Beneficial Insects

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Beneficial InsectsBeneficial insects have many roles in the environment, including in agricultural systems. Those we are most familiar with are pollinators, nutrient cyclers and natural enemies. Natural enemies play an important role in suppressing populations of many of the key pest species common in grain crops.

Being aware of, and familiar with, the suite of natural enemies that are active in your crops is the first step in recognising them as an integral part of the crop fauna. The preservation of natural enemies, through the judicious and selective use of insecticides, is central to harnessing the contribution that these important insects make to suppressing pest populations, and consequently minimising crop loss.

This guide provides a snapshot of key natural enemies of pests commonly encountered in grain crops in the northern region. The photographs and information on identification are designed to assist growers to include natural enemies in their day to day crop monitoring.

Caterpillar parasitoids – waspsDescriptionSeveral small to medium-sized (3 to 20mm) wasps contribute to the biocontrol of pest larvae, including armyworm and Helicoverpa. Caterpillar parasitoids tend to be slender, the most common species are black, orange or black, orange and white.

Detecting them in the fieldAdult wasps are commonly observed flying in crops, or attracted

to lights at night. The black eggs of Netelia wasps are visible attached to the head of parasitised larva.

Impact on pestMost species attack larvae, but do not kill the larva until it pupates. Microplitis – another wasp species – do kill mid-sized larvae, and their cocoons adhere to larvae. Some Microplitis transmit ascovirus which

kills the caterpillar.

Netelia adult Microplitis cocoon and larvaPHoTo: J HoPkiNSoN – DEEDi PHoTo: N PArkEr – DEEDi

Caterpillar parasitoids – fliesDescriptionTachinid flies are stout-bodied and bristly and usually grey-brown in colour. They range in size from 5 to 10mm in length. There are many species of tachinids parasitising caterpillars, bugs and beetles.

Detecting them in the fieldTachinid activity is most evident from the presence of white eggs

adhering to the head and ‘neck’ of caterpillars.

Impact on pestTachinid larvae develop in the host, but do not kill them until they pupate. They play a role in reducing pest populations over time. in grain crops, noctuid caterpillars (armyworm, Helicoverpa, loopers) are commonly attacked.

Tachinid adultPHoTo: J WESSElS – DEEDi

Noctuid larva with tachinid egg attachedPHoTo: J WESSElS – DEEDi

Bug parasitoids – fliesDescriptionThe green vegetable bug parasitoid (Trichopoda giacomellii) has been introduced to some areas of the northern region. Adult flies are about 8mm long, female flies are black, males orange.

Detecting them in the fieldoff-white eggs adhering to adult and final nymph instar are the most obvious sign of Trichopoda activity.

Impact on pestParasitised bugs stop feeding soon after being attacked,

but do not die for up to two weeks.

Green vegetable bug with Trichopoda eggs adhering to thorax PHoTo: J WESSElS – DEEDi

Trichopoda femalePHoTo: J WESSElS – DEEDi

Helicoverpa egg parasitoidsDescriptionTrichogramma and Telenomus egg parasitoids are tiny wasps that lay their eggs into caterpillar eggs, killing the developing larvae. Trichogramma are yellow-brown with red eyes, Telenomus is black with black eyes. Egg parasitoids are about 0.5mm in length.

Detecting them in the fieldSeeing these tiny wasps and the black, parasitised eggs in the

field is difficult. To determine if they are active, collect the eggs of the caterpillar pest and store them for 10 days. if

parasitised, the eggs will turn black and an adult wasp will emerge. if unparasitised, a caterpillar larva will emerge.

Impact on pestEgg parasitoids can limit crop damage as they kill the

caterpillar before it emerges from the egg. They attack all major caterpillar pests of grain crops.

Trichogramma adult inspecting eggPHoTo: B SCHolz – DEEDi

Unparasitised white egg, left, and parasitised black eggPHoTo: B SCHolz – DEEDi

Whitefly parasitoidsDescriptionEretmocerus sp. and Encarsia sp. are small (0.5mm) parasitoid wasps that attack whitefly nymphs. These wasps are active throughout the year in crops and non-crop vegetation that host whitefly.

Detecting them in the fieldNymphs parasitised by Encarsia turn black, and this change is

visible in the field with a hand lens. Parasitism by Eretmocerus is more difficult to determine as there is no obvious colour

change.

Impact on pestParasitised nymphs do not emerge as adult whitefly, so the activity of these parasitoids which attack whitefly nymphs can have a significant impact on the

rate of population build-up in the crop.

Encarsia adult PHoTo: z luDgATE – DEEDi

Parasitised whitefly nymphs (blackened)PHoTo: z luDgATE – DEEDi

Predatory bugsDescriptionSmall to medium predatory bugs are common in grain crops. The damsel bug, Nabis kingbergii, is 8mm in length, pale-coloured and slender, with long antennae. Nymphs are similar in appearance to adults but lack wings.

Detecting them in the fieldPredatory bugs are active in the canopy. These small, slender

bugs are often overlooked in scouting, but are readily dislodged with beatsheet sampling.

Impact on pestThese bugs attack a wide range of soft-bodied prey including aphids, whitefly nymphs, small caterpillars, leafhoppers, mites, immature bugs and beetles.

Damsel bug adultPHoTo: k PoWEr – DEEDi

Damsel bug nymphPHoTo: J WESSElS – DEEDi

Predatory bugsDescriptionSmall to medium predatory bugs are common in grain crops. The adult brown smudge bug, Deraeocoris signatus, is small (4.5mm) and mottled brown. Nymphs are maroon, and often mistaken for aphids.

Detecting them in the fieldPredatory bugs are active in the canopy. These small, slender

bugs are often overlooked in scouting, but are readily dislodged with beatsheet sampling.

Impact on pestThese bugs attack a wide range of soft-bodied prey including aphids, whitefly nymphs, small caterpillars, leafhoppers, mites, immature bugs and beetles.

Brown smudge bug adultPHoTo: J WESSElS – DEEDi

Brown smudge bug nymphPHoTo: J WESSElS – DEEDi

Bug egg parasitoidDescriptionTrissolcus basalis are small, shiny black wasps (0.5mm). Trissolcus does not distinguish between the eggs of pests and beneficial species, and will parasitise eggs of the predatory shield bugs as well as the green vegetable bug.

Detecting them in the fieldParasitised eggs turn black as the wasp larva develops inside them. Parasitised eggs of the green vegetable bug (gVB) can be distinguished from the naturally dark eggs of the predatory shield bugs, which have a fringe of spines around the top.

Impact on pestParasitised eggs are killed as the wasp larva develops inside them, and an adult wasp – rather than a bug nymph – emerges.

Trissolcus adult on GVB egg massPHoTo: H BriEr – DEEDi

Predatory beetlesDescriptionlabybirds are probably the most recognisable beneficial insect in grain crops. There are a number of species, most are brightly coloured yellow or red with black and white spots or lines. Adults are shiny, round to oval (3 to 7mm). larvae tend to be grey-black and elongated with yellow markings. Eggs are bright yellow, elongated and laid in clusters.

Detecting them in the fieldThe bright colours of adults make them highly visible in the

crop. larvae can be more difficult to observe, but easily seen in colonies of aphids, mites and other pests.

Impact on pestBoth larvae and adults are predacious. Across the species, ladybirds have a wide range of prey including

aphids, mites, whitefly, thrip, small caterpillars, moth eggs and scale.

Transverse ladybird adults and larvaPHoTo: D iroNSiDE – DEEDi

Ladybird eggsPHoTo: J WESSElS – DEEDi

Predatory shield bugDescriptionThe spined predatory bug, oechalia schellenbergii, has distinctive spines on its shoulders. These bugs are large (11mm), and prey on caterpillars, bug pests and other soft-bodied insects. Nymphs do not have spines, but have a distinctive red-orange ring on their backs.

Detecting them in the fieldAdult bugs are often seen in the field and can be easily

dislodged when sampling with a beatsheet. Eggs are laid in rafts and are distinctive with their fringe of long spines around the top. Early instar nymphs tend to aggregate.

Impact on pestAdults and nymphs are predatory, feeding on and killing

a wide range of soft-bodied prey. These large bugs are capable of killing medium-to-large caterpillar larvae.

Oechalia adult feeding on GVB nymphPHoTo: k kNigHT – DEEDi

Oechalia eggsPHoTo: J. WESSElS – DEEDi

Predatory shield bugDescriptionThe glossy shield bug, Cermatulus nasalis, is a large (12mm) predatory shield bug. These bugs prey on caterpillars, bug nymphs and other soft-bodied insects. Nymphs are dark with four red-orange spots on their back.

Detecting them in the fieldAdult bugs are often seen in the field and can be easily dislodged

when sampling with a beatsheet. Eggs are laid in rafts and are distinctive with their fringe of long spines around the top.

Early instar nymphs tend to aggregate.

Impact on pestAdults and nymphs are predatory, feeding on and killing a wide range of soft-bodied prey. These large bugs are capable of killing medium-to-large caterpillar

larvae.

Glossy shield bug adultPHoTo: J WESSElS – DEEDi

Glossy shield bug nymphPHoTo: H BriEr

LacewingsDescriptionAdult lacewings hold their tent-like, clear wings over their back, have long antennae and prominent eyes. The brown lacewing (8mm) is mottled brown and the green lacewing is larger (15mm) and pale to bright green. larvae have forward-protruding, sickle-shaped jaws. green lacewing larvae are stout and camouflage themselves with the bodies of their prey. Brown lacewing larvae are elongated, and do not camouflage themselves.

Detecting them in the fieldClusters of green lacewing eggs are distinctive due to their long

stalks, and indicate lacewing activity.

Impact on pestAdults of the green lacewing are not predatory. Brown adults and larvae of both species feed on soft-bodied insects, mites and eggs.

Brown lacewing adultPHoTo: J WESSElS – DEEDi

Green lacewing eggs (left) and green lacewing larva (right)PHoToS: J WESSElS – DEEDi

HoverflyDescriptionAdult hoverflies are small (4 to 7mm), slender flies with dark and yellow markings on the body. They are often mistaken for wasps. Characteristically, adults hover in the crop. Small, white, oval eggs are laid close to aphid colonies. larvae are green (up to 8mm) and maggot-like.

Detecting them in the fieldAdults are easily observed flying and hovering in the crop. To

find larvae, look carefully in colonies of aphids, although they can be difficult to see without close inspection. Tear-shaped pupae may be found adhering to leaves.

Impact on pestAdults are not predatory. larvae are voracious predators and kill aphids by piercing them and

sucking them dry.

Hoverfly adultPHoTo: J WESSElS – DEEDi

Hoverfly larvaPHoTo: J WESSElS – DEEDi

SpidersDescriptionA large variety of spiders occur in grain crops, including active hunters like the wolf, lynx and nightstalkers, or web spinners like the tangle web and orbweaver. While considered relatively sedentary, juvenile spiders can travel large distances on the wind and colonise fields.

Detecting them in the fieldMost spiders are well-camouflaged, and many are active at night either hiding in nests in the soil or in the canopy. Spiders are often dislodged onto beatsheets when sampling.

Impact on pestSpiders have a broad range of prey. Active hunters prey on slow-moving targets including caterpillars, bug nymphs and eggs. Webspinners can catch flying prey.

Jumping spiderPHoTo: J WESSElS – DEEDi

Aphid parasitoidsDescriptionSeveral species of wasp parasitise aphids and it is difficult to distinguish between the species in the field. generally they are small (2 to 3mm) and dark with clear wings and long antennae.

Detecting them in the fieldAdult wasps can be difficult to see because of their small size. The presence of parasitised aphid ‘mummies’ is evidence of

parasitoid activity. When fully developed the wasps emerge from a circular hole in the ‘mummy’.

Impact on pestFemale wasps insert eggs into live aphids, and the wasp larva grows within the aphid. Aphid parasitoids can have a major impact on aphid populations.

Adult parasitoidPHoTo: M MilES – DEEDi

Aphid mummy showing wasp emergence holePHoTo: M MilES – DEEDi

Disclaimer: Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Grains Research and Development Corporation (GRDC) and Agri-Science Queensland, Department of Employment, Economic Development and Innovation (DEEDI). No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. The GRDC and Agri-Science Queensland, DEEDI will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.

Copyright: © All material published in The Back Pocket Guide is copyright protected and may not be reproduced in any form without written permission from the Grains Research and Development Corporation and Agri-Science Queensland, DEEDI.

September 2010

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useful resources

GrdC Pest Links www.grdc.com.au/pestlinks

GrdC Integrated Pest Management Fact Sheet www.grdc.com.au/factsheets

deedI Insect Pest management website www.dpi.qld.gov.au/26_3510.htm

the Beatsheet Blog www.thebeatsheet.com.au

Crop Insects: The Ute Guide (Northern Region Grain Belt edition), copies available at Ground Cover direct