Taste sensitivity of insect herbivores to deterrents is greater in specialists than in generalists: A behavioral test of the hypothesis with two closely related caterpillars

Sensitivity of caterpillars of Heliothis virescens, a generalist, and H. su bflexa, a specialist, to eight different plant secondary compounds was exam ined behaviorally. The compounds were nicotine hydrogen tartrate, hordenine , caffeine. sinigrin, linamarin, arbutin, chlorogenic acid, and salicin. Al l compounds deterred feeding, at least at the higher concentrations, but th e generalist was less affected than the specialist. Thus the hypothesis tha t specialists have greater sensitivity to deterrents than generalists was s upported. In most cases deterrence occurred on first encounter, indicating that the response was sensory; in some cases short-term postingestive effec ts also appeared to play a role. The larger quantities of deterrent-contain ing food ingested by H. virescens sometimes resulted in measurable postinge stive effects during the second control test. This did not occur in H. subf lexa, which more commonly rejected the deterrent-containing food on first c ontact. The contrast between the species is discussed in relation to tradeo ffs involved in different diet breadths.