Fruit-Tree Bark-Beetle (Scolytus Rugulosus Ratz.)


Material Information

Fruit-Tree Bark-Beetle (Scolytus Rugulosus Ratz.)
Physical Description:
Chittenden, F. H ( Frank Hurlbut ), 1858-1929
United States Dept. of Agriculture, Division of Entomology ( Washington, D.C )
Publication Date:

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Resource Identifier:
aleph - 29678756
oclc - 631045529
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Full Text

CIRCULAR No. 29, REVISED EDii ... I ay2 i.

United States I)epartmiCnT(iriiltuire
L, 0. HOWARD,-in I f'

THE t'RI IT-TRiEt; 11AR K-EEl'TI., l
.... ...*r i .. !;.|I,1 I ,''V -
II'. F. !1 I II111"1"% '! ,/ t V A ^' -- .'.**


Orchard trees are -iljic I to li attack 4f a -iinll h,,rill!Z in-,,, l11
fruit-it rev bark-beetle (Sci,'d ibi.; ,iilIis .'i IRatz.), its presence being
nmlinif,'stedl bY what are called "worm-hloles," niminute round iil'iiiL-,

af b e d

c, e itero ,,'1 iti p '',1

in li( outer bark -, an, .l\v a sixteenth of an inch in diameter, accom-
panied 1% wiit in.r of the leaves and -lri vlfii, hof the l'.irkl. ;' ii. in the
clase of 1t4,n'-frii I rvt-.. lM io1re or less co)pious exudationis ,f '11111i.
Tlhe ir-t ilppI,'ririi- hois are made Iy the parent beetles in ,r-It rinj,
th 1,,irk to di'p,-ii their g.,-. but later, if no tl'. 'rt is mide to ir'hk
the inect's "rk. the liirk will lit fiinI ilii kI "'pepperedI" vNith
hohle- as I h',iiI by till,, birdI shot. Tli,.-. are li, exit holes of beetles
that have il livir larval -t.i;i. mined and r1. ,1 p-l, under the bark.
holes are iilT iin.i' 1> M the m nature ii,,.t-, 1 7. 1r1.,I'.i li 'lli i,.h ilill'-, in
the latter dIa v. of a easn .ilit r midsulmmer, evidently f. r no other
purpo-, than for f, ,l. .A piecef twi_. -., -" in. exit holes in the bark
anid thlie ri f the Iinscts 1, ,.! it, is ro 'ln, iltcd in ligure 2.

The insect which causes this injury is a member of the Scolytide, a
family of cylindlrical bark-and-wood-boring beetles. The adult or
beetle is shown at figure 1, a. It is about one-tenth of an inch in
length and three times as lwng as wide; uniform black in color,
except the tips )f the elytra or wing-covers and a portion of the legs,
which are dull red. The punctuation of the thorax and of the elytra
is also illustrr:tmd and at b the peculiar form of the short abdomen is
shown. This insect is a European introduction and is sometimes
known as the sl(hot-burer, orchard scolytus, and fruit bark-beetle.
In Europe the species first attracted attention by its occurrence on
young apple trees in 1834; in the United St ates it was noticed for the
first time in 1877 through its inj u ry to peach. Available data indicate
that plum is more susceptible to attack than other trees, while peach,
cherry, and apple are attacked about equally. Pear is
also quite subject to infestation, and apricot, nectarine,
quince, mountain ash, and Juneberry trees also harbor
this species. In Europe mountain ash has been re-
corded by Diihner, and hawthorn and elm by
Eichho ff.
Two important factors that have operated in the
past have had a marked effect in increasing the num-
bers and consequent injury by this us well as other
afruit-tree borers: (1) The introduction of other de-
structive insects and diseases into many of the dis-
S tricts which this insect inhabits, which has undoubt-
/ edly, by weakening the trees, afforded opportunities
In' that would not otherwise have existed for the multi-
S plication of these borers; (2) severe wind-storms that
FIG. 2.-work of sco- often sweep through portions of the same region and
IItu8 rugtosus in which cause extensive destruction of fruit and other
twig of apple-
natural size (au- trees. The presence of the injured and dying trees
thor's illustration), that are permitted to remain is a st ;an dling menace to
the culture of stone fruit,, applles, and pears.
One source of injury that is too often disregarded by the fruit grower
is in permitting trees to remain after they are badly injured and use-
less for any practical purpose except as firewood.'
Until recently there was a difference of opinion as to whether or not
this species was able to breed in vigorous trees, some writers going so
SDr. E. F. Smith, of this Department, has on several occasions noticed infested
orchards in the vic init of wood yards or ,,f brush or remnants of abandoned orchards
three such instances are recorded by him aIulletI in 4, Division of Vegetable Pathology,
U. S. Dept. ._,'.. p. 30,. In two cases cited, "lj,.chi brush frin diseased trees had
been cut in the spring and piled near an .nr'-h.rd and in both the only attacked trees
were in the vicinity of those piles, and those most seriou-ly attacked were nearest to
[Cir. 29]

far as to assert that thIe beetles will Ut ack .inly levitalizd', grot 10
Asa rul., ,nly diseased tI rees or such as may already le 'il ii .' from
the attacks 'f other insects are permanent ly inj',... buIt apIiaently
,inmial trees are also attacked antid sometimes coiplctely t retver
withouI t assistance. ."%u n,4-fruiIt tI V-, especially itch, if in co-l i-
tiiiL. exule such quantities of gumi that the beetles are repelled anmd
i linIIII,, their bMtrrows without iiiiil1 to iny extenlt under tIhe lark
or dvpoit ill--, their eggs. As ,' s there is a vig orous flow o)f saI
there i little dlnger 4f serious injury, biut after frequent attempts to
,l)litin lodgm,,ent the beetles mn/ay so "bleed" a tree lli.,ilin course oif
time. tMey are able to attain their |ii i,..... when the d1eati ()f tlie
tree is assured.
AnotheWr form of injii rv is the destructition, at the l>(,'iTLiIiL'_ of spi in',
,f sinuill I \ i-, ,','li her with the leaves which they bear. The beetles
are also reported to destroy leaves by l,>riiiL into the base ,'f thle
buids at thlei axils.
injirv, th,'',, is mainly due to beetles of the first generation iiil-
upon the terminal twigs in piriiir and afterwards of later generations
on the trunks and ,l erai,, limbs of trees.
In common with most diurnal species this insect is found more
abundantly on the ip.,i'd sunny side of living ti,,.- which !,,ii.i
drier would exude less sap, and for that reason i)e Illore' available as

From its first center of iIntroduction in the I'nited whether
central Nw York or elsewhere, this species had p-,.;id. presumably
in tilie main by the distribution of nursery v-ltk. from infested to
uninfected it rinets miiitil. three years .lftr its first observed occur-
rence in 1%77, it was reported as injurious in localities in Nv. Jersey
i'en II.-iViiiii. M.i-,iri. Ma r\ln id. and the I)istrict ,f Columbia.
In the sU'ic,,ediiui," five .vI'.s it was reported successively from Masisa
chuseltts, \ irini.i. Geor-ia. and South Carolina, indicate il.: a w ide
distribution at that time. In I'-,, it was br,,u,,Ii; to the attention
of Dr. S. A. Forbes by its depredations in the State of Illinois. and as
a consequence was given special study in that State.
SThe writer and others have on several Xoccasions sTn k iach tree f that wer appar-
.tlyv fre from disease and itfr ,iii, insects other than the fruit-tree bark-beetle In 1IK1
i'.I h orchard, where the beetles were just b', ,.ir,,% i,. attack in i, Ii ,, .1. ri !
311 the inftedI trees were, to ,,,' r appearance, perfectly health. in a tI. 1e tree
that IIk' ,ll. wa scarcely at all .1:1-. ,., ..liii.. a i, .i1i. .ri tree that .I -ked
ikh.1,luely sound was well covered with the beet leTi and their bIrrw. Mr. I'.- -
I'to. lren. who has Air,.iill' observed this species in \1. -r:..,i,.r. ,,, Pa, ha-
noticed a precisely similar condition of affairs at TTii.t .11 V"o 5,1 and Mr. W V P
i',,r-a. .if the Division 4i r.' iP,,, has witne 1ed the name at M ilf+rd. I el and PrI, f
E. A. P p'n.k" ih. sanme in Karna. 1., l-tl I' 1 PIi. EntI, p. Sr: al.- I e,
l11l 1\ ,0 N. Y. .%,I itI;ei.ia Eql\ :i.> pp. l122 1-
*S 'eiireeniili Rept. 291r Ent Illin.i, f.r i-' and i' i ',L I pp. 1 >.
fir 29)

A plerusal of the list of localities in which this species is known to
occur in the United States shows that it is an inhabitant of the
Upper Austral life zone, and that it is now resident in nearly every
State of the Carolinian division, as well as in a few that lie within the
Transition zone. This includes territory from Massachusetts, New
York, and Mi.liig;.n in the Noirth to Alabama and Georgia in the
South, and Missiiri and Arkansas in the West, a total of nineteen
States and one Territory in which it has been reported to occur in
injuriii, abundance in one or more known localities.

As early as the middle of March, first of April or later in May, ac-
cordiniig to locality and season, the parent
F.1 j' 'beetles make their first appearance of the
1 year, and may be seen crawling about
r- orchard trees and beginning to burrow
Through the bark. After penetrating to
--CL thesapwood, feeding as she goes, the female
constructs, partly within the bark and
p, pa y in the wood next to it, a vertical gal-
i-^- l]er or brood chamber, and along the sides
of this at very short intervals gnaws little
pockets in which she deposits her eggs.
SThe minute, whitish, grub-like larva hatch-
'' K ing from these eggs,, excavate little side
c galleries, which start out at right angles to
1 the brood chamber but soon diverge and
widen with the increase in size of the grow-
ing larva. Mutchl more frequently this
'b insect lives in such numbers, with its gal-
FIG. 3.-Galleries of ScolyIus rugu- leries so closely pmaiked together under the
loss on twig under bark; aa,, i bark of a tree, that it is with difficulty
galleries; b, b, side or larval galleries;
c, c, pupal cells-natural size (after that individual galleries can be distin-
Ratzeburg). guislLd.. A specimen of the insects' work
on the wood, shown at figure 3, illustrates the cr, ssing and recrossing
of the galleries of different larvwe. Completed main galleries measure
from one-half to two inches in length, and the av%-rigc number of eggs
deposited in each by a single female is said to be about eighty.
The parent beetle, according to the studies of Dr. J. B. Smith at New
Brunswick, N. J., occupies less than a week in the construction of the
brood chamber, the eggs hatch within three days, and the larva is
about twenty dlays in at training maturity. The fuill-grown larva, shown
in natural curved position at figure 1, d, is white in c. ,lo, with a small
[Cir. 29]


yell, iIi hemdI and Imron i, min,,Ii, and its surface i, IlItl(-Ii w inkhe1-.
i WVl 2' 1 about) to t i r, t iun. the larv for isI at 1:te c,, enlid ,' its i ..-l-
ler-v an oval chamber, usually in thlie \",,I. -Int ione ioeillc Jit ily in
Ilie 1lilk, and here the lpuplal ..,' is asts Ti pe)ri1od ff the
plIpl,, state ats lsr'Ived in moderate weat hIer, at W i-liiii,:toln, I). ('.,
is seven da'.: in cooler weatiier of d'r i' auttm n tin lis Ini v Ie ex-
tended to ten da Hs. .\A11,1% i:., f,'-r both the shorter aind Iiir,,i periods
in the ,e,.f.Ipiiinl ,f the |ir'l,.iriattory -,i '-. whicth must exist in
til' diirtiil e tteilpi ;ll lires of mIllidsumunI(er, autiInlli and swil Nrir.- we
have iipplrxiiiiit elvi li,.f cycle 'f four t)o s)ix or plintrhlS mone weeks.
The earlier writeers on the fruit-t -, lirk-l-eet I to k lit Ie account of
itsi dev1ri.,11 I un. evidently l -ii- of thle opinion liit, it re quirret 1i veitr
to attain rn il iiil it v. Tii-.. Seliiiio.lli-' i,\ ii ini in 1 i., states thalt in
mnik- of It,1iin apple trees the lirva' fed till late in atumn lnd N the
beetles were seen lliii confinelment) I tlbout t lie cind of 4Fveruarv at rest
in iheir in>,i-i_'i'. which they iAri in April a=i May. (o miraiu, \wri iii.-
in Il S6 l, s- thIat Ilarva m'(,, their I r, Ii b)y th mid i dlde of \\i iitr,
punipiite the last -f M.,y, and mature in .Junle. It will he seenll tlat
these two authors hlad no conception of nuorne him i i' l generat ion
aninuil I Later writers have assumed lte prohihbilitr of aI second
gener Ii, 'lii Prof. F. N WXebster, :.l'p.ikii of its oclurrTrieve ill ('cen-
tral Ohio, -;i- "''the species is double-brooded." I
Ohsrrt ii in., conducted in the vicinity of the District of ('olumnbia
hlai've led the writer to the belief that there may hie a thi tird venerationi
prodlucvel in this latitude While the life cycle ma i e I passed in as
short a space ias four w\'vk-. it would :]|i[..r that lie beetle is sone
tie in ex.a ;ilinL from the wood aind in fe'iiia- before conmplh ii.v tlie
prniiry g':ilerie, iil and hiyiNi _, its _'

i Ant. I, li i ihi., i Iort. So I-'', ,-'... pp. l '1 I-
S-'r.niii a twig"i *I |ll .. ti iii.:I larvNa anti procn ured 1b% ti(, t riter in ith it iii.
of ihIl. 1 ri, I i Colunbia in pi nil". r the earliest individui als i l the tirt .. r.i -
tion were obtained 'I1.,. I of the I 'ear f 11.'. ii, fVhat wI :i.,. e Insid r the second
gpti1'r.i i. Ii i--iiin- from the bark of plum the tir"t week of .iil larve were then
pre->,nl i) L'r',.1i. r ablindance than at .111'. other -ti.,.. y th I Ios.e o.f the mIonth all
buin an extremely small ,-.r 'i ti.i n had iWued as beetle., a few -'F :-j.l: |n|p>U andt
still fiw.r lar, a I- in-. present under the bark, which wa. then hilne oinb'l bI the
mull il hile"i' .thi insci't which it had harbored l .'u I. ill all thebe.etles pealped,
as he wood was quite dry and no longer in contlition for thelr maintenan e A. third
g,'niratliii. i previous sitrmte are, correct, wa< reared the 7 ir. t two we, ks 'of . >. 'i in-
ber from a ,liffi rii lot .i p1lum branches and was observed al t the sAame pTeri- l in a
preach orchard in .iinlh,.r locality, In the latter place the beetles had e ilIntly been
at work e\ 'mnl days, h.i in-. made holes -'illi, i nil ', deep in the tree. for their complete
eoncealmeent. Indications were that this hy 1pothetical third -:.'. rifit ..i made no
atlempl to breed but n,.r-.l' entered the peal h trees for foodt andl shelter. I'..1'1 '-
ri,,il l oe seen I|rj,. I ini.. from their burrows as late as- the I'-' wek of No ember,
but no i-all'ri'',- ,l ariv kind were to be found.
[i Ir 291

In the extreme South, according to Mr. C. F. Baker, who has ob-
served this species at Auburn, Ala., it is almost impossible to trace any
broods, owing to an apparent continuous breeding through the spring,
summer, and fall. As late as December females were found in newly
formed brood chambers. Larvae were also observed at this time and
the opinion was expressed that "the insect must pass the winter in
both ,L', and larval stages."


A much greater amount of damage from this bark-beetle would
result were it not held in check by a host of natural enemies. Inii
Europe two hymenopterous parasites 1 destroy it in great numbers.
In the United( States several other parasites have been reared from
or with it.2 In additionn, three or four pre-
( daceous insects 3 have been detected under
circumstances to indicate that they lived
upon the bark-beetle larvae.
cSome idea of the value of these parasites
-I'- in helping to restrain the excessive multi-
plication of their host may be had when it is
stated that in a case that recently came
S t under the writer's observation at Washing-
Fio. 4.- Chiropach ys colon-much en- ton, 92 parasites were reared from infested
larged (author's fihiiLra! ,on.[,,"p rsie eeraedio rse
argd (author'stwigs, ag;i int 72 beetles. All but two in-

dividuals of the parasites were Cir,,parni i.;s colon (fig. 4).


Borers are among the most troublesome insects with which the fruit-
tree grower has to deil, and the present species is. perhaps, the most
difficult one to control by ordinary measures. Tihe time-worn
remedy of cutting borers from the I rev. valuable for large forms, and
still practiced many ,-spiI,,. is useless ,;iiinit the fruit-tree
bark-beetle. Preventive measures that muv be successfully used
against other boring species are also ineffectual. The main diffi-
culties in the way of t rt',inig this species are its minute size, its
extreme abundance, and thle fact that it is not restricted to any
1 Bi. i. fuscipess Gour., and I',l,,.n.t bimaculatus Nr-'.
2 Chiropachys colon Linn., Raphitelus mnaculatus Walk., Eurytoma bicolor \\alh,
Eurytoma cras.sineum Ashm., If,/ ,i niia unica Cook, Hemiteles scolyli Ashm., Platilgrr-
rhus (?) scolyti A.hrn Tetrastichus scolyti Ashm. "i .. ndar. ), and two or more new
species of Euipeihnu-
,3 P'ylloboii ,.s dislocatus Say, '1 rus ich neunmoneus I'la i, 7 a',ii-.n ,ro, :I. .i i unknown
clerid larva, h'l,:iftl,,iiis bipunctatus Say. The American species have mostly been
reported by D)r. A. D. Hopkins and the writer.
I Cir. 29) 1

prtion of a tree, aind that uipo'sitiom o 'curs i'i.. lically tl ..ii .it,'li.iij
the cutire season.
('/,1 n culthitu is cleanly cultural practice; in -'.,'t, little 1 f really substantial i I lii
(an be accomplish he I N ith IuI t it Btrushwool i and other rehtn ts of
mr ha.,ini-. as hlus already been shown. are too t i rii'uli Iv hleft, lo serve as
centrsf t f iufest at ion to ssodil trees. As s o)n as infested trees arc
seen to be 1i'i1.kll\ d ii-:. it is p iracticdliy useless to do) anyl Iii,- to
save them. Tr,.,- may recover from slight attacks, aud tlHe fruit-
tr',,wer must use jiidLiii'lnl in distcriminatii|,-- between whilt %ill recu-
perate and what are be o1nd hlopc of reco very. 1, ml shPuh l clut 1t and
1i) i11 the ,lviiiL a d dead L,'r,, ,lhi us (fteu a-s et ecte(i.
For the 1,'r,' t ]ii, election o(f one kind of fruit tree Iall other kinds
which ,iir, pernianently injured must be dcstr yed. If. for any r,.i ii.
such measures We i,._,irteid dluiiii' tite suthnur, the injured *_'"i.I
should at least be burned before tie, fll,,mi. -|'in_, :;s l) suhel
means il the hiherua1lit, insects ill be dic-

Tn eonnIleetio( withi tiese ii(sUtr'tI if -',.. '.y/ if
orchard trees be kept in i_''rou,, lie-ilthl _- .
with the aid of manure or mineral fei lit,. '' -i.
if necessary they will more readily be able r, .\
to withllstnd hlborer attack. t
f, cl,4i 1 ;.,rib/rri rs.Newspapers, tarred
palpin, burlnp, or straw \[i:,l]',d about 1t+ .- "p+"+ +ri,
t+i* ilh it ;l -Zueh a nIl i II wi th
ti-uniki and limhs deter ,,,iii i,. insects from +,>iiur t+ I. i. n a ig r d v
layIvin, their e,,L", upon the tIrees nt tlies(e ..e
poinlis; but mechanical )ireventives can not well Ihe applied ex.-li
to the trunks and Ii'il Ii branclhes, whence poisotnous washes a nd like
substances are piil'i il:le.
Ih ri,, ,,t wiu'a,'hf and ,1ii,,, Hrt td in ( .,. ,. il w itslie are' in use
n.ainh.It borents ,f t his nature ()ne A ,f the-e is- an alkMline wash pre-
prIel of soft soap reduced tO JtI consistent of thick lai'nt by ad'liir-
wa.hin,.. soda in water. Another is repreed1 0f one pint df ciruhe car-
boli' acid, one -a.,Iri of soft soap. and diluted w! ith .Lil, t _lhns -4. *
water. Te.,. washes should be appliedI tl,,,,,,-dilvy, pleferahlv with
a brush, care 1iii.' taken to cover all po rtions of I the trunk and
a.s many branches as possi|ie,. It should lie retmemierheild that they
are ..itlply preventive alnd do not kill the borers or iw lord anym pro-
tectiomn If'Oin injury by them if once tl!e insects I ha e en tereld lie tree.
So,,,me _'riiid, of fi'.li-Ol and whliale-oil soap a;re v:luahule ;s deter-
rent-.hut do not entirely prevent tlhe insects from i--, i .fr lite trees.
With any local application that lmv t e ma1de ,i.'st this bark-
beetle there is always this 11 il, itli that ti' tv w _- lipt -),.i!, limbs
[Cir 2,1

can not be completely covered and the beetles readily enter them,
hence the necessity of the most careful inspection during the season
and the cuttingg out of the badly infested portions.
Whatever deterrent is used should be applied just before the first
warm days of spring; in the Gulf States, before the first of March; in
the latitude of PeiinYvlv:iiiii and New Jersey, by the first of April.
Owing to the development of so many generations of this insect it is
necessary that applications be renewed during_ the season.
Cli.lliig.-It is probable that the European custom of girdling, or
"ringing," a few trees in an orchard as traps for such beetles asmay
not have been (hd.etr'ivil with their host trees might prove effective,
but, although the remedy has frequently been recommended, we
have no knowledge of its successful use in this country.
Trap trees and branches.-After the issuance of the first edition of
the present circular (MAarch 25, 1sgs,) it occurred to the writer that
much injury might be avoided by the judicious use of dead wood to
decoy the beetles for oviposition. This remedy has already been
advised for the flat-headed apple-tree borer, l)ut, so far as the writer
knows, it has not been given a fair test as to its usefulness. Freshly-
killed host trees, branches of smaller limbs of the same, such as
ordinary prunings, should be placed about the orchard where infesta-
tion is most feared. Apple and pear would probably prove most
useful for the purpose because apparently most favored by the borer.
In the application of this remedy it is essential that the operator shall
know the dates of the first appearance of the different broods of the
bark-beetle in his particular locality.
Left about the orchard as previously h..scrilil. the decoy material
will attract the beetles,., appearing (in the District of Columbia) in late
March and April, and after they have deposited the bulk of their eggs
it should be destroveil by burning, say, four or five weeks after the
beetles first appear, to prevent the dNevelopiing of other generations,
and a new lot of branches should be provided by pruning injured or
superfluous material to attract the next generation of beetles, which
appears about the first of July. The last-appearing beetles, which
are active about the first of September, must be trapped agliin in the
same manner. The greatest care should be used in all cases to destroy
trap and other infested material before the issuance of the beetles.
Considering the efficacy of parasites in the control of this insect, it
might be found valuable to inclose pieces of infested branches in boxes
or barrels covered with wire netting of a mesh sufficiently fine to pre-
vent the beetles from issuing, but to allow the parasites to make their
exit and thus to keep up their good work in the control of the pest.
Kerosene; creosote oil.-The beetles may be killed and much con-
sequent diiniige prevented if they are detected at the outset of attack,
[Cir. 29]

by In Iiin. lehtl te infected -i ,,l-. fiiii which tie1 11111 or sap hlls
beviwm to ooe. w it i a small .iI.'' sat Urated w it iI ker'(oeme, (*r csnte
oil. or turpentimne, aid fstfnIeml at tiv end a stick or pole. After \ilil, the beetles inll this iimanner upon a tree, it nmay be I 1-
tected from furt her attack i by p:ip wr1.l %Iipi'-., iiiil should it slo w
signi, of serious injury, this I,,i 'lit be nav crted, if hlie tree he too dry, by
ft-<[iil' wTit i li- _'- where this 0 an con'v encntly be done, to thIe bhase
of the trunk.
J\M t Wi~aON.
ScI'td' it .
W A.lIr <. I 1"'Ir 201

II 262111111111111111 BIIII 1 11111111 I II
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