Coevolution of the Life History of a Tropical Seed‐Feeding Insect and its Food Plants

Abstract

Field and laboratory studies of Dysdercus bimaculatus (Pyrrhocoridae; Heteroptera) were conducted in Costa Rica and Panama. The purpose of this work was to relate the life history of this insect and its host plants to the broader evolutionary context of the Dysdercus—Malvales association. Nymphs and adults feed on seeds of four tree species: Sterculia apetala (Sterculiaceae), Ceiba pentandra, Pseudobombax septinatum, and Bombacopsis quinata (Bombacaceae). The distance between trees and the hystolysis of wing muscles upon oogenesis effectively limit all the offspring of a female to one seed crop. These crops mature at different times during the tropical dry season. Crops are usually short lived and seeds are highly oleganious. Thus, the host plants of D. bimaculatus create a course—grained patter of point concentrations of energy—rich food resources occurring unpredictably in time and space. Migration and diapause are important "options" in the life history of the adult. Evidence that adult D. bimaculatus do fly between seed crops is indirect. Adult insects first appeared in the ripening fruits of the crops of one species after fifth—instar nymphs first occurred in the samples at the earlier ripening species. In the laboratory, females tended to delay egg development when food was plentiful but water limited. In the field, a declining proportion of nymphs appeared to remain and reproduce as adults at an usually long—lived S. apetala crop as conditions became drier. I proposed that uncertainty in the location in time and space and the level of moisture stress at different crops would account for variability in the tendency of females to develop eggs when water was limited. Two evolutionary processes would account for the association of D. bimaculatus with its particular type of food plants, relative to the many types of plant forms, seeds, and fruiting schedules in the Malvales: (1) I proposed that energy—rich food resources are required for D. bimaculatus to grow to its large adult size. Large body size is, in turn, though to enhance survival during diapause, migratory capacity, and reproductive output of this species. At present, these relationships are inferred from ecologically similar species. (2) I assumed that the risk associated with diapause is a function of time. This leads to the conclusion that D. bimaculatus populations would be dominated by individuals which included in their range all Malvales that produced concentrations of energy—rich seeds.