The temporal and spatial distribution of filbert weevil infested acorns in an oak woodland in Marin County

Abstract: Two-hundred shoots contained within randomly selected locations from each of thirty-six coast live oak, Quercus agrifolia, trees were sampled to determine the abundance and spatial distribution of acorns infested by the filbert weevil, Curculio occidentis in northern California during 1989. The seasonal abundance of infested acorns was highest at 30 percent during mid-September. Overall, 25 percent of all acorns ob-served on sample trees revealed signs of boring insect activity. Slightly higher infestation rate of 38 percent was obtained from laboratory dissections of field collected acorns (n = 501). Of those acorns dissected in the laboratory found to contain insect larvae, 70 percent contained C. occidentis and 30 percent con-tained the filbertworm, Melissopus latiferreanus. Although acorns were numerous on the sunny side of the tree, infested acorns were more abundant on the shady side. The differential distribution of acorns spatially within trees, acorn survivorship, and the impact of insect and other animal acorn predators on acorn production are discussed. The sweeping branches of a large regal oak is a vision common to all of us. As a single tree or forest stand, our native oaks play an important role in wildlife and human ecologies. In California there are 18 species of oaks, 10 of which reach tree size (Tucker 1980; Griffin and Muick 1990). The total acreage for California's oak species has been estimated at 15-20 million acres (Plumb and McDonald 1981). For thousands of years, native oaks have been a prominent and persistent floral feature in California. Unfortunately, it now appears many of our oak woodlands have been drastically reduced and are poorly regen