Interspecific Host Discrimination Research Articles

Intra- and Interspecific Host Discrimination in Telenomus podisi and Trissolcus euschisti (Hymenoptera: Scelionidae)

Telenomus podisi Ashmead and Trissolcus euschisti (Ashmead) are sympatric scelionid stink bug egg parasitoids whose intraspecific host discrimination is based on external post-ovipositional host egg markings. There is no interspecific host discrimination. The marking pheromone is not as strong an ovipositional deterrent 96–100 h after it is deposited, as it is 0–1 h after deposition. In T. euschisti this compound is water soluble.

The function of host discrimination and superparasitization in parasitoids.

Host discrimination, i.e. the ability to distinguish unparasitized hosts from parasitized ones, and to reject the latter for egg laying is present in many parasitic wasp species. This property is classically considered as an example of contest competition, and is supposed to have a number of functions. However, different species do not react to each other's marks and lay eggs in hosts parasitized by the other species. Apparently the marks used for recognition are specific.Multiparasitization is the best strategy when hosts are scarce and the egg supplies of the parasitoids are not limited. Interspecific host discrimination is not an ESS.Superparasitization within one species would have selective advantage if the number of unparasitized hosts is small and the wasp has a reasonable chance to lay her egg in a host that is not parasitized by herself, and if the chance for her offspring to survive the competitive battle with the first parasitoid larva is not too small. This is shown to be the case.However, marks are not individual and wasps cannot distinguish hosts parasitized by themselves from those parasitized by others. The hypothesis is tested that the egg laying strategy (i.e. the decision to superparasitize) of wasps is dependent on the number of conspecifics that is searching simultaneously for hosts, since this determines the chance that a parasitized host encountered by a wasp is parasitized by herself.It is shown that host discrimination cannot be regarded as a case of contest competition. Other aspects of superparasitization, related to interference and population regulation, sex allocation and encapsulation are briefly discussed.

Why is there no interspecific host discrimination in the two coexisting larval parasitoids of Drosophila species; Lepyopilina heterotoma (Thomson) and Asobara tabida (Nees).

(1) The parasitic wasps Leptopilina heterotoma (Thomson) and Asobara tabida (Nees) usually refrain from laying eggs in hosts that have already been parasitized by themselves or by a conspecific (=intraspecific host discrimination). (2) In contrast to intraspecific host discrimination, interspecific host discrimination, in which females refrain from laying eggs in hosts that have already been parasitized by the other species, is not found in these sympatric parasitid species. (3) Because we expected that development of interspecific host discrimination would increase the fitness of the wasps, we wondered why this strategy had not evolved in L. heterotoma and A. tabida. (4) We therefore developed a simulation model of the parasitization process, in which interspecific host discrimination can be included. (5) By varying the time needed for host location, survival chances and the proportions of hosts parasitized, we obtained estimates for the number of offspring in situations with and without interspecific host discrimination. (6) The results imply that, assuming that female wasps carry an ample supply of eggs, the development of interspecific host discrimination by L. heterotoma or A. tabida will not lead to increased fitness, even under extreme circumstances. Hence, interspecific host discrimination will not evolve.

Intra- and interspecific host discrimination in Asobara (Hymenoptera) larval endo-parasitoids of Drosophilidae: Comparison between closely related and less closely related species

Host discrimination studies were conducted with different species of Asobara, which are larval endo-parasitoids of Drosophilidae. Results indicated variable host discrimination which depended on the relatedness of the species. The closely related sibling species Asobara tabida (Nees) and A. rufescens (Foerster) were not only capable of intraspecific discrimination, but also avoided multiparasitism by discriminating between unparasitized host larvae and larvae previously parasitized by females of the other species. This ability to discriminate interspecifically does not seem functional as each species occupies its own microhabitat. As it was shown to be absent in less closely related Asobara species we concluded that interspecific discrimination by A. tabida and A. rufescens was due to their close relationship.