HOST-PLANT PHENOLOGY AND COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) POPULATION TRENDS IN EASTERN WASHINGTON

Developmental phenology of host plants and population trends for Color ado potato beetle, Leptinotarsa decemlineata (Say), were studied in ea stern Washington in 1993 and 1994. Volunteer potato emerged earlier th an cultivated potato and served as the earliest food source for the be etle. Hairy nightshade, Solanum sarrachoides Sendtner, first appeared in mid-June, and continued to germinate throughout the season. Overwin tered adult beetles moved >300 m to colonize cultivated potato in earl y spring before germination of nightshade. The number of 1st-generatio n eggs were highly correlated with the number of adults colonizing pot ato, indicating that population size of the Ist generation was determi ned largely by the density of colonizing beetles. Many Ist-generation adults moved off of potato and onto nightshade. These adults hardly mo ved >100 m if nightshade plants were available on the perimeter of or in the potato fields. Population densities of end-generation beetles w ere higher on nightshade than on potato. Our results indicate that man agement strategies should focus on controlling populations of the 1st generation by reducing densities of beetles colonizing potato.