Many wasps and some flies develop as parasites. With these insects the adult female seeks a host insect for their young. They then lay an egg in or on this host which the developing young consume. Life cycles of these parasites and their host are very closely synchronized and the larvae may not kill their host for a long period, maintaining itself on a diet of non-vital tissues. Ultimately they are lethal to the host.
Most parasite larvae develop inside their host and are not observed. (A few, notably in the wasp family Eulophidae, may have stages that feed on the outside of the host.) However, larvae of many parasites emerge from the host when feeding is completed and pupate on the outside, allowing them to be observed. Adult parasites usually feed on nectar, pollen, and honeydew; a few feed on blood of host insects which they puncture with their ovipositor.
Diptera: Tachinidae
The tachinid flies are a large (ca 1300 North American species) and very important family of parasitic flies. All develop as internal parasites of other insects including many caterpillars, beetles, true bugs, earwigs and grasshoppers that occur as garden pests. Typical species somewhat resemble house flies but tend to have more stout, bristly hairs on the abdomen. However, there are some very tiny tachinid flies that develop in small insects (e.g., Phasia occidentis from false chinch bug).
Females usually parasitize host insects by gluing an egg to the body, often near the head. However, some tachinid flies insert larvae directly onto the host insect. Adults feed on nectar and pollen.
Some of the more important tachinid flies present in the region and their hosts are:
|
Tachinid fly |
Hosts |
|
Phasia occidentis |
False chinch bug |
|
Compsilura concinnata |
Various caterpillars |
|
Trichopoda pennipes |
Squash bug |
|
Doryphorophaga doryphoryae |
Colorado potato beetle |
|
Voria ruralis |
Loopers, armyworms, cutworms |
|
Lespesia sp. |
Imported cabbageworm |
|
Peleteria spp. |
Cutworms, armyworms |
|
Celatoria diabroticae |
Cucumber beetles |
Hymenoptera: Ichneumonidae
Ichneumonid wasps are some of the larger parasitic wasps. Most are fairly slender wasps with very long antennae. Females usually possess a long and conspicuous ovipositor. Most ichneumonid wasps associated with crop pests are parasites of caterpillars. Common genera include Hyposoter, Diadegma, Ophion, Itoplectis and Exochus.
|
Ichneumon Wasp |
Hosts |
|
Bathyplectes anurus |
Alfalfa weevil |
|
Bathyplectes curculionis |
Alfalfa weevil |
|
Diadegma insulare |
Diamondback moth |
|
Patracloides mantanus |
Cabbage looper |
|
Hyposoter spp. |
Cutworms, loopers |
Hymenoptera: Braconidae
In overall body form they often resemble ichneumonid wasps but are usually much smaller. Bracon, Chelonus, Leiophron, Macrocentrus and Opius are common genera. The white or yellowish pupae of Cotesia species, which are spun on or adjacent to their caterpillar host, are among the most commonly observed stages of any parasitic wasp.
|
Braconid Wasp |
Hosts |
|
Cotesia glomerata |
Cabbageworms |
|
Cotesia medicaginis |
Alfalfa caterpillar |
|
Cotesia laeviceps |
Armyworm |
|
Apanteles congregatus |
Hornworms |
|
Macrocentrus incompletus |
Cutworms |
|
Microctonus aethiopoides |
Alfalfa weevil |
|
Meteorus communis |
Cutworms, armyworms |
|
Microplitis croceipes |
Corn earworm, tobacco budworm |
|
Perilitis coccinellae |
Lady beetles |
|
Peristenus digoneutis |
Lygus spp. |
|
Leiophron uniformis |
Lygus spp. |
Hymenoptera: Aphidiidae
Aphid parasites are among the most ubiquitous of the parasitic wasps, found almost invariably among aphid colonies. As the wasp develops within the aphid the host typically swells, becomes lighter in color and affixed to the leaf. Aphids killed in this manner are often referred to as "aphid mummies". A circular hole cut by the emerging wasp also is characteristic. Among the more common genera of aphid wasps are Trioxys, Diaeretiella, Lysiphlebus, and Aphidius.
|
Aphid Parasite |
Hosts |
|
Lysiphlebus testaceipes |
Greenbug, other aphids |
|
Diaeretiella rapae |
Green peach aphid, cabbage aphid, Russian wheat aphid, others |
|
Aphidius matricariae |
General aphid parasitoid |
|
Aphidius ervi |
General aphid parasitoid |
Hymenoptera: Encyrtidae
Among the tiniest of the parasitic Hymenoptera are the encyrtids. They develop internally in eggs, larvae or pupae of certain insects. An unusual species is Copidosoma truncatellum, which lays its eggs in the eggs of cutworms, loopers and other caterpillars. The species is polyembryonic and numerous larvae - sometimes over 1000 - develop from the few eggs originally laid. The larvae of this wasp develops throughout the larval live of the caterpillar host, killing it as it prepares to pupate.
Within the encyrtids are the aphelinid wasps (Aphelininae), which include many important species that attack insects in the order Homoptera. Several Encarsia species are very important as parasites of whiteflies and cause the host nymph to turn black when parasitized. Aphelinus is a genus that includes important parasites of aphids, which also characteristically turn dark black when parasitized.
|
Encyrtid Wasp |
Hosts |
|
Copidosoma truncatellum |
Cutworms, loopers |
|
Aphelinus albipodus |
Russian wheat aphid |
|
Aphelinus asychis |
Russian wheat aphid |
|
Aphelinus varipes |
Russian wheat aphid |
Hymenoptera: Encyrtidae
Most chalcid wasps (Chalcididae family) are internal parasites of caterpillars, although some develop in fly larvae. They are distinguished by having very enlarged femurs on the hind legs.
|
Chalcid Wasp |
Host |
|
Brachymeria intermedia |
Large caterpillars (pupal parasitoid) |
Hymenoptera: Eulophidae
Eulophid wasps are very small (typically ca. 1/25-inch) and, along with braconids, are the most important of the parasitic wasps in many agricultural crops. Several kinds of agricultural insects are attacked by eulophid wasps including caterpillars, beetle larvae, psyllids and leafminer flies. Adults of some species (e.g. Tetrastichus) kill eggs and small immature insects as they feed, acting as predators. Some eulophids develop as external parasites of caterpillars, and may occur as groups on the body of the host (Euplectrus spp.).
|
Eulophid Wasp |
Host |
|
Tetrastichus asparagi |
Asparagus beetle |
|
Tetrastichus triozae |
Potato/tomato psyllid |
|
Tetrastichus incertus |
Alfalfa weevil |
|
Tetrastichus julis |
Cereal leaf beetle |
|
Euplectrus plathypenae |
Corn earworm, loopers, cutworms, other caterpillars |
|
Diglyphus websteri |
Vegetable leafminer |
Hymenoptera: Trichogrammatidae, Mymaridae
The smallest parasitic wasps - and smallest insects known - are those that develop as internal parasites of insect eggs. The trichogramma wasps (Trichogrammatidae family) are well known as parasites of caterpillar eggs and are widely available for sale in use for biological control. Even more minute are the fairy flies (Mymaridae family). These include the genus Anagrus, important in managing leafhoppers, and Anaphes, which include parasites of Lygus bug eggs.
Categories: Biological Control, Insects, Insect Parasitoids, Tachinid Flies, Ichneumonid Wasps, Braconid Wasps, Aphid parasites, Encyrtid wasps, Chalcid wasps, Eulophid Wasps, Egg Parasitoids
Date: 05/11/2004
