Parasitoid wasp: Difference between revisions
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In endoparasitoids, host immune cells can encapsulate the the eggs and larvae of parasitoid wasps. In [[aphid]]s, the presence of a secondary endosymbiont,[[Buchnera aphidicola]] that carries a particular latent phage makes the aphid relatively immune to their parasitoid wasps by killing many of the eggs. However, wasps counter this by laying more eggs in aphids that have the endosymbiont so that atleast one of them can hatch and parasitize the aphid.<ref>{{cite doi|10.1073/pnas.0335320100 }}</ref><ref>{{cite doi|10.1186/1741-7007-10-11}}</ref> |
In endoparasitoids, host immune cells can encapsulate the the eggs and larvae of parasitoid wasps. In [[aphid]]s, the presence of a secondary endosymbiont,[[Buchnera aphidicola]] that carries a particular latent phage makes the aphid relatively immune to their parasitoid wasps by killing many of the eggs. However, wasps counter this by laying more eggs in aphids that have the endosymbiont so that atleast one of them can hatch and parasitize the aphid.<ref>{{cite doi|10.1073/pnas.0335320100 }}</ref><ref>{{cite doi|10.1186/1741-7007-10-11}}</ref> |
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[[Drosophila melanogaster]] females lay their eggs in food containing toxic amounts of alcohol if they detect prasioid wasps nearby. Despite the alcohol retarding the growth of the flies, it protects them from the wasps.<ref>{{cite doi|10.1126/science.1229625}}</ref> |
Certain caterpillars eat plants that are toxic to both themselves and the parasite to cure themselves.<ref>{{cite doi|10.1371/journal.pone.0004796}}</ref> [[Drosophila melanogaster]] larvae also ''self-medicate'' with ethanol to treat parasitism.<ref>{{cite doi| 10.1016/j.cub.2012.01.045}}</ref> D. melanogaster females lay their eggs in food containing toxic amounts of alcohol if they detect prasioid wasps nearby. Despite the alcohol retarding the growth of the flies, it protects them from the wasps.<ref>{{cite doi|10.1126/science.1229625}}</ref> |
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==See also== |
==See also== |
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Revision as of 15:36, 22 February 2013
 | This article needs more links to other articles to help integrate it into the encyclopedia. (December 2012) |
The term parasitoid wasp refers to a large evolutionary grade of hymenopteran superfamilies, mainly in the Apocrita*. Parasitic Apocrita is divided into 11 subfamilies. The adults can be distinguished by the character of the pronotum, antennae and ovipositor, number of trochanter segments, and the wing venation (Borror and White). They are primarily parasitoids of other animals, mostly other arthropods and are typically represented by the families Ichneumonidae and Braconidae. It also may include wasps in the family Aphelinidae. Many of them are considered beneficial to humans because they control populations of agricultural pests while having little to no effect on crops.
Description
Many species are very small even as adults ranging from 1/100 to ¾ inch long (Drees and Jackman). Most females have a ‘spine-like’ ovipositor at the tip of the abdomen (Drees and Jackman). The egg and larval stage are usually not observed unless dissected from the host in which the adult female parasitized.
Distinguishing features: Ichneumonidae and Brachonidae
Brachonidae
Most are brownish or black, not brightly colored (Borror and White). These species are widely distributed. They also have a wide range of hosts in which they parasitize. Some species of Brachonids pupate in silken cocoons on the outside of their dead host (Miller and Ball). Wing venation: Only one recurrent vein, or no recurrent veins.
Ichneumonidae
Ichneumonids vary greatly in size and color from brightly colored yellow to uniform black. These species are also widely distributed. Many are very specific in the species of the host they parasitize. Wing venation: Two recurrent veins.
Parasitism
Hosts
While caterpillars are a prime example of a larval lepidopteran host, parasitoid wasps can parasitize all life stages [egg, larva, adult] and parasitize most other orders of insects including Coleoptera, Diptera, Hemiptera and other Hymenoptera. Adult female wasps parasitize other insect species by ovipositing into their hosts. The female also inserts secretory products [a combination of polydnaviruses, ovarian proteins, and venom] in with the egg to protect it from the immune system of the host (Miller and Ball). Once a host has been parasitized, the virus, that accompanied the egg during oviposition, alternates the physiology of the host to benefit the parasitoid and the viral genes are expressed by the host organism (Marziano and Hasegawa).
Life Cycle
The egg hatches inside of the host into a larva. The parasitoid larva, by feeding on the inside of the host, then develops into a more mature larvae ready for pupation and eats its way out of the dying or dead host. It then spins a cocoon and pupates (Miller and Ball). As an adult, it feeds primarily on nectar from flowers and all adult females have their own unique version of the polydnavirus in their oviducts.
Description
Polydnaviruses are a unique group of insect viruses that have a mutualistic relationship with some parasitic wasps. Wasps benefit from this mutualism because the virus provides certain protection of the parasitic larva inside the host by weakening the host’s immune system and by altering the cells of the host to be more beneficial to the parasite. The polydnavirus, like all viruses, need a host to replicate and in this case is the oviducts of the adult female. The relationship between these viruses and the wasp is obligatory in the sense that all individuals are ‘infected’ with the viruses; the virus has been incorporated in the wasp’s genome (Miller and Ball). These relationships between virus and parasitoid have been and are currently studied as model systems to study parasitoid-host immune interactions (Beckage).
Mechanisms
Some species have direct aggressive mechanisms for parasitizing a host by actively targeting the host immune system and then suppressing it; polydnaviruses are responsible for this approach (Miller and Ball). Others have more passive approaches to parasitism by ovipositing into a part of the host that has little exposure to the host’s immune system or by avoiding activation of the host’s immune system (Miller and Ball); ovarian proteins are more involved in this approach and PDV less so.
Evolution
There are two especially recognized genera of polydnaviruses: Ichnoviruses (IV) and Bracoviruses (BV). The ichnoviruses occur in ichneumonid wasp species and bracoviruses in braconid wasps. The genome of the virus is composed of multiple segments of double-stranded, super-helical DNA packaged in capsid proteins and a double layer (IV) or single layer (BV) envelope. The large genome of polydnaviruses is what distinguishes PDV from other viruses (Feming and Summers). While both have segmented DNA genomes, little or no sequence homology exists between BV and IV, suggesting that the two genera evolved independently. Specifically, BV and IV radically differ in morphology, methods of nucleocapsid release from cells, and possible packaging of multi-genomic DNAs; it is also unknown whether the two follow the same strategy of replication (Wanjiru).
Pest Control
Typically, parasitoid wasps are not considered agricultural pests and are considered a beneficial insect as they control the population of host insects. They are also increasingly being released directly into regions specifically for the use of agricultural pest control.
“A number of parasitic wasp species are commercially available from insectaries and are purchased and released in augmentative biological control programs. Other species have been imported from other countries from which pests have been accidentally introduced without their natural enemies and released to reintroduce the natural enemy with its host, a practice called importation, or "classical" biological control and which occasionally results in sustained suppression.” (Drees and Jackman)
Host defenses
The hosts of parasitoids have several levels of defense against them. Many hosts try to hide from the parasitoids in inaccessible habitats. They may also get rid off their frass (body wastes) and avoid plants that they have chewed on as both can attract parasitoids. The egg shells and cuticles of the prey are thickened to prevent the parasitoid from penetrating them. When they encounter the egg laying female, prey use defenses like dropping off the plant they are on, twisting and thrashing so as to dislodge or kill the female and even regurgitating onto the wasp to entangle it. [1][2] The wriggling can sometimes help by causing the wasp to "miss" laying the egg on the host and instead place it nearby. Wriggling of pupae can cause the wasp to lose its grip on the smooth hard pupa or get trapped in the silk strands. Some caterpillars even bite the female wasps that approach it. Some insects secrete poisonous compounds that kill or drive away the parasitoid. Ants that are in a symbiotic relationship with caterpillars, aphids or scale insects may protect them from attack by wasps.
Even parasitoid wasps are vulnerable to hyperparasioid wasps. Some parasitoid wasps change the behaviour of the infected host to build a silk web around the pupa of of the wasps after they emerge from its body to protect them from hyperparasitoids.[3]
In endoparasitoids, host immune cells can encapsulate the the eggs and larvae of parasitoid wasps. In aphids, the presence of a secondary endosymbiont,Buchnera aphidicola that carries a particular latent phage makes the aphid relatively immune to their parasitoid wasps by killing many of the eggs. However, wasps counter this by laying more eggs in aphids that have the endosymbiont so that atleast one of them can hatch and parasitize the aphid.[4][5]
Certain caterpillars eat plants that are toxic to both themselves and the parasite to cure themselves.[6] Drosophila melanogaster larvae also self-medicate with ethanol to treat parasitism.[7] D. melanogaster females lay their eggs in food containing toxic amounts of alcohol if they detect prasioid wasps nearby. Despite the alcohol retarding the growth of the flies, it protects them from the wasps.[8]
See also
- Tachinidae a group of parasitoid flies.
References
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Beckage, N.E. (2008). Insect Immunology. Elsevier’s Science and Technology Rights Department.
Borror, D. J. & White, R. E. (1970). Insects. Peterson Field Guide. Houghton Mifflin Company.
Drees, B.M. & Jackman, J. (1999). Parasitic Wasp. Field Guide to Texas Insects. Gulf Publishing Company.
Dupas, S., Wanjiru, G., Branca, A., Pierre Le Ru, B. & Silvain, J. (2008). Evolution of a Polydnavirus Gene in Relation to Parasitoid–Host Species Immune Resistance. Oxford Journals 99, 491-499.
Jo-Ann G., Feming, W. & Summers, M.D. (1991). Polydnavirus DNA is integrated in the DNA of its parasitoid wasp host. Proceedings of the national academy of sciences 88, 9770-9774.
Miller, L.K & Ball, L.A. (1998). The Insect Viruses. The Viruses.
Marziano, N.K., Hasegawa, D.K., Phelan, P & Turnbull, M.W. (2011) Functional Interactions between Polydnavirus and Host Cellular Innexins. Journal of Virology 85, 10222-10229