Parasitoid host preference

The diet of the host may play a significant role in host preference. Hendry et al. (1976) reported that corn contains tricosane, the kairomone for Tricho-gramma evanescens which was first isolated from Heliothis zea, a com feeder. Sauls et al. (1979) reported that the frass of H. zea reared on different diets differed significantly in its kairomonal activity for Microplitis croceipes. Thus, the preference for a given host may be influenced by the food consumed by the host, possibly, a particular host might be able to escape parasitoidism by feeding on certain plants or food resources. 

The nematodes are themselves insect parasitoids that are not very particular about their hosts. Fly maggots, moth larvae and pupae, beetle larvae, and numerous other hosts are all acceptable to them. Some of these nematodes do have narrow preferences, but one widespread species invades more than two hundred different kinds of insects. Juvenile nematodes infected with their bacteria seek out a host to parasitize, typically gaining entry through one of its body orifices. Some species enter through a hole they scrape in the insect s cuticle using a "tooth" on their head. Once inside the insect, the worms force their way through soft tissues and into their host s central body cavity. 

Toxic substances acquired from the host plaint may provide resistance to parasitoids (24), pathogens (25), and predators (45). By avoiding some toxins in plant material and selecting superior food tissues, insects feeding on variable hosts may become more susceptible to some enemies. Of course, other substances in preferred tissues may still be toxic to certain of these enemies, but this is less likely than it would be were plant compounds uniformly encountered by the host insect. 

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