Title: Beneficial insects and mites
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I01 Flo% c,


UNIVERSITY OF

FLORIDA

EXTENSION
Institute of Food and Agricultural Sciences

Beneficial Insects and Mites1
T. Henn, R. Weinzierl and P. G. Koehler2

Many insects and related arthropods perform
functions that are directly or indirectly beneficial to
humans. They pollinate plants, contribute to the
decay of organic matter and the cycling of soil
nutrients, and attack other insects and mites that are
considered to be pests. Only a very small percentage
of over one-million known species of insects are
pests. Although all the remaining non-pest species
might be considered beneficial because they play
important roles in the environment, the beneficial
insects and mites used in pest management are
natural enemies of pest species. A natural enemy
may be a predator, a parasitoid, or a competitor.

Predators, Parasitoids, And
Competitors

Predators

Predaceous insects and mites function much like
other predaceous animals. They consume
several-to-many prey over the course of their
development, they are free living, and they are
usually as big or bigger than their prey. Some
predators, including certain syrphid flies and the
common green lacewing, are predaceous only as
larvae; other lace wing species, lady beetle, ground
beetles, and mantids are predaceous as immatures


ENY-276


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and adults. Predators may be generalists, feeding on
a wide variety of prey, or specialists, feeding on only
one or a few related species. Common predators
include lady beetles, rove beetles, many ground
beetles, lacewings, true bugs such as Podisus and
Orius, syrphid fly larvae, mantids, spiders, and mites
such as Phytoseiulus and Amblyseius.

Parasitoids

Parasitoid means parasitelike. Although
parasitoids are similar to true parasites, they differ in
important ways. True parasites are generally much
smaller than their hosts. As they develop, parasites
usually weaken but rarely kill their hosts. In
contrast, many parasitoids are almost the same size
as their hosts, and their development always kills the
host insect. Although parasitoids are sometimes
called parasites or parasitic insects, these terms are
not completely accurate. In contrast to predators,
parasitoids develop on or within a single host during
the course of their development.

The life cycles of parasitoids are quite unusual
(Figure 1). In general, an adult parasitoid deposits
one or more eggs into or onto the body of a host
insect or somewhere in the host habitat. The larva
that hatches from each egg feeds internally or


1. This document was originally published as Circular 1298 by the Office of Agricultural Entomology, University of Illinois at Urbana-Champaign. This
document is ENY-276, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida. Publication data: July 1995. Revised: September 1999. Please visit the EDIS Website at
http://edis.ifas.ufl.edu.
2. T. Henn, R. Weinzierl, Office of Agricultural Entomology, University of Illinois, Urbana, IL; and P. G. Koehler, professor, Entomology and Nematology
Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

The Institute of Food and Agricultural Sciences is an equal opportunitylaffirmative action employer authorized to provide research, educational
information and other services only to Individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.
For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative
Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean.


I


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Beneficial Insects and Mites 2


externally on the host's tissues and body fluids,
consuming it slowly; the host remains alive during
the early stages of the parasitoid's development.
Late in development, the host dies and the parasitoid
pupates inside or outside of the host's body. The
adult parasitoid later emerges from the dead host or
from a cocoon nearby.

Most parasitoids are highly host-specific, laying
their eggs on or into a single developmental stage of
only one or a few closely related host species. They
are often described in terms of the host stages)
within which they develop. For example, there are
egg parasitoids, larval parasitoids, larval-pupal
parasitoids (eggs are place on or into the larval stage
of the host, and the host pupates before it dies),
pupal parasitoids, and a few species that parasitize
adult insects.

The vast majority of parasitoids are
small-to-minute wasps that do not sting humans or
other animals. Certain species of flies and beetles
also are parasitoids. Trichogramma, Encarsia,
Muscidifurax, Spalangia, and Bracon are some of the
more important parasitoids studied or used in
agricultural systems.

Competitors

Competitors are often overlooked in discussions
of natural enemies, perhaps because many
competitors of common crop pests also are pests
themselves. Competitors can be beneficial, however,
in instances where they compete with a nondamaging
stage of a pest species. For example, dung beetles in
the genera Onthophagus and Aphodius break up cow
pats in pastures as they prepare dung to feed their
larvae. This action speeds the drying of dung and
makes it less suitable for the development of the
larval stages of horn flies, face flies, and other pest
flies. Some nonpest flies also develop in pasture
dung and compete with pest species for the resources
it provides. Despite these and a few other examples,
the use of competitors in pest management is not
common.

Types Of Biological Control

Biological control, sometimes referred to as
biocontrol, is the use of predators, parasitoids,


competitors, and pathogens to control pests. In
biological control, natural enemies are released,
managed, or manipulated by humans. Without
human intervention, however, natural enemies exert
some degree of control on most pest populations.
This ongoing, naturally occurring process is termed
biotic natural control. Applied biological control
produces only a small portion of the total benefits
provided by the many natural enemies of pests.

There are three basic approaches to the use of
predators, parasitoids, and competitors in insect
management. These approaches are (1) classical
biological control--the importation and
establishment of foreign natural enemies; (2)
conservation--the preservation of naturally
occurring beneficial; and (3) augmentation--the
inundative or inoculative release of natural enemies
to increase their existing population levels. Broad
definitions of biological control sometimes include
the use of products of living organisms (such as
purified microbial toxins, plant-derived chemicals,
pheromones, etc.) for pest management. Although
these products are biological in origin, their use
differs considerably from that of traditional
biological control agents.

Classical Biological Control

Importing natural enemies from abroad is an
important step in pest management in part because
many pest insects in the United States and elsewhere
were originally introduced from other countries.

Accidental introductions of foreign pests have
occurred throughout the world as a result of
centuries of immigration and trade. Although the
foreign origins of a few recently introduced pests
such as the Asian tiger mosquito, Russian wheat
aphid, and Mediterranean fruit fly are often noted in
news stories, many insects long considered to be
serious pests in this country are also foreign in origin.
Examples of such pests include the gypsy moth,
European corn borer, Japanese beetle, several scale
insects and aphids, horn fly, face fly, and many
stored-product beetles. In their native habitats some
of these pests cause little damage because their
natural enemies keep them in check. In their new
habitats, however, the same set of natural enemies
does not exist, and the pests pose more serious






Beneficial Insects and Mites 3


emerging adult parasitoid
parasitoid larva parasitoid pupa aphid mummy




A B C D


Figure 1. Generalized life cycle of an aphid parasitoid. A) Adult parasitoid wasp injects an egg into a live aphid. B) The
parasitoid larva feeds within the aphid; late in the parasitoid's development the aphid dies. C) The parasitoid pupates within
the enlarged, dry shell of the dead aphid. D) The new adult parasitoid cuts an exit hole in the back of the aphid and flies
away, leaving behind the empty "aphid mummy."


problems. Importing and establishing their native
natural enemies can help to suppress populations of
these pests.

Importation typically begins with the
exploration of a pest's native habitat and the
collection of one or several species of its natural
enemies. These foreign beneficial are held in
quarantine and tested to ensure that they themselves
will not become pests. They are then reared in
laboratory facilities and released in the pest's habitat
until one or more species become established.
Successfully established beneficial may moderate
pest populations permanently and at no additional
cost if they are not eliminated by pesticides or by
disruption of essential habitats.

Importation of natural enemies has produced
many successes. An early success was the
introduction of the Vedalia beetle, Rodolia
cardinalis, into California in 1889 for the control of
cottony cushion scale on citrus. For over 100 years
this predaceous lady beetle from Australia has
remained an important natural enemy in California
citrus groves.

Although the importation of new natural
enemies is important to farmers, gardeners, and
others who practice pest management, the scope of
successful introduction projects (involving
considerable expertise, foreign exploration,
quarantine, mass rearing, and persistence through
many failures) is so great that only government
agencies commonly conduct such efforts.
Introducing foreign species is not a project for the
commercial farmer or home gardener.


Conservation

Conserving natural enemies is often the most
important factor in increasing the impact of
biological control on pest populations. Conserving
or encouraging natural enemies is important because
a great number of beneficial species exist naturally
and help to regulate pest densities. Among the
practices that conserve and favor increases in
populations of natural enemies are the following:
(1) Recognizing beneficial insects. Learning to
distinguish between pests and beneficial insects and
mites is the first step in determining whether or not
control is necessary. This circular provides general
illustrations of several predators and parasitoids.
Picture sheets available from the University of
Florida feature common pests of many crops and
sites. Insect field guides are useful for general
identification of common species (see Borror and
White, 1970). (2) Minimizing insecticide
applications. Most insecticides kill predators and
parasitoids along with pests. In many instances
natural enemies are more susceptible than pests to
commonly used insecticides. Treating gardens or
crops only when pest populations are great enough to
cause appreciable damage or when levels exeed
established economic thresholds minimizes
unnecessary reductions in populations of beneficial
insects. (3) Using selective insecticides or using
insecticides in a selective manner. Several
insecticides are toxic only to specific pests and are
not directly harmful to beneficial. For example,
microbial insecticides containing different strains of
the bacterium Bacillus thuringiensis (Bt), are toxic
only to caterpillars, certain beetles, or certain






Beneficial Insects and Mites 4


mosquito and black fly larvae. Other microbial
insecticides offer varying degrees of selectivity.

Other insecticides that function as stomach
poisons, such as the plant-derived compound ryania,
do not directly harm predators or parasitoids because
these compounds are toxic only when ingested along
with treated foliage. Insecticides that must be
applied directly to the target insect or that break
down quickly on treated surfaces (such as natural
pyrethrins or insecticidal soaps) also kill fewer
beneficial. Leaving certain areas unsprayed or
altering application methods can also favor survival
of beneficial. For example, spraying alternate
middles of grove rows, followed by treating the
opposite sides of the trees a few days later, allows
survival and dispersal of predatory mites and other
natural enemies and helps to maintain their impact on
pest populations. (4) Maintaining ground covers,
standing crops, and crop residues. Many natural
enemies require the protection offered by vegetation
to survive. Ground covers supply prey, pollen, and
nectar (important foods for certain adult predators
and parasitoids), and some degree of protection from
weather. Most studies show greater numbers of
natural enemies in no-till and reduced tillage
cropping systems. In addition, some natural enemies
migrate from woodlots, fencerows, and other
noncrop areas to cultivated fields each spring.
Preserving such uncultivated areas contributes to
natural biological control.

Maintaining standing crops also favors the
survival of natural enemies. Where entire fields are
cut, natural enemies must emigrate or perish.
Alternate strip cutting (with time for regrowth
between the alternate cutting dates) allows dispersal
between strips so that natural enemies remain in the
field and help to limit later outbreaks of pests. (5)
Providing pollen and nectar sources or other
supplemental foods. Adults of certain parasitic
wasps and predators feed on pollen and nectar.
Plants with very small flowers are the best nectar
sources for small parasitoids and are also suitable for
larger predators. Seed mixes of flowering plants
intended to attract and nourish beneficial insects are
sold at garden centers and through mail order
catalogs. Although no published data document the
effectiveness of particular commercial mixes, these


flower blends probably encourage a variety of
natural enemies. The presence of flowering weeds in
and around fields may also favor natural enemies.

Artificial food supplements containing yeast,
whey proteins, and sugars may attract or concentrate
adult lacewings, lady beetles, and syrphid flies. As
adults these insects normally feed on pollen, nectar,
and honeydew (the sugary, amino acid-rich
secretions from aphids or scale insects), and they
may require these foods for egg production. Lady
beetles are predaceous as adults, but some species eat
pollen and nectar when aphids or other suitable prey
are unavailable. The proteins and sugars in artificial
foods provide enough nutrients for some species to
produce eggs in the absence of abundant prey.
Wheast, BugPro, and Bug Chow are a few of the
artificial foods available from suppliers of natural
enemies.

The practices listed above must be judged
according to their impacts on pest populations as well
as their effects on natural enemies. Practices that
favor natural enemies may or may not lessen overall
pest loads or result in acceptable yields. For
example, reduced tillage favors beneficial but also
contributes to infestations of such pests as the
common stalk borer and European corn borer in corn.
Moreover, tillage decisions may be influenced more
by soil erosion and crop performance concerns than
by impacts on pests or natural enemies. Flower
blends and flowering weeds can serve as nectar
sources for moths (the adult forms of cutworms,
armyworms, and other caterpillar pests) as well as
beneficial. The ultimate goal of conserving natural
enemies is to limit pest problems and damage to
crops, rather than simply to increase numbers of
predators or parasitoids. Pest densities and crop
performance are factors that must be included in any
evaluation of the effectiveness of natural enemy
conservation efforts.

Augmentation

Augmentation involves releasing natural
enemies into areas where they are absent or exist at
densities too low to provide effective levels of
biological control. The beneficial insects or mites
used in such releases are usually purchased from a
commercial insectary (insect rearing facility) and






Beneficial Insects and Mites 5


shipped in an inactive stage (eggs, pupae, or chilled
adults) ready for placement into the habitat of the
target pest. Augmentation is broadly divided into
two categories, inoculative releases and inundative
releases.

Inoculative releases involve relatively low
numbers of natural enemies, and are intended to
inoculate or an area with beneficial insects that will
reproduce. As the natural enemies increase in
number, they suppress pest populations for an
extended period. They may limit pest populations
over an entire season (or longer) or until climatic
conditions or a lack of prey results in population
collapse. Generally only one or two inoculative
releases are made in a single season.

In contrast, inundative releases involve large
numbers of natural enemies that are intended to
overwhelm and rapidly reduce pest populations.
Such releases may or may not result in
season-long establishment of natural enemies in the
release area. Inundative releases that do not result in
season-long establishment are the most expensive
way to employ natural enemies because the costs of
rearing and transporting large numbers of insects
produce only short-term benefits. Such releases are
usually most appropriate against pests that undergo
only one or two generations per year.

The distinction between inoculative and
inundative releases is not absolute. Many programs
attempt to blend long-term establishment with
short-term results. In addition, conservation and
augmentation may be used together in a variety of
ways to produce the best results.

Insects and Mites Available for
Purchase and Release: A Selected
List

The beneficial insects and mites discussed below
may be purchased from insectaries or gardening and
farming supply outlets. Suppliers of Beneficial
Organisms in North America, a booklet available
from the California Department of Food and
Agriculture (see References), contains a list of
suppliers.


Predators

The Convergent Lady Beetle, Hippodamia
convergens

The convergent lady beetle (Figure 2) is one of
the best known of all insect natural enemies. The
adult beetle has orange wing covers, usually with 6
small black spots on each side. The beetle's
pronotum (the shieldlike plate often mistaken for the
head) is black with white margins and two diagonal
white dashes.
head

Spronotum




A B C

Figure 2. The convergent lady beetle, Hippodamia
convergens. A) Larva. B) Pupa. C) Adult.

These "convergent" dashes give this lady beetle
is a soft bodied, alligator-shaped larva. It is grey and
orange and is covered with rows of raised black spots.

Larval and adult convergent lady beetle feed
primarily on aphids. Where aphids are not available,
they may feed on scale insects, other small,
soft-bodied insect larvae, insect eggs, and mites.
Adults also feed occasionally on nectar, pollen, and
honeydew (the sugary secretions of aphids, scales,
and other sucking insects). Development from egg to
adult takes 2 to 3 weeks, and adults live for several
weeks to several months, depending on location and
time of year.

The convergent lady beetle occurs naturally
throughout much of North America. Adult beetles
overwinter in small groups beneath bark or in other
protected sites. In California, adult beetles
overwinter in huge aggregations in the foothills of
the central and southern mountain ranges. These
California beetles are harvested from their
overwintering sites, stored at cool temperatures to
maintain their dormant state, and shipped to
customers in the spring and summer for release in
gardens or crops.






Beneficial Insects and Mites 6


A common problem that limits the usefulness of
convergent lady beetles is that they fly away soon
after being released. In California, when convergent
lady beetles emerge from their overwintering sites in
the foothills, they disperse, seeking feeding and
reproduction sites where aphids or some other
suitable prey are abundant. Convergent lady beetles
harvested in California and released in gardens retain
this natural tendency to disperse, making them
poorly suited for small-scale releases. Field-scale or
community-wide releases of convergent lady beetles
for control of heavy aphid outbreaks are likely to be
more useful than backyard garden releases for control
of minor pest problems.

Convergent lady beetles provide long-term,
adequate aphid control in a release area only if they
reproduce. Several factors influence reproduction.
Adult female beetles harvested from overwintering
sites cannot produce eggs until they have fed on prey.
In addition, they lay their eggs only where prey are
abundant enough to sustain the resulting larvae.
Because adults are able to fly, they tend to disperse in
search of more abundant prey when aphid
populations fall below a critical threshold. If they
disperse without laying eggs, the aphids that are left
behind may build up to damaging levels. If the lady
beetles lay eggs before dispersing, the resulting
larvae continue to control aphids when the adults are
gone. Larvae provide better aphid control than adults
because they cannot fly away when aphid
populations are low.

Despite problems with dispersal, the convergent
lady beetle is widely advertised in gardening supply
catalogs for small-scale releases. Suppliers
recommend release rates ranging from 1 pint to 1
quart of beetles per home garden, and from 1 gallon
of beetles per acre to 1 gallon per 15 acres for field
scale releases. The basis for these release rates is
unclear.

Making releases at dusk (lady beetles do not fly
at night) and watering the release site so that plenty
of moisture is available may increase the chances
that the lady beetles will remain in the area. Some
distributors recommend spraying the beetles with a
dilute soft drink solution to glue their wing covers
down temporarily (to prevent flying), or providing


the beetles with artificial foods such as Bug Chow,
BugPro, or Wheast. Whether or not these
approaches help to keep lady beetles near the site of
release is not clear.

The Mealybug Destroyer, Cryptolaemus
montrouzieri

The mealybug destroyer (Figure 3) is an
Australian lady beetle. The adult is a small (about 4
mm), round, black beetle with an orange pronotum
and orange wing tips. The larva is covered with a
shaggy, white, waxy material, and resembles its
mealybug hosts when small. As its common name
implies, the mealybug destroyer feeds on all species
of above-ground mealybugs including the citrus
mealybug (Planococcus citri), which is a serious pest
of ornamental plants in greenhouses and interior
plantscapes. If mealybugs are not available, the
mealybug destroyer may feed on aphids and
immature scale insects. Both larvae and adults are
predaceous.








A B

Figure 3. The mealybug destroyer, Cryptolaemus
montrouzieri. A) Larva. B) Adult.

Adult mealybug destroyers lay several hundred
eggs, depositing them singly in mealybug egg
masses. Each beetle larva may consume more than
250 immature mealybugs in the course of its
development. The mealybug destroyer requires high
mealybug populations and optimum environmental
conditions in order to reproduce and is most effective
when used for quick reductions of heavy mealybug
infestations.

Development and reproduction of the mealybug
destroyer occur most rapidly at temperatures
between 22 and 250C (72 and 770F),and
relative humidities of 70-80%. Temperatures below
200C (680F) and short days slow the reproductive
rate of this predator but do not have as much effect






Beneficial Insects and Mites 7


on mealybug reproductive rates. As a result, the
mealybug destroyer is often unable to control
mealybug infestations during winter months in
greenhouses or other facilities where temperature and
day length are reduced.

Suppliers recommend releases of 1 beetle per 2
square feet of planted area or 2 to 5 beetles per
infested plant. Mealybug populations should not be
reduced insecticidally prior to beetle releases.
Although the mealybug destroyer is widely
advertised,supplies are often limited due to
difficulties in maintaining colonies.

The Green Lacewings, Chrysoperia
(formerly Chrysopa) carnea and
Chrysoperia rufilabris

Green lacewings (Figure 4) occur naturally
throughout North America and are widely available
for purchase and release. Adult green lacewings have
delicate, light green bodies, large, clear wings, and
bright golden or copper-colored eyes. The larvae are
small, greyish brown, and elongate and have
pincerlike mandibles. Green lacewing eggs are
found on plant stems and foliage. The are laid singly
or in small groups on top of fine, silken stalks which
reduce predation and parasitism by keeping the eggs
out of reach.


I -- B C
B

Figure 4. The common green lacewing, Chrysoperia
camea. A) Eggs. B) Larva, commonly known as an "aphid
lion." C) Adult.

Green lacewing larvae are generalist predators
of soft-bodied insects, mites, and insect eggs, but
they feed primarily on aphids and are commonly
known as "Aphid Lions." Lacewing larvae are also
cannibalistic, feeding readily on other lacewing eggs


and larvae if prey populations are low. Larvae feed
for about 3 weeks before pupating inside silken
cocoons that are usually attached to the undersides of
leaves.

Although adults of some lacewing species are
predaceous, Chrysoperia carnea adults feed only on
nectar, pollen, and aphid honeydew. Chrysoperia
carnea females cannot produce eggs if these foods
are not available. Green lacewing adults make long
dispersal flights soon after emerging from the pupal
stage; this dispersal takes place regardless of whether
or not ample food is present when the adults emerge.
Lacewings are night fliers and may travel many
miles before mating and starting to produce eggs.
Females are mobile throughout their egg-laying
period, although they concentrate where nectar and
honeydew are abundant. They tend to lay eggs
wherever they land to feed or rest.

Artificial foods, such as Bug Chow, BugPro
or Wheast, can be used in place of natural foods
(nectar and honeydew) to attract and concentrate
adult lacewings. The presence of artificial foods
does not keep newly emerged adults from dispersing,
but such foods may attract older adults that are in the
area. Food sprays are useful only when a substantial
population of lacewings is present in the area.

Lacewings are usually purchased as eggs. They
are shipped in a mixture of rice hulls and frozen
(killed) caterpillar eggs. The caterpillar eggs provide
food for the larvae that hatch during shipment, and
the rice hulls keep the larvae separated to minimize
cannibalism. Lacewings shipped in this manner are
meant to be released as soon as hatching begins.
Some insectaries offer lacewing eggs in sufficient
quantities for aerial application.

For small-scale gardens, suppliers recommend
release rates of 1 to 5 lacewing eggs per square foot
of garden space. For field crops recommendations
range from 50,000 to 200,000 lacewing eggs per
acre. Releases are made singly or sequentially at
2-week intervals, depending on the pest to be
controlled. In field trials for control of various
caterpillar and aphid pests in cotton, corn, and
apples, lacewing releases at these rates have provided
high levels of control and significant increases in
yields in some cases. However, the costs of






Beneficial Insects and Mites 8


purchasing and releasing such high numbers of
lacewing eggs may be prohibitive for commercial use.

Lacewing larvae are naturally tolerant of low
rates of several insecticides. Larvae are highly
susceptible to many other insecticides, however, and
adults tend to be more susceptible than larvae in all
cases.

Chrysoperia carnea, the common green
lacewing, is the most widely available lacewing
species. It is sold for general field and garden
releases. Chrysoperia rufilabris is an eastern
lacewing species that is better adapted for use in tree
crops. Chrysoperia rufilabris adults are predaceous
to a limited extent.

The Spined Soldier Bug, Podisus
maculiventris

The spined soldier bug (Figure 5) is the only
predaceous "true bug" (Order Hemiptera) available
for purchase. It occurs naturally in the United States
and is one of the most common predatory stink bugs.
The adult spined soldier bug is greyish brown with
sharply pointed corners on its pronotum. Nymphal
soldier bugs are various shades of orange with black
markings. They are round bodied and wingless.
Nymphs and adults stab their prey with long pointed
that are held folded under their bodies while not
feeding.


Figure 5. An adult spined soldier bug, Podisus
maculliventris, feeding on a Mexican bean beetle pupa.

Although the spined soldier bug is sold mainly
as a predator of Mexican bean beetle (Epilachna
varivestis) larvae, it is a generalist that feeds readily
on many soft bodies insects and larvae. Spined
soldier bug nymphs and adults feed on the same
kinds of prey, and if ample prey is available these


predators may provide some degree of control for
several weeks after the initial release (they are sold
as nymphs). At this time there are no adequate
guidelines for release rates.

Praying Mantids

Several mantid species occur naturally in the
southern U.S. In the fall, adult female mantids
produce egg cases that may contain up to two
hundred eggs. These eggs remain dormant until early
summer when tiny mantid nymphs hatch and begin
search for prey. Only one generation of mantids
develops each year.

Mantid nymphs and adults are indiscriminate
generalist predators that feed readily on a wide
variety of insects, including many beneficial insects
and other mantids. Older mantids feed on
medium-sized insects such as flies, honey bees,
crickets, and moths. They are not effective predators
on aphids, mites, or most caterpillars. Most of the
mantids that hatch from an egg case die as young
nymphs as a result of starvation, predation, or
cannibalism. In addition, mantids are territorial, and
by the end of the summer often only one adult is left
in the vicinity of the original egg case.

Although mantids are fascinating to watch in
action, they are nearly useless for pest control in
home gardens because of their indiscriminate
appetites and poor survival rate. Nevertheless, they
are widely advertised for sale to home gardeners.
Mantids are sold as egg cases, and the prices vary
greatly from one supplier to the next. The Chinese
praying mantid (Figure 6), Tenodera aridifolia
sinesis, is the species that is most commonly
available for purchase.


Figure 6. The Chinese praying mantid, Tenodera aridfollia
sinensis. A) Egg case with newly hatched nymphs. B)
Adult.






Beneficial Insects and Mites 9


The Predatory Mites, Phytoseiulus
persimilis and Other Species

Predators of twospotted spider mites. Mites in
the genera Phytoseiulus and Amblyseius are
fast-moving, pear-shaped predators with short life
cycles (from 7 to 17 days, depending on temperature
and humidity) and high reproductive capacities.
They are pale to reddish in color and can be
distinguished from two spotted spider mites by their
long legs, lack of spots, and rapid movement when
disturbed. The eggs of predatory mites are elliptical
and larger than the spherical eggs of spider mites.
Predatory mite nymphs feed on spider mite eggs,
larvae, and nymphs. Adult predators feed on all
developmental stages of spider mites.

Several species of predatory mites are sold by
U.S. distributors, but the only species that has been
studied extensively for use on a commercial scale is
Phytoseiulus persimilis (Figure 7). This mite
develops, reproduces, and preys on spider mites most
effectively in a temperature range of 210 to 270C
(70-80F), with relative humidities of 60-90%.
Above and below these ranges, Phytoseiulus
persimilis is less able to bring twospotted spider mite
populations under control.










A B

Figure 7. A) A predatory mite, Phytoseiulus persimilis,
adult and egg. B) The twospotted spider mite,
Tetranychus urticae, adult and egg.

Most of the scientific literature on the use of
Phytoseiulus persimilis in greenhouses deals with
commercial production of tomatoes and cucumbers
in Great Britain and the Netherlands. Evaluating
European research results and biological control
programs for use in U.S. greenhouses is difficult. In
the U.S., many greenhouses are used to produce
flowers or ornamental plants rather than vegetables.


The degree of spider mite control needed for
ornamentals is generally much higher than it is for
vegetables. In addition, production practices in U.S.
greenhouses differ from those in Europe.

In the U.S., insectaries generally recommend
releasing Phytoseiulus persimilis when there are 1 or
fewer spider mites per leaf throughout the
greenhouse. If spider mite populations exceed that
level, application of an insecticidal soap or other
nonresidual insecticide is recommended to reduce the
infestation before the predatory mites are releases.
Some insectaries recommend spot introductions to
control patchy spider mite infestations, while others
recommend systematic uniform introductions. The
best method depends on the distribution of the
twospotted spider mite. Release rate
recommendations range from 2 to 30 Phytoseiulus
persimilis per plant, depending on the stage and
susceptibility of the crop. Some experimentation
may be necessary to determine the appropriate
release rate and method for specific situations.

In Europe, twospotted spider mites are often
introduced intentionally to greenhouse crops at a low,
even rate soon after planting; this is followed some
days later by a uniform release of Phytoseiulus
persimilis. This "pest-in-first" method allow the
predatory mites to become established throughout the
greenhouse before natural spider mite outbreaks
occur in isolated spots. Another alternative is to
introduce spider mites and Phytoseiulus persimilis
simultaneously at the start of the growing season.
These techniques have been more consistently
successful than attempts to introduce the predatory
mite only after natural infestations have been
detected.

Phytoseiulus longipes and Amblyseius
californicus are sold in the U.S. for control of
twospotted spider mites. Phytoseiulus longipes, an
African species, tolerates temperatures up to 380C
(1000F) if humidity is high; it can tolerate low
relative humidities (down to 40%) at 21C (70'F).
Amblyseius californicus occurs naturally in
California, the Mediterranean, and several other
regions of the world. It is an important predator of
pest mites in California strawberry fields and is used
extensively for greenhouse releases. Amblyseiulus
californicus also tolerates higher temperatures (up to






Beneficial Insects and Mites 10


320C/900F). It consumes mites at a slower rate
than Phytoseiulus species, but is able to tolerate short
periods of starvation when spider mite densities are
low. Mixed releases of Phytoseiulus persimilis and
Amblyseius califomicus function well in greenhouses
where conditions and pest mite population densities
are variable.

Thrips predators. In addition to spider mite
predators, two species of predatory mites feed
primarily on thrips. Amblyseius cucumeris and
Amblyseius mckenziei (also known as Amblyseius
barker) feed on the western flower thrips
(Frankliniella occidentalis) and the onion thrips
(Thrips tabaci), both of which may be serious pests
in greenhouses. If introduced early in an infestation,
these mites can eliminate thrips populations in
greenhouses.

Amblyseius cucumeris and Amblyseius mckenziei
can subsist for short periods on pollen, fungi, or
spider mite ebbs when thrips are not available. These
mites require high relative humidities and are not
tolerant of insecticides. Short days inhibit egg
production by predatory mites, making thrips control
difficult during winter months.

U.S. suppliers recommend high release rates of
Amblyseius cucumeris and Amblyseius mckenziei for
control of thrips. For control of Thripstabaci on
sweet peppers, suppliers recommend releasing 10
predatory mites per plant plus an extra 25 mites per
infested leaf throughout the greenhouse. For
cucumbers, the recommended rate is 50 predatory
mites per plant plus an extra 100 per infested leaf.
For both crops, distributors recommend that
introductions be made weekly until there is 1
predatory mite for every 2 thrips. The efficacy of
these release rates is difficult to evaluate because
very little published research on Amblyseius
cucumeris or Amblyseius mckenziei exists. Literature
from Europe indicates that control may be possible
with lower release rates.


Parasitoids

Encarsia formosa,, A Parasitoid of the
Greenhouse Whitefly

Encarsiaformosa (Figure 8), a tiny parasitic
wasp, has been used to control greenhouse whiteflies
on tomatoes and cucumbers in Europe for over fifty
years. Encarsia adults lay their eggs into the
scalelike third and fourth nymphal stages of
whiteflies (see Figure 8). Parasitized whitefly
nymphs blacken and die as the parasitoid larva
develops inside. Adult wasps provide additional
whitefly control by feeding directly on early and late
nymphal stages.











Figure 8. An adult female Encarsia formosa depositing an
egg into the scalelike fourth nymphas stage of the
greenhouse whitefly.

Encarsia performs best when greenhouse
temperatures are maintained between 210 and
260C (700 and 800F), with relative humidities of
50-70%. In these conditions, Encarsia reproduces
much faster than the whitefly. At lower temperatures
the whitefly reproduces more rapidly than the
parasitoid, and Encarsia may not provide adequate
control. In addition, Encarsia requires bright light
for optimum reproduction and development. This
dependence on light intensity further limits the
parasitoid's effectiveness during winter months when
day length is shorter and light intensities are lower.

Numerous release schedules have been
developed for Encarsia. As with predatory mites,
most or the research and practical information on
Encarsia has come form Great Britain and the
Netherlands and involves commercial tomato and
cucumber production. In these countries the
"pest-in-first" method (introducing the pest at low
levels before releasing the natural enemy) is
commonly used for whitefly control. Where this






Beneficial Insects and Mites 11


approach is not used, Encarsia must be released at
the very first sign of whitefly infestation. As with
releases of predatory mites for spider mite control
provided by Encarsia is not likely to by sufficient for
production of commercial ornamentals.

Most U.S. Encarsia suppliers recommend that
releases be made when there is an average of less
than 1 adult whitefly per upper leaf (regardless of
plant species) on all plants throughout the
greenhouse. Introductions should be made
sequentially (usually at 2-week intervals) for several
weeks in order to control immature whiteflies as they
hatch. Release rate range from 1 to 5 wasps per
square foot or from 1 to 8 per plant, depending on
plant species and the severity of the infestation.
Evidence of parasitism by Encarsia (presence of
blackened whitefly scales) becomes apparent 2 to 3
weeks after the initial release, and whitefly
populations are usually reduced to low levels within
2 to 3 months. After Encarsia has become
established in a greenhouse, it continues to reproduce
and control whitefly populations as long as
conditions are favorable and the whitefly is present.

Trichogramma Wasps, Egg Parasitoids

The Trichogramma wasps (Figure 9) are the
most commonly used parasitoids worldwide. They
are released extensively in Europe and Asia for the
control of many species of caterpillar pests in various
crops. Trichogramma wasps are extremely small,
averaging about 0.7 mm in length as adults (the size
of the period at the end of this sentence).


Figure 9. Adult Trichogramma wasp.

Most Trichogramma species lay their eggs into
the eggs of moths and butterflies. A few species


parasitize eggs of other kinds of insects.
Trichogramma larvae develop within host eggs,
killing the host embryos in the process. Instead of a
caterpillar hatching from a parasitized egg, one or
more adult Trichogramma wasps emerge. Because
the caterpillar pests are killed in the egg stage, no
feeding damage occurs. This makes Trichogramma
an especially important natural enemy for control of
pests such as codling moth larvae, European corn
borers, and corn earworms, all of which bore into
plant tissues and cause economic damage soon after
hatching.

There are many species of Trichogramma, and
each prefers different hosts. Although several
Trichogramma species are generalist parasitoids,
many parasitize only one or a few related species.
Three species are commonly available for purchase
and release in the U.S. Trichogramma presotiosum,
sold for control of caterpillar pests in field crops,
vegetables, and stored grain, is capable of
parasitizing over 200 species of caterpillar eggs
(although it is not equally effective against all of
those species). Trichogramma minutum is sold for
control of forest caterpillars. The third species,
Trichogramma platerni, parasitizes a caterpillar pest
of avocadoes and is not. Trichogramma nubilale, a
species currently under research, shows promise as
an effective parasitoid of the European corn borer; it
is not yet available for purchase.

Success with Trichogramma is extremely
variable. In research trials, it has been used in single
or sequential releases at rates of 50,000-300,000
wasps per acre per release. Trichogramma wasps are
usually released as mature pupae inside host eggs.
Adult wasps emerge within 1 to 3 days of release and
are active for about 9 days. If a mixture of larval
-stage and pupal-stage parasitoids is released,
activity is extended by several days. Releases are
usually timed to correspond with the start of egg
laying by the pest, as determined by pheromone
trapping or other monitoring methods.

The size and host-finding ability of
Trichogramma wasps are partially dependent on the
species of host egg within which the wasps are
reared. Most insectaries rear Trichogramma in the
eggs of the Angoumois grain moth, Sitotroga
cerealella, because this moth is easy to rear






Beneficial Insects and Mites 1


inexpensively in large numbers. Angoumois grain
moth eggs are very small, however, and the resulting
parasitoids may also be small and not well suited to
locating and parasitizing eggs of other target pest
species when released in the field. Locally collected
species or strain of Trichogramma reared on the
intended target host are more likely to be successful
for field releases than exotic species; however,
rearing facilities do not provide customized regional
production.

Filth Fly Parasitoids, Muscidifurax and
Spalangia Species

Most parasitoids sold for use in the biological
control of filth flies around livestock and poultry are
wasps in the genera Muscidifurax and Spalangia.
Adult wasps in these genera are less than 2.5 mm
long. They deposit their eggs in or on fly pupae
located in manure or other breeding sites. These
wasps parasitize both house fly and stable fly pupae
located in manure or other breeding sites. These
wasps parasitize both house fly and stable fly pupae,
but different species exhibit different host or habitat
preferences.

Studies of the effectiveness of releasing
parasitoids for fly control have produced mixed
results, and the use of parasitoids for the control of
filth flies must be considered somewhat
experimental. Nonetheless, several key findings can
serve as guidelines for release programs.

The parasitoid species most likely to contribute
to the control of house flies in cattle feedlots are
Muscidifurax raptor and Muscidifurax zaraptor. For
the control of stable flies in feedlots, Spalangia
nigroanea and Spalangia cameroni are most likely to
provide benefits. (These two Spalangia species also
parasitize house flies, but not as frequently as the
Muscidifurax species.) Two commonly sold
parasitoids are very unlikely to provide any benefit
in feedlots; neither Nasonia vitripennis nor Spalangia
endius parasitized a significant percentage of house
flies or stable flies when released in large numbers in
studies conducted in Midwest (Kansas and
Nebraska) feedlots. Because these two parasitoids
are distributed by several companies but are unlikely
to provide any significant fly control in feedlots,
cattle producers are cautioned not to purchase


"generic" fly parasitoids that are not identified by
species.

Available data indicate that release rates
recommended by suppliers of fly parasitoids are
probably too low to provide much fly control in
feedlots. Although suppliers often recommend
weekly releases of 5 to 20 parasitoids per animal,
significant control of stable flies requires releases of
50 to 100 Spalangia nigroaenea or Spalangia
cameroni per animal per week. Simultaneous weekly
releases of 50 to 100 Muscidifurax raptor or
Muscidifurax zaraptor per animal are necessary for
house fly control. Although these release rates
exceed the recommendations of most suppliers, they
still can be economically feasible.

Parasitoids can be used effectively for house fly
control in poultry facilities, especially those with
concrete floors. Muscidifurax raptor, Muscidifurax
zaraptor, Spalangia cameroni, Spalangia nigroaenea,
and Spalangia endius parasitize house fly pupae in
poultry buildings. Pachycrepoideus vindemiae, also
shown to be useful in poultry buildings, is available
from some insectaries. Release rates for the use of
these parasitoids in poultry depend upon house
construction and manure management, but a general
recommendation is the weekly release of 1 parasitoid
per 2 bird. Practices that minimize moisture
problems (fixing leaks and improving drainage) help
to lower the moisture content of manure
accumulations and contribute to parasitoid buildup
and fly control. Removing only a portion of the
manure (for example, under alternate rows of cages)
at any one time also favors parasitoid success.

Some Common Naturally Occuring
Beneficial Insects And Mites

Few guidelines exist for monitoring populations
of natural enemies and determining their likely
impacts on pest infestations. Nonetheless,
recognizing the beneficial that are present in any
situation and understanding their roles are useful
steps in deciding on appropriate pest management
practices. Some common, naturally occurring
species include:




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