Host-plant phenology and Colorado potato beetle (Coleoptera: Chrysomelidae) population trends in eastern Washington

Developmental phenology of host plants and population trends for Colorado potato beetle, Leptinotarsa decemlineata (Say), were studied in eastern Washington in 1993 and 1994. Volunteer potato emerged earlier than cultivated potato and served as the earliest food source for the beetle. Hairy nightshade, Solanum sarrachoides Sendtner, first appeared in mid-June, and continued to germinate throughout the season. Overwintered adult beetles moved >300 m to colonize cultivated potato in early spring before germination of nightshade. The number of 1st-generation eggs were highly correlated with the number of adults colonizing potato, indicating that population size of the Ist generation was determined largely by the density of colonizing beetles. Many Ist-generation adults moved off of potato and onto nightshade. These adults hardly moved >100 m if nightshade plants were available on the perimeter of or in the potato fields. Population densities of end-generation beetles were higher on nightshade than on potato. Our results indicate that management strategies should focus on controlling populations of the 1st generation by reducing densities of beetles colonizing potato.