The effects of larval population density and food quality on the velvetbean caterpillar, Anticarsia gemmatalis Hübner, were compared with investigations of other migratory noctuids. Crowded larvae of the velvetbean caterpillar responded with: (1) an increase in the degree of dark pigmentation; (2) a decrease in larval, pupal and adult size; (3) a prolongation of the larval stage and a decrease in weight gain in the ultimate stadium; and (4) low juvenile hormone and juvenile hormone esterase haemolymph titres.
The effects of flight, throughout a 4 hr flight period, on the haemolymph titres and whole body contents of carbohydrate and lipid are presented for the velvetbean caterpillar and discussed relative to other noctuid moths. Total carbohydrate concentration decreased during the first 30–45 min of flight, and total fatty acid concentration increased during the first 30–60 min of flight, after which it declined and stabilized at preflight levels. Lipid reserves and the small amount of lipid depletion after long periods of flight indicated that velvetbean caterpillar adults are capable of making long distance movements in which lipid is the principal flight fuel.
Juvenile hormone regulated the effect of density on larval colour, size and growth rate. Applications of juvenile hormone to crowded larvae increased the proportion of the lighter (green), larger and faster developing phase. This hormone action suggests that the juvenile hormone titre of crowded larvae is lower than that of uncrowded larvae.
Genetic differentiation among populations of velvetbean caterpillars suggests that south-central United States populations originate from overwintering populations in Mexico or south Texas. A system has been developed, using pheromone-baited bucket-type traps, to investigate the population dynamics and migration of the velvetbean caterpillar in Louisiana and Texas.