EFFECTS OF MICROCLIMATE AND PLANT CHARACTERISTICS ON THE DISTRIBUTION OF A WILLOW FLEA BEETLE, ALTICA-SUBPLICATA

Effects of microclimatic conditions (temperature, wind and relative humidity) and host plant characteristics (height, plant density and genetic resistance) on the local distribution pattern of a specialist insect herbivore, Altica subplicata, were studied on sand dunes on the shores of the Great Lakes in northern Michigan. Adult beetle densities and herbivore damage were highest on young host plants (Salix cordata and S. exigua), which were growing near the shore, and both beetle density and damage decreased with increasing distance from shore. Beetles were never found on the oldest, tallest plants farthest from the shore. Of the factors investigated, relative humidity explained the greatest amount of variance in beetle damage and distribution (21-27%), and plant height was also a significant factor. Altica subplicata caused significantly more damage and was more abundant in areas with higher relative humidities, and on taller plants within those areas. Beetles exhibited no preference in a choice experiment with clones from plants growing near shore vs. clones from plants growing far from shore; thus distribution patterns did not result from genetic differences between plants in resistance to beetles. Beetle distributions were also not influenced by temperature, wind or plant density.