Sperm Precedence in Overwintered Colorado Potato Beetle (Coleoptera: Chrysomelidae) and Its Implications for Insecticide Resistance Management

Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most important insect defoliator of potatoes and is infamous for its ability to develop insecticide resistance. Sperm precedence is an important consideration in developing resistance management plans. We determined the precedence of sperm from a postdiapause spring mating by using irradiated sterile males. We also investigated whether spring mating (with or without fertilization) affects reproduction of overwintered females. Precedence of sperm from spring matings versus overwintered sperm from fall matings was almost complete. Some fertilization from fall matings did take place in this experiment, but it exceeded 10% in only one of the 22 pairings. Females mated only the previous fall laid fewer eggs than spring-mated females, but spring mating did not seem to improve the hatch rate of deposited eggs. On average, mated females started laying 1.6 d sooner than fall-mated females, but this difference was not significant. Hatch rate did not change with time. Precedence of spring matings over stored sperm can help compensate for assortative summer mating among resistant individuals due to differences in developmental time between refuges and treated areas.