Host confusion and the evolution of insect diet breadths

Many herbivorous insects develop well, or even better, on hosts which they will not use than on hosts they regularly use. A verbal model explains this often imperfect correlation between host use and host suitability. The model focuses on limitations in an insect's ability to perceive and integrate host-associated stimuli. Confusion of "good' hosts with "poor' hosts results from an imperfect identification process and will result in selection for either a change in the behavioral response of an insect to host associated stimuli, or a change in the insect's ability to perceive and integrate these stimuli. There are four evolutionary solutions for dealing with the confusion of "good' and "poor' hosts. 1) Insects may continue to use both hosts, despite selection against use of "poor' hosts, 2) Insects may evolve the machinery to distinguish "good' from "poor' hosts; 3) Insects may evolve physiological, morphological, or other characters which increase their fitness on the "poor' hosts. 4) Insects may delete the hosts which are difficult to distinguish from the diet, either by restricting oviposition to other plants currently utilized, or by shifting to a new host (or suite of hosts) which has characteristic signature and is therefore distinguishable from poor quality hosts. This final option will result in insects avoiding oviposition on plants that are suitable for larval development. -Author