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 behavior, survival and development of larval beet armyworm, Spodoptera exigua Hubner (Lepidoptera: Noctuidae), on glanded and glandless `Stoneville 213' cotton, Gossypium hirsutum L. In a greenhouse study, neonate S. exigua placed on the terminal foliage of glanded cotton plants moved down the plant to feed on older leaves. The location of feeding was more concentrated towards the bottom of the plant on previously damaged plants than on undamaged control plants. In contrast, larval feeding on glandless plants was evenly distributed within the plant and no difference in distribution was noted on plants that had sustained previous herbivore injury when compared to undamaged plants. In a laboratory study, where larvae were offered one type of foliage in a no-choice situation, survival on young or mature leaves from glanded or glandless plants, with or without previous herbivore injury, did not differ significantly. However, pupae of larvae reared on young leaves of damaged glanded cotton weighed significantly less than pupae from larvae fed all other diets. Pupae from larvae fed young leaves of control glandless plants weighed significantly more than pupae from all other diets. Similar trends were observed in adult weights. In addition, time to pupation and time to adult emergence were significantly longer for larvae fed young leaves from damaged glanded plants compared to all other diets. The experiments reported here link larval feeding behavior of S. exigua to performance. Larval feeding preferences changed following induction of systemic defense such that food choice was optimized for growth.