13.3. Prey/host selection and specificity

As we have seen in Chapters 911, insects vary in the breadth of food sources they use. Thus, some predatory insects are monophagous, utilizing a single species of prey; others are oligophagous, using few species; and many are polyphagous, feeding on a variety of prey species. As a broad generalization, predators are mostly polyphagous, as a single prey species rarely will provide adequate resources. However, sit-and-wait (ambush) predators, by virtue of their chosen location, may have a restricted diet — for example, antlions may predominantly trap small ants in their pits. Furthermore, some predators select gregarious prey, such as certain eusocial insects, because the predictable behavior and abundance of this prey allows monophagy. Although these prey insects may be aggregated, often they are aposematic and chemically defended. Nonetheless, if the defenses can be countered, these predictable and often abundant food sources permit predator specialization.

Predator—prey interactions are not discussed further; the remainder of this section concerns the more complicated host relations of parasitoids and parasites. In referring to parasitoids and their range of hosts, the terminology of monophagous, oligophagous, and polyphagous is applied, as for phytophages and predators. However, a different, parallel terminology exists for parasites: monoxenous parasites are restricted to a single host, oligoxenous to few, and polyxenous ones avail themselves of many hosts. In the following sections, we discuss first the variety of strategies for host selection by parasitoids, followed by the ways in which a parasitized host may be manipulated by the developing parasitoid. In the final section, patterns of host use by parasites are discussed, with particular reference to coevolution.

Chapter 13