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GUIDE TO INSECT FAMILIES WITH PREDATORY & PARASITIC SPECIES

INTRODUCTION

Most insect species rarely reach outbreaking numbers that result in severe defoliation and death of the host plant nor do they often display a numerical abundance which is intolerable to humans. This is generally true in natural, relatively undisturbed environments. However, in the highly artificial environments associated with human habitation, population upsets sometimes result from insecticidal applications; other times from the lack of suitable natural enemies or disturbances to their maximum performance.

It may seem almost an oversimplification to suggest that the relative stability of populations of potential pest insects is due solely to the activity of effective natural enemies (= density dependence). However, evidence from four main sources suggests just that. In the first case, the many successful examples of biological control of pest insects by importation and release of natural enemies supports the density dependent hypothesis. Secondly, pest outbreaks can be produced when natural enemies are excluded by pesticides or other experimental means. Thirdly, ecologists have strong evidence from long term determinations of the complex interrelationships of insect populations. Finally, there are the often overlooked accidental cases of detrimental biological control, which support the density dependent hypothesis, such as Dutch elm disease, Chestnut blight, the decline of Bermuda cedars; and of course all cases of invaded pests that cause a drop in the average abundance of a plant or animal population.

Kinds & Numbers of Insect Natural Enemies

There are many different kinds of predatory and parasitic insects; certainly more than is generally appreciated by the public. Many of the less conspicuous types exert a far greater impact on the prey they attack than the larger more bizarre forms, such as the preying mantids, lacewings and ladybird beetles. Their common names do not always indicate their predatory or parasitic nature. The following list of principal groups is accompanied by a brief notation on habits of predaceous or parasitic species, and estimated numbers as of 1995. A more detailed treatment is given to the most important groups of parasitic wasps, the Hymenoptera. Natural enemy families and subfamilies, and some nonpredacious and nonparasitic groups for distinction, are included:

ANOPLURA ("sucking lice," ca. 612 species, blood-sucking only)

COLEOPTERA ("beetles," 332,000 species)

Anthicidae ("antlike flower beetles," insect predators)

Anthribidae ("fungus weevils," scale insect predators)

Cantharidae ("soldier beetles," aphid, grasshopper egg and larval Coleoptera & Lepidoptera predators)

Carabidae ("ground beetles," 25,100 species of general predators)

Cicindelidae ("tiger beetles," 2,020 species of general predators)

Cleridae ("checkered beetles,", 3,420 species predators of wood-boring insects)

Coccinellidae ("ladybird beetles," 3,320 species primarily insect predators)

Colydiidae ("cylindrical bark beetles," several species predators of wood-boring beetles)

Cucujidae (incl. Passandridae) ("flat bark beetles," many species predators of wood-inhabiting beetles and

some termites)

Dascillidae ("soft-bodied plant beetles)

Dermestidae ("skin beetles," a few general predators)

Drilidae ("drilid beetles," snail predators)

Dytiscidae ("predaceous diving beetles," 4,030 species aquatic predators)

Ectrephidae ("ectrephid beetles")

Elateridae ("click beetles," some species soil insect predators)

Gyrinidae ("whirligig beetles," 260 species predators in aquatic environments)

Haliplidae (crawling water beetles")

Helodidae ("marsh beetles," a few species of aquatic predators)

Histeridae ("hister beetles," 3,520 species predators of carrion- or excrement-feeding insects, wood-borers,

etc.)

Hydrophilidae ("water scavenger beetles," predators as larvae in aquatic environments)

Hygrobiidae ("hygrobid beetles," pond inhabiting predators)

Lampyridae ("fireflies," predators of snails and other soil organisms).

Lathridiidae ("minute brown scavenger beetles," predators of scale insects)

Leptinidae ("mammal nest beetles," a few species parasites of ants)

Lycidae ("net-winged beetles")

Meloidae ("blister beetles," 2,040 species predator/parasites of wild bees and grasshoppers)

Melyridae (= Malachiidae) ("soft-wing flower beetles," 4,010 species general predators)

Mordellidae ("tumbling flower beetles," predators of larvae of stem- & wood-boring insects)

Mycetophagidae ("fungus gnats," predators of adult mosquitoes & scale insects)

Nitidulidae ("sap beetles," some predators of scale insects)

Ostomatidae ("bark gnawing beetles," a few predators of wood-inhabiting beetles)

Paussidae ("ground beetles," a few may be predators of ants)

Phalacridae ("shining flower beetles," some predators of aphids)

Phengodidae ("glow worms," rarely predators of myriapods)

Pselaphidae ("short-winged mold beetles," a few may be predators of ants)

Pythidae (= Salpigidae) ("narrow-waisted bark beetles," a few predators of bark beetles)

Rhipiceridae ("cedar beetles," one species parasitic on cicadas)

Rhipiphoridae ("wedge-shaped beetles," 240 species parasitic on Hymenoptera & some cockroaches)

Rhizophagidae ("root-eating beetles," predators of bark beetles & Phoridae)

Scarabaeidae ("scarab beetles," some predators of locust eggs and horn flies)

Silphidae ("carrion beetles," predators of ants, snails & flies)

Staphylinidae ("rove beetles," 30,100 species, general predators and some parasites)

Tenebrionidae ("darkling beetles," possibly some predators of bark & wood-boring insects)

Trogidae ("trogid scarab beetles")

Trogossitidae (= Ostomidae) ("bark-gnawing beetles")

COLLEMBOLA ("springtails," 2,400 species, scavengers or plant-feeding)

DERMAPTERA ("earwigs," 1,412 species, general predators)

DIPLURA ("diplurans," 890 species, scavengers)

DIPTERA (true flies, >160,000 species)

Orthorrhapha

Asilidae ("robber flies," general predators)

Bombyliidae ("bee flies," predators of bees & wasps)

Cecidomyiidae ("gall gnats," a few predators of aphids & scale insects)

Ceratopogonidae ("biting midges," ectoparasites & predators of other insects)

Chironomidae ("aquatic midges," predators of other aquatic midges)

Culicidae ("mosquitoes," some predators of other mosquitoes)

Dolichopodidae ("long-legged flies," some are predators of other insects)

Empididae ("dance flies," predators of other insects)

Mycetophilidae ("fungus gnats," some predators of other insects)

Mydidae ("mydas flies," larvae & adults are predators of other insects)

Nemestrinidae ("tangle-veined flies," 2 species predators of grasshoppers)

Rhagionidae (Leptidae) ("snipe flies," adults & larvae are predators of small insects)

Scenopinidae ("window flies," some larvae are predators of carpet beetles)

Stratiomyiidae ("soldier flies," some predators of small aquatic animals)

Tabanidae ("horse & deer flies," most larvae are predators of other aquatic animals)

Therevidae ("stiletto flies," larvae are predators of other insects in sand or decaying wood)

Tipulidae ("crane flies," a few larvae are predators of other insects)

Cyclorrhapha

Acroceridae ("small-headed flies," larvae are internal parasites of spiders)

Agromyzidae ("leafminer flies," one genus parasitic on scale insects)

Anthomyiidae ("anthomyiid flies," some larvae aquatic predators)

Apioceridae ("flower-loving flies," some predators of other insects)

Braulidae ("bee lice," commensals on bees)

Calliphoridae ("blow flies," some predators of other insects (ants, termites, etc.)

Chamaemyidae (Ochthiphilidae) ("aphid flies," predators of aphids)

Chloropidae (Oscinidae) ("chloropid gnats," a few predators and parasites of insects)

Conopidae ("thick-headed flies," larvae are endoparasites of bees & wasps)

Drosophilidae ("pomace or small fruit flies," a few ectoparasites of caterpillars & predators of Homoptera)

Lonchaeidae ("lonchaeid flies," larvae are predators of beetles)

Milichiidae ("milichiid flies," some commensals of predaceous insects; adults are predators)

Otitidae (Ortalidae) ("picture-winged flies," a few predators of locust eggs)

Phoridae ("humpbacked flies," some internal parasites of other insects (ants, termites)

Pipunculidae ("big-headed flies," larvae are parasites of leafhoppers & planthoppers)

Pyrgotidae ("pyrgotid flies," larvae are predators of June beetles)

Sarcophagidae ("flesh flies," some parasites of other insects (bees & wasps)

Scatophagidae (Cordyluridae) ("minute black scavenger flies," adults are predators of small flies; some may be

parasites of caterpillars)

Syrphidae ("flower flies," predators of aphids & other Homoptera)

Tachinidae ("tachinid flies," parasites of other insects)

EMBIOPTERA ("webspinners," 240 species, plant-feeding)

EPHEMEROPTERA ("mayflies," 3,240 species, plant-feeding)

HEMIPTERA / HETEROPTERA (true bugs, 46,412 species)

Anthocoridae ("minute pirate bugs," general insect predators)

Belostomatidae ("giant waterbugs," general predators)

Coreidae ("leaf-footed bugs," a few are predators of other insects)

Corixidae ("water boatmen," a few predators of other insects)

Enicocephalidae ("gnat bugs," predators of small insects)

Gelastocoridae ("toad bugs," general predators)

Gerridae ("water striders," general insect predators)

Lygaeidae ("seed & big-eyed bugs," some predators of other insects)

Mesoveliidae ("water treaders," predators of small aquatic organisms)

Miridae ("plant & leaf bugs," a few predators of other insects)

Nabidae ("damsel bugs," general predators)

Naucoridae ("creeping water bugs," predators of small animals)

Nepidae ("water scorpions," general predators)

Notonectidae ("backswimmers," general predators)

Ochteridae ("velvety shore bugs," general predators)

Pentatomidae ("stink bugs," predators of Lepidoptera)

Phymatidae ("ambush bugs," general predators)

Reduviidae ("assassin bugs," general predators)

Saldidae ("shore bugs," general predators)

Vellidae ("broad-shouldered water striders," general predators)

HOMOPTERA ("cicadas, leafhoppers, aphids, psyllids & whiteflies," 39,400 species, plant-feeding)

HYMENOPTERA ("bees, wasps, ants," >187,000 species)

Symphyta (Chalastogastra)--sawflies & horntails

(Sawflies, mostly plant-feeding)

Orussoidea

Orussidae ("parasitic wood wasps," 2 species internal parasites of beetles)

Tenthredinoidea

Tenthredinidae ("common sawflies," several species predators of other insects)

Apocrita (Clistogastra, Petiolata)-- parasitic/predatory

Apocrita Aculeata (stinging Hymenoptera)

Apoidea

Andrenidae ("mining bees," 2,300 species)

Anthophoridae ("carpenter, cockoo & digger bees," 6,225 species)

Apidae ("honey & euglossine bees," 1,082 species, but only a few bumblebee predators)

Colletidae ("plasterer & yellow-faced bees," 2,105 species, predators of other bees)

Halictidae ("halictid bees," 3,520 species, predators of other bees)

Megachilidae ("leaf-cutting bees," 6,400 species, predators of other bees)

Melittidae ("melittid bees," 135 species)

Bethyloidea (= Chrysidoidea)

Bethylidae ("bethylid wasps," 2,224 species, many parasitic on Lepidoptera)

Chrysididae (+ Cleptidae) ("cuckoo wasps," 3,100 species parasitic on bees & wasps)

Dryinidae ("dryinid wasps," 1,094 species parasitic on Homoptera)

Embolemidae ("embolemid wasps," 14 species parasitic on leafhoppers)

Sclerogibbidae ("sclerogibbid wasps," 12 species)

Formicoidea

Formicidae ("ants," 8,763 species of general predators)

Pompiloidea

Rhopalosomidae ("rhopalosomatid wasps," 37 species, a few cricket parasites)

Pompilidae (= Psammocharidae) ("spider wasps," 4,232 species parasitic on spiders)

Scolioidea

Scoliidae ("digger wasps," 312 species parasitic on scarab & curculionid beetles)

Sphecoidea

Sphecidae ("sphecid wasps," 7,322 species parasitic on insects & spiders)

(Ampulicinae)-- (172 species, cockroach parasites)

(Bembicinae)-- (572 species, predators of syrphid and tabanid flies)

(Cercerinae)-- (896 species, predators of bees & beetles)

(Crabroninae)-- (1,310 species, general predators)

(Larrinae)-- (1,787 species, some true parasites of mole crickets)

(Mellininae)-- (13 species fly predators)

(Nyssoninae)-- (221 species, predators of Homoptera)

(Pemphredoninae)-- (503 species, predators of aphids)

(Philanthinae)-- (152 species, predators of bees)

(Pseninae)-- (92 species, predators of Homoptera)

(Sphecinae)-- ("mud dauber & thread-waisted wasps," 665 species, general predators)

(Stizinae)-- (310 species, predators of Homoptera & Orthoptera)

(Trypoxyloninae)-- (742 species, predators of spiders)

Tiphioidea

Mutillidae ("velvet ants," 5,110 species, parasites of other Hymenoptera)

Sapygidae ("sapygid wasps," 83 species, a few parasites of bees)

Thynnidae ("thynnid wasps," 1010 species, several parasitic on scarab beetles)

Tiphiidae ("tiphiid wasps," 500 species, parasitic on beetle larvae)

Vespoidea

Eumenidae ("mason, potter & mud wasps," 3,025 species)

Methocidae ("methocid wasps," ectoparasites of soil beetles)

Vespidae ("paper wasps, hornets, yellow jackets," 1,028 species predatory on many insects)

Apocrita Parasitica (nonstinging Hymenoptera)

Ceraphronoidea

Ceraphronidae ("ceraphronid wasps," 620 species parasites or hyperparasites of braconid & chalcid wasps)

Megaspilidae ("megaspilid wasps," 453 species)

Chalcidoidea

Agaonidae ("fig wasps," probably >400 species, pollinators of figs)

Aphelinidae ("aphelinid wasps," 1,128 species parasitic on Homoptera)

Chalcididae ("chalcidid wasps," 1,833 species generally parasitic)

(Chalcidinae, Cleonyminae, Dirhininae, Epitraninae, Haltichellinae, Smicromorphinae)

Elasmidae ("elasmid wasps," 263 species, several parasitic or hyperparasitic on Lepidoptera)

Encyrtidae ("encyrtid wasps," 3,831 species parasitic on Homoptera)

Eucharitidae (= Eucharidae) ("eucharitid wasps," 391 species parasitic on ants)

(Eucharitinae, Oraseminae)

Eulophidae ("eulophid wasps," 3,820 species parasitic on Lepidoptera & other insects)

(Entedoninae, Euderinae, Eulophinae, Tetrastichinae)

Eupelmidae ("eupelmid wasps," 898 species parasitic on Hymenoptera & Diptera)

Calosotinae, Eupelminae, Metapelmatinae)

Eurytomidae ("eurytomid wasps," 1,432 species parasitic on Diptera, Coleoptera & Hymenoptera in galleries)

(Eurytominae, Heimbrinae, Rileyinae)

Leucospidae ("leucospid wasps," 251 species, several parasitic on bee larvae)

Mymaridae ("fairy flies," 1,395 species parasitic on Homoptera eggs)

Mymerommatidae (= Callimomidae) ("mymerommatid wasps," 9 species)

Ormyridae ("ormyrid wasps," 92 species, several parasitic on Hymenoptera)

Perilampidae (perilampid wasps," 271 species hyperparasitic on Lepidoptera)

(Chrysolampinae, Perilampinae)

Pteromalidae ("pteromalid wasps," 3,800 species parasitic on Lepidoptera, Coleoptera & Diptera)

(Asaphinae)-- (parasites of hyperparasites of Homoptera & Neuroptera)

(Austroterobiinae)-- (parasites of scale insects)

(Brachyscelidiphaginae)-- (plant gall-forming)

(Ceinae)-- (parasites of leaf-mining Diptera)

(Cerocephalinae)-- (parasites of small wood-boring beetles)

(Chalcedectinae)-- (parasites of wood-boring beetles)

(Chromeurytominae)-- (rare & habits unknown)

(Chrysolampinae)-- (parasites of beetles)

(Cleonyminae)-- (a few species parasitic on chrysomelid beetles)

(Coelocybinae)-- (plant gall-forming)

(Colotrechinae)-- (plant gall-forming)

(Cratominae)-- (probably parasites of wood-boring beetles)

(Diparinae)-- (parasites of beetles on shrubs or in soil)

(Ditropinotellinae)-- (plant gall-forming)

(Elatoidinae)-- (parasites of scale insects)

(Erotolepsiinae)-- (rare & habits unknown)

(Eunotinae)-- (predators of scale insect eggs & rarely aphids & psyllids; some hyperparasites)

(Eutrichosomatinae)-- (parasites of curculionid beetles)

(Herbertinae)-- (parasites of leaf-mining Diptera)

(Keiraninae)-- (parasites of margarodid scale insects)

(Leptofoeninae)-- (probably parasites of wood-boring beetles)

(Louriciinae)-- (parasites of cerambycid beetle eggs)

(Macromesinae)-- (parasites of curculionid & scolytid beetles)

(Miscogasterinae)-- (a few species predators or parasites of fly larvae)

(Nefoeninae)-- (rare & habits unknown)

(Neodiparinae)-- (rare & habits unknown)

(Ormocerinae)-- (plant gall-forming & parasites of other gall-formers)

(Panstenoninae)-- (probably parasites of insect eggs & larvae in grass stems)

(Parasaphodinae)-- (parasites of scale insects)

(Pireninae)-- (parasites of cecidomyiid flies)

(Pteromalinae)-- (parasites of other insects)

(Spalangiinae)-- (parasites of Diptera primarily)

(Storeyinae)-- (rare & habits unknown)

Rotoitidae ("rotoitid wasps," 2 species)

Signiphoridae ("signiphorid wasps," 82 species hyperparasitic on Homoptera--often included with Encyrtidae)

Tanaostigmatidae ("tanaostigmatid wasps," 92 species, plant gall-forming)

Tetracampidae ("tetracampid wasps," 53 species parasitic on Coleoptera, Diptera & Hymenoptera)

Torymidae ("torymidid wasps," 1,156 species parasitic on other insects)

(Megastigminae, Monodontomerinae, Sycophaginae, Toryminae)

Trichogrammatidae ("trichogrammatid wasps," 678 species parasitic on eggs of mainly Lepidoptera)

Cynipoidea

Charipidae ("charipid wasps," 212 species, hyperparasites of Homoptera)

Cynipidae ("gall wasps," probably >2,000 species, plant-feeding in galls)

Eucoilidae ("eucoilid wasps," probably >450 species, internal parasites of flies)

Figitidae ("figitid wasps," 253 species, parasitic in larvae of Diptera)

Ibaliidae ("ibaliid wasps," 17 species, parasites of wood wasp larvae)

Liopteridae ("liopterid wasps," 71 species, probably parasites of wood-boring beetles)

Evanioidea

Aulacidae ("aulacid wasps," 150 species, parasites of wood-boring Coleoptera & Hymenoptera)

Evaniidae ("evaniid wasps," 410 species, parasites of cockroach eggs)

Gasteruptiidae ("gasteruptid wasps," 512 species, parasites of solitary wasps & bees)

Ichneumonoidea

Agriotypidae ("agriotypid wasps," few species parasites of caddis flies)

Aphidiidae ("aphidiid wasps," 800 species parasitic in aphids)

Apozygidae ("apozygidid wasps")

Braconidae ("braconid wasps," 40,250 species parasites of Lepidoptera larvae, but Diptera, Coleoptera & spiders also)

Ichneumonidae ("ichneumonid wasps," 60,200 species parasites of many insects)

Paxylommatidae ("paxylommatid wasps")

Proctotrupoidea

Diapriidae ("diapriid wasps," 2,410 species, parasites of Diptera)

Heloridae ("heloridid wasps," 7 species, parasites of lacewings)

Monomachidae ("monomachid wasps," 21 species, parasites of flies)

Pelecinidae ("pelecinid wasps," one parasite of scarab beetle larvae)

Platygastridae (= Platygasteridae) ("platygasterid wasps," 1,125 species parasites of Diptera & Homoptera)

Proctotrupidae ("proctotrupid wasps," 352 species, parasites of beetle & fly larvae)

Roproniidae ("roproniid wasps," 18 species)

Scelionidae ("scelionid wasps," 3,021 species parasites of insect eggs & occasionally spider eggs)

Sphecidae ("sphecid wasps," 660 species)

Trupochalcididae ("trupochalcidid wasps")

Vanhorniidae ("vanhorniid wasps," 1 species parasitic on beetle larvae)

Stephenoidea

Stephanidae ("stephanid wasps," 112 species, rare parasites of wood-boring insect larvae)

Trigonalyoidea

Trigonalyidae ("trigonalyid wasps," 76 species, a few parasites of Hymenoptera & Diptera)

LEPIDOPTERA (moths & butterflies, 156,000 species)

Blastobasidae ("blastobasid moths," some larvae internal parasites of scale insects)

Cosmopterygidae (a few internal parasites of scale insects)

Cyclotornidae (some larvae are predators of leafhoppers)

Epipyropidae ("planthopper parasites"; some larvae parasites of Homoptera)

Heliodinidae (some predators of scale insects & spider eggs)

Lycaenidae ("coppers & hair streaks," some larvae predators of aphids and scale insects)

Noctuidae ("owlet or cutworm moths," some general predators of scale insects)

Oinophilidae (a few larval predators of scale insects)

Olethreutidae (some larvae predators of scale insects)

Phycitidae (some larvae predators of Lepidoptera pupae & scale insects)

Psychidae ("bagworms," some larvae predators of scale insects)

Pyralidae ("snout & grass moths")

(Chrysauginae)-- (parasite/predators of caterpillars)

Pyraustidae (some larval predators of Lepidoptera eggs)

Tortricidae ("leaf-roller moths," some larval predators of scale insects)

MALLOPHAGA ("chewing lice," 3,421 species, external parasites of birds & some mammals)

MECOPTERA ("scorpion flies," 512 species, adults predators of flies, primarily)

MICROCORYPHIA ("jumping bristletails," 312 species, plant-feeding)

NEUROPTERA ("alderflies, fishflies, lacewings, snakeflies," 7,200 species)

Apochrysidae ("apochrysids")

Ascalaphidae ("false ant lions & owl flies," general predators)

Berothidae ("beaded lacewings," larvae are predators of other insects)

Chrysopidae ("green lacewings," predators of soft-bodied insects)

Coniopterygidae ("dusty wings," predators of plant-feeding mites & some Homoptera)

Corydalidae ("dobson flies, fishflies," probably general predators)

Dilaridae ("pleasing lacewings," larvae are predators of other insects)

Hemerobiidae ("brown lacewings," predators of Homoptera)

Inocelliidae ("inocellids," probably general predators)

Ithonidae ("ithonids," probably general predators of soft-bodied insects)

Mantispidae ("mantid flies," general predators; larvae feed on spider eggs)

Myiodactylidae ("myiodactylids," predators of other insects in trees)

Myrmeleontidae ("ant lions," general predators)

Nemopteridae ("nemopterids," predators of other insects)

Nymphidae ("nymphids," predators of wood ants)

Osmylidae ("osmylids," larvae predators of flies in wet places)

Polystoechotidae ("giant lacewings," larvae terrestrial predators)

Psychopsidae ("psychopsids," larvae are predators of tree-inhabiting insects)

Raphidiidae ("snake flies," general predators)

Sialidae ("alder flies," larvae are predators of other aquatic insects)

Sisyridae ("spongillaflies," aquatic larvae may feed on insects in freshwater sponges)

Stilbopterygidae ("stilbopterygids")

Sympherobiidae ("sympherobiids")

Trichomatidae ("trichomatids")

ODONATA ("dragonflies, damselflies," 6,300 species, adults & nymphs are general predators)

ORTHOPTERA ("cockroaches, crickets, grasshoppers, preying mantids," 32,000 species)

Gryllacridae ("gryllacrid hoppers," predators of beetles)

Gryllidae ("gryllid hoppers," some predators of aphids & scale insects)

Mantidae ("preying mantids," general predators of insects)

Tettigonidae ("longhorn grasshoppers"; predators of other insects)

PLECOPTERA ("stoneflies," 2,112 species, some predators of other insects)

PROTURA ("proturans," 193 species, scavengers or plant-feeding)

PSOCOPTERA ("psocids," 1,893 species, some may be predators of mealybugs)

SIPHONAPTERA ("fleas," 1,820 species, scavengers & blood-sucking)

STREPSIPTERA ("twisted-winged parasites," parasites of Hemiptera, Homoptera, Hymenoptera & Orthoptera)

(Callipharixenidae, Elenchidae, Halictophagidae, Mengeidae, Myrmecolacidae, Stichotrematidae, Stylopidae)

THYSANOPTERA ("thrips," 5,300 species, some predators of plant-feeding mites, insect eggs & scale insects)

THYSANURA ("bristletails, silverfish," 412 species, a few may be predators of termites)

TRICHOPTERA ("caddis flies," 5,612 species, a few larvae are predators of other insects)

ZORAPTERA ("zorapterans," 39 species, scavengers & plant-feeding)

Nature of Insect Parasitism

Parsitic insects are organisms which live in, on or at the expense of another organism. Parasitism may be viewed as a form of symbiosis involving at least two unrelated species. One symbiont (the parasite) lives at the expense of the other symbiont (the prey). The parasite provides no obvious benefit to the prey and eventually destroys it. Parasitism is complex and the animals which participate in this lifestyle function as primary, secondary, facultative, obligatory, external or internal parasites.

Insects which develop as parasites have been called protelean parasites (Askew 1971) in contrast to other groups of organisms which develop parasitically. The term parasitoid was proposed for insects which develop in this manner (Reuter 1913), and it has gained acceptance among ecologically and behaviorly oriented workers. Parasitism in insects may be viewed as a transitional condition between predation and true parasitism in the classical sense. The parasitic larva is usually parasitic during the early stages, and predatory during later development.

Attributes of protelean parasites which distinguish them from other parasitic animals are (1) parasitical behavior is expressed only during the larval stage, (2) the adult stage is free living (3) the parasite larva typically kills and consumes one prey, (4) body size of the parasitic insect approximates that of the prey, (5) the life cycle is relatively simple, and (6) the parasitic insect parasitizes members of its own class.

Parasitic insects display a prodigious array of reproductive strategies. Basically parasitic insects may develop internally (endoparasites), externally (ectoparasites) or they may develop initially as internal parasites and complete development externally. Additionally there are numerous variations which are influenced by ecological habitat, adult female anatomy, oviposition behavior, prey taxa, prey biology and numerous other factors.

The term idiobiont has been proposed for protelean parasites which kill, permanently impair or paralyze their prey after oviposition and thereby prevent further development of the prey. Typically, idiobionts are ectoparasites which attack prey in concealed situations and which express a broad prey spectrum (= generalists). koinobiont has been proposed for protelean parasites which do not kill, permanently impair or paralyze their prey after oviposition and thereby do not prevent further development. They are typically endoparasitic and attack prey in exposed situations, thereby demonstrating a limited range of prey (= specialists). Price (1977) discussed aspects of the evolutionary biology of parasitic insects.

Occurrence of Parasitism in Insects

Insect parasitism is focused on several orders of insects, including Coleoptera (beetles), Diptera (flies), Hymenoptera (bees, wasps), Lepidoptera (moths and butterflies), and Strepsiptera (twisted-winged insects). Hymenoptera are the most important group of insects in applied biological control. Hence, most of the following discussion involves this order. Presently the Hymenoptera contain about 200,000 known species, but the existing number is substantially larger, based on the large number of species awaiting description. Ecologically the Hymenoptera are exceeding diverse.

Features distinguishing Hymenoptera include mandibulate (= chewing) mouthparts in larva and adult, adult with four membranous wings, forewing largest and connected to the hindwing with hook-like hamuli which are engaged only during flight, and females have an ovipositor that functions as an appendage. The order includes the suborders Symphyta (Chalastogastra) (= sawflies, woodwasps) and Apocrita (Clistogastra) (= bees, wasps, ants).

In biological control the Symphyta assume a minor position because nearly all species are plant-feeding. Parasitism is restricted to one family, the Orussidae, which is cosmopolitan in distribution and contains about 85 species which apparently develop as external parasites of beetles feeding in tree trunks. One species of Orussus has been used with some effectiveness in applied biological control.

The Apocrita are numerically more abundant and impact to a significant extent the populations of other insects.