Influence of previous herbivory on behavior and development of Spodoptera exigua larvae on glanded and glandless cotton

We examined the influence of previous herbivore injury on the feeding behav ior, survival and development of larval beet armyworm, Spodoptera exigua Hu bner (Lepidoptera: Noctuidae), on glanded and glandless `Stoneville 213' co tton, Gossypium hirsutum L. In a greenhouse study, neonate S. exigua placed on the terminal foliage of glanded cotton plants moved down the plant to f eed on older leaves. The location of feeding was more concentrated towards the bottom of the plant on previously damaged plants than on undamaged cont rol plants. In contrast, larval feeding on glandless plants was evenly dist ributed within the plant and no difference in distribution was noted on pla nts that had sustained previous herbivore injury when compared to undamaged plants. In a laboratory study, where larvae were offered one type of folia ge in a no-choice situation, survival on young or mature leaves from glande d or glandless plants, with or without previous herbivore injury, did not d iffer significantly. However, pupae of larvae reared on young leaves of dam aged glanded cotton weighed significantly less than pupae from larvae fed a ll other diets. Pupae from larvae fed young leaves of control glandless pla nts weighed significantly more than pupae from all other diets. Similar tre nds were observed in adult weights. In addition, time to pupation and time to adult emergence were significantly longer for larvae fed young leaves fr om damaged glanded plants compared to all other diets. The experiments repo rted here link larval feeding behavior of S. exigua to performance. Larval feeding preferences changed following induction of systemic defense such th at food choice was optimized for growth.