Developmental changes in the patterns of feeding in fourth- and fifth-instar Helicoverpa armigera caterpillars

Data are presented for developmental changes in feeding behaviour within an d across the fourth and fifth stadium of Helicoverpa armigera (Lepidoptera, Noctuidae) caterpillars fed nutritionally homogeneous semi-synthetic foods . We recorded the microstructure of feeding over continuous 12-h periods on consecutive days throughout the two stadia, and in one experiment recorded continuously for 21 h. Larvae in the two stadia showed the same general pa ttern of macro-events in feeding, including a similar duration of post-ecdy sis fast, which was usually broken by consumption of the exuviae, and then a sustained period in which discrete meals on the experimental food were ta ken regularly. There were, however, some distinct differences in the patter ns of meal-taking both between stadia and across different one-third time s egments within stadia. Considering between-stadium differences, the proport ion of time spent feeding differed significantly only in the last segment o f the feeding period of the two stadia, with the value for the fourth-insta r larvae being substantially greater than for fifth-instar larvae. As regar ds within stadium changes, the proportion of time feeding increased from th e first to the second segment of both stadia. However, whereas the proporti on of time feeding increased from the second to the final segment of the fo urth stadium, it decreased across the same period in the fifth stadium. The se patterns of changes in the proportion of time feeding within and between stadia, and their behavioural mechanisms (combination of meal durations an d meal frequencies), can be explained only partially with reference to incr easing food requirements with development. Three areas are identified where further study might help elucidate the reasons for the observed developmen tal changes in the microstructure of feeding: allometric constraint, the dy namic links between ingestion and post-ingestive processing, and ecological factors such as predation.