4-segment antennae) consumed

significantly (p=0.05) fewer eggs than did intact predators

(Table 12). Only 4 out of 1,800 eggs offered these al-

tered predators were counted as having been destroyed, and

these eggs may actually have deflated due to injuries




14hLIlOhD Nearly ContI-nuouLA. DarkneaB'

Antennae lntect Antennae Altered Antennae Intact Antennae Altered

Larvae Eggs LarvBE Egg Larvae Eggs Larvae Egg.

Actual nuber. of prey conBsmed daily

S8.33 1.13 10.82 0.07 9.15 --- 5.93 ---

CL 95* (5.85, 8.38) (0.24. 1.14) (8.44. 11.40) (0.00., 0.40) (6.84, 9.80) -- (3.99. 6.36) ---

Data transformed according to /X+0.5

S2.75 1.07 3.22 0.74 2.96 --- 2.37 ---

C1951 !0.23 !0.21 10.23 10.21 !0.25 -- -0.25

*These 95% confidence limits are asynaetrlcally distributed around their respectlva means, because they were obtained by calculating the upper and
lower confidence limits of the transformed data and subasquently reversing the transformation process.

tso offered as food.

incurred during their handling. It may be said, therefore,

that altered G. punctipes were probably completely in-

capable of feeding on the eggs. This inability of altered

G. punctipes males to feed on eggs cannot be due to sur-

gical trauma, because such individuals, when fed larvae

under 14hL:10hD, consumed no fewer prey (p=0.01) than did

intact predators (the fact that the altered Geocoris

actually consumed more larvae than did their intact counter-

parts can be ignored for the purposes of this experiment).

Randomly distributed mortality (due to handling, etc.) among

the larvae probably inflated the apparent mean numbers of

larvae consumed; such sample means are, therefore, relative

rather than absolute indicators of the numbers of larvae

consumed by the different groups.

Intact G. punctipes under either light regime were

equally (differences not significant at p=0.05) able to

capture larvae, and (as previously stated), altered indi-

viduals under 14hL:10hD were at least as successful (p=0.01)

in taking larvae as were intact predators. This demon-

strated that the antennae are not necessary for the capture

of larvae, although they can be used in place of the eyes

to find larvae under the minimal search conditions of this

experiment. The importance of having at least 1 of those

2 sensory systems is evidenced by the fact that altered

individuals deprived of visual cues consumed fewer (p=0.01)


larvae than did intact Geocoris, and fewer (p=0.01) than

did altered individuals under 14hL:10hD.




Most members of the hemipteran family Lygaeidae

are phytophagous, and several, such as the chinch bug, are

important pests. In marked contrast, omnivory with heavy

emphasis on predation seems to characterize members of

the subfamily Geocorinae (based on observations of Geocoris

spp. and Hypogeocoris sp.) (Crocker, unpublished data).

Such a distinct ecological specialization makes the

Geocorinae an ideal group to study for niche-related mor-

phological specializations. Unfortunately, most present

literature treating the morphology of geocorines is

limited to the examination of characters for their

taxonomic value; Ashlock's (1957) description and illustra-

tion of the phallus of Germalus samoanus China and Hypo-

geocoris piceus (Say), Singh-Pruthi's (1925) illustrated

description of the genitalia of Geocoris thoracicus Fieber,

Jaczewski's (1926) and Piotrowski's (1950) studies of the

male genitalia of Geocoris ater (Fab.) and G. moderatus

Montandon are important contributions of that type. Al-

though I have not seen the papers, the study of the egg

and ovary of Piocoris erythrocephalus Lepeletier & Serville

by Xambeu (1904) and the investigation by Miyamoto (1957)

which reported the number of ovarioles in Geocoris proteus

Distant are probably also primarily taxonomic in nature.

Hutchinson (1944) reported that the spiracles on abdominal

segments 2-4 were dorsal, whereas those in segments 5-7 were

ventral in Geocoris uliginosus limbatus Stal, a positioning

sequence peculiar to its subfamily. The metathoracic wing

venation of Germalus sp. and of Geocoris uliginosus (Say) was

compared with that of other lygaeids by Slater and Hurlbutt

(1957) in an attempt to clarify our understanding of the

phylogeny of the Lygaeidae. In a paper that I have not been

able to trace down, Teodoro (1925) described the wing

coupling mechanism of Geocoris megacephalus mediterraneus


Only 3 papers actually deal with the internal mor-

phology of geocorines. Yanai and Iga (1956) reported that

43 percent of the midgut epithelial cells of Geocoris various

(Uhler) (1 specimen examined) were binucleate and that

the layout of the midgut of that species was of the "Hy-

drometra type." Pfaler-Collander (1941) found that

Geocoris lapponicus Zetterstedt and G. ater have a diploid

chromosome number of 20, and compared the karyotype of

these geocorines with those of other lygaeids. Schneider

(1940) reported finding symbiotic bacteria in the fat

tissue of Geocoris 9rylloides (L.).

In the present study, I examined the general dis-

position and gross morphology of the digestive, nervous,

and reproductive systems and the metathoracic stink glands

in the adult male Geocoris punctipes (Say) by microscopic

examination of serial sections of the entire body and

by dissection.

Results and Discussion

Horizontal serial sectioning (Table 13 and Figure

6) of an adult male Geocoris punctipes disclosed well-

developed optic lobes connected to the bug's prominent

eyes. In many sections, the surface area of the neuropile

in the optic lobes was subequal to that of the main body

of the protocerebrum. As is characteristic of Hemiptera,

the number of distinct ganglia in the ventral nerve cord

was reduced to 2, both of which were in the thorax.

My findings concerning the digestive tract of G.

punctipes are only in partial agreement with generalizations

made by Elson (1937). Elson depicted the alimentary tract

of predatory Hemiptera as being quite long (as much as

three times the body length), having a prominent "stomach,"

but with the remainder of the midgut being a long simple

tube except for the portion joining the ileum which is

sometimes dilated. The gut of G. punctipes (Fig. 7) bears

2 anterior chambers (Ml and M2), the second of which is

larger and corresponds to Elson's "stomach." Posterior to



Row Comments

1.1 Begins penetration of dorsum of thorax, and passes through
wings. Powerful longitudinal muscles dominate thoracic

1.2 Raised lateral rims of abdomen penetrated; 2 prominent, linear
objects medial in thorax (gut?)

2.1 Right, then left eye penetrated. Pair of muscles
medial and forward in head; salivary glands (?) fill much of
the space anterior to and above the protocerebrum (not visible
in these cuts).

2.2 Testes visible laterally in abdomen, long and slender, each
with 4 follicles. Dissection has disclosed that the roughly
banana-shaped testes (bright orange in life) are vertically
oriented and wrap partially around the midgut, conforming to
its shape. Protocerebrum and optic lobes with their neuropile
masses (lamina ganglonaris, medulla externa, and medulla
internal) evident; neuropile in optic lobes well developed,
with a cross-sectional area at least equal to that of the
central protocerebral neuropile in many sections. Gut fills
much of abdomen, 4 major chambers appear evident.

3.1 -Forward-most chamber of gut produced into esophagus, which
passes under the protocerebrum and between circumesophageal
connectives, which join to form the subesophageal ganglion.
Genital capsule (pygophore) evident. Principle salivary
glands evident mesally in thorax, extending longitudinally.
Ileum and rectum visible, especially in the final sections.

3.2 Metarhoracic stink glands mesal, with the points of their
V-shapes mesal. Heavy muscles running obliquely forward
from the back corners of the head connect mesally to the walls
of the pharynx. The origin of the beak is visible, as are
muscles emerging from the coxae.

4.1 The abdomen is dominated by 2 chambers of the gut and the
genital capsule; laterally, the testes are visible. The 2
metathoracic stink glands fuse medially. The sections pass
through the ventral limits of the head and thorax. In the
final sections, only the coxae and abdomen remain.

4.2 The sections pass through the ventral surface of the abdomen.


salivary gland?


*-'r : -:be

p-c: -. _- rebrum
ch:.-ri: ganglion II

thoracic ganglion I



genital capsule

Figure 6. A composite, semi-diagrammatic representation
of the major internal organs of an adult male
Geocoris punctipes.



Malpiqhian Pylorus
tubule ylorus
(not full

Figure 7. Digestive tract of Geocoris punctipes.

M2, the Geocoris gut is tubelike (M3) for a length about

equal to Ml + M2, after which a third chamber (M4?) sub-

equal to Ml occurs. The chamber I have tentatively dubbed

M4 immediately precedes the pylorus, a modest chamber

bearing 4 delicate and quite long malpighian tubules

(Fig. 7). The pylorus is "that portion joining the ileum

which is sometimes dilated," according to Elson. I was

unable to recover the gut posterior to the pylorus.

The horizontal sections of the Geocoris also

disclosed Ml and M2 (Table 13 and Figure 6). These sections

also revealed the path of the esophagus forward to the

pharynx. Heavy muscles originating in the posterior angles

of the head extend forward and mesally to the pharynx,

forming a pump that must be quite powerful. I have been

unable to establish clearly the path of the gut posterior

to M2 in the serial sections, although I have indicated

in Figure 6 those connections that seem to be present. In

summary, the alimentary canal of G. punctipes appears to

be more like that in Elson's Plate I (which depicts a

hypothetical and generalized hemipteran) than any other of

his models. The sole specializations in the Geocoris gut

were the absence (1) of gastric cecae and (2) of the tube-

like M5 segment of the gut, characteristics which Elson

associated with all Hemiptera that were either predatory

or omnivorous.

Salivary glands bearing a large principal lobe and

a more slender accessory lobe are usually found in the

thorax of Hemiptera (Elson 1937). I detected what seemed

to be salivary glands in the head and thorax of G. punctipes

(Table 13 and Figure 6). Further confirmation is needed.

The well-developed metathoracic stink glands

(Table 13 and Figure 6) are fused ventrally, but extend

dorsally as 2 lateral horns. Although Geocoris are small

insects, on the rare occasions that one of them has dis-

charged its stink in my presence, it has been my impression

that their discharge is perhaps more potent than that of

the southern green stink bug, Nezara viridula L. (Penta-

tomidae). Wigglesworth (1965) stated that the components

in the stink material of suborder Geocorisae (Hemiptera)

are 1 or more of the unsaturated aldehydes, hexanal, hep-

tanal, decanal, or the unsaturated hydrocarbon n-tridecene.

He said that these compounds are nerve poisons effective

against other insects, acting either as repellants against

predators or causing paralysis after entering via the


The testes (Table 13 and Figure 6) of G. punctipes

each apparently contain 4 follicles. The testes are

bright orange in life, and are loosely wrapped partially

around M2 from opposite directions, their banana-like

shape conforming generally to the bulge of M2 and their

proximal portion being ventral.


A major limiting factor in the analysis of this

material was the quality of the slides. Unidentified

sources of error resulted in slides which retained much

of the gross shapes of the tissues, but which contained

little recognizable cellular detail.



Formerly, the natural feeding habits of Geocoris

spp. had never been studied systematically except in

respect to the ability of Geocoris to attack or control

the populations of a few pest arthropods. Geocoris were

thought to be predators, although evidence indicated that

they had some ability to feed on plants and on dead


The present research was undertaken to clarify

our knowledge of the feeding niches of the 3 species of

Geocoris found in Florida: G. bullatus, G. punctipes, and

G. uliginosis. Field observations disclosed that these

3 species are omnivorous. They feed primarily upon small-

to-minute arthropods from a wide range of taxa, including

both active and sessile stages as their prey. Many of

their prey are at times serious pests, and Goocoris spp.

probably are important in their natural control.

A wide range of herbaceous angiosperms are nor-

mally fed on to a limited extent, even in the presence of

prey. The exact importance of this supplemental phyto-

phagy to Geocoris is still unknown. The third and least

important component of the feeding niches of these Geocoris

spp. is necrophagy; my data indicate that they occasionally

feed upon dead insects or fragments of insects that they


The breadth of the feeding niches of these Geocoris

indicates that they should be expected to show a functional

response to most changes in prey density. Numerical

responses would generally be expected only when the target

prey made up a considerable proportion of the total avail-

able prey in the habitat, in which case the predator would

be responding to changes in its total potential food supply.

Exceptions to the preceding might be taken as evidence of

differential preference for that prey. Although aphids,

thrips, mites, and a few other types of prey are commonly

taken by Geocoris spp., there is as yet no firm evidence

that any of these are especially preferred as prey.

Because of their great abundance in many crops and

because their predatory role is that of flexible general-

ists, Geocoris spp. probably are among the most important

groups of entomophagous arthropods. Because they do appear

to have slightly different habitat preferences, the im-

portance of particular species varies in different situations.

Geocoris punctipes use their eyes and antennae to

detect motile prey, but must depend on their antennae for

detection of immotile prey. This dual detection system allows

them to utilize extremely diverse prey, including visually

cryptic prey that are unavailable to hunters that must

rely on their eyes, and many other prey whose mobility

would protect them from hunters that depended completely

on contact. Such versatility greatly increases their

potential food-base, making them less vulnerable to fluc-

tuations in the availability of any particular prey types.

The internal anatomy of Geocoris includes at least

1 specialization for predation: the lack of gastric cecae.

The eyes and optic lobe of G. punctipes are well-developed,

as might be expected in a predator that depends heavily

upon vision. Geocoris are poorly suited for grappling with

a powerful adversary; well-developed metathoracic stink

glands are their only apparent defensive weapon. The

products of such glands in related Hemiptera are known to

be toxic to other insects. In most cases, Geocoris run,

fly, or hide from potential enemies.


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