Insect Life Histories in Relation to Migration, Body Size, and Host Plant Array: A Comparative Study of Dysdercus

Abstract

The Dysdercus-Malvales insect-host plant association illustrates the relationship between body size, migration-colonization life histories and resource pattern. Trees in the order Malvales produce crops of large, short-lived concentrations of oil-rich seeds which are far apart in space and time. The largest species of Dysdercus in Africa and America are both specialist migrant colonizers of these arboreal resources. Large body size confers an advantage when resources are temporary because it allows increased rate of egg output and increased the chances of surviving long periods of migration and diapause. Within and between 9 spp. of Dysdercus [Dysdercus bimaculatus, D. suturellus, D. mimus, D. andreae, D. mimulus, D. fasciatus, D. nigrofasciatus, D. superstitiosus, D. cardinalis], larger females produce more eggs per clutch, and at a faster rate, than small females. Larger species produce larger eggs. The trend in the Malvales is for shrubs and annuals bearing seeds with lower oil content to be more evenly distributed than trees. Intermediate-size species of Dysdercus are generalist migrant colonizers with a wide array of seeds from trees and shrubs in the diet. These insects need not fly as far nor wait as long between seed crops as the arboreal specialists, but explosive reproduction is still an advantage. Ths smallest species has a non-colonizing life history, reproducting on the seeds of herbaceous weedy annuals. Females of this species spread the risk of individual mortality by minimizing egg volume and scattering egg clutches across low density resources. The body size and life history of species of Dysdercus are not only shaped by the resource pattern; they also limit the array of acceptable host plants. The large species are restricted to arboreal resources by the requirement for oil-rich seeds in order to grow large, and will not break diapause until food is in sufficient quantity.