Host plant acceptance in a generalist insect: threshold, feedback or choice?

Abstract Generalist insect herbivores feed mainly on one or more primary host species, but unlike specialists they also accept numerous secondary hosts. This raises the question of how generalists retain a broad host range yet allocate most of their eggs to primary hosts. We considered three possible explanations. (1) Threshold: secondary hosts are accepted less readily than primary hosts. (2) Feedback loop: insects ovipositing on primary hosts lay subsequent eggs faster than on secondary hosts. (3) Choice: insects compare plant cues sensed over a certain period and oviposit on preferred plants. We measured time and number of landings leading to egg-laying in a generalist moth, Helicoverpa punctigera , on a primary host and two secondary hosts and recorded subsequent egg-laying rates on each. The moths typically accepted only the primary host on the first landing and laid subsequent eggs on this host earlier in the night, indicating thresholds and feedback operate together.