POPULATION-DYNAMICS OF WHITEFRINGED BEETLE (COLEOPTERA, CURCULIONIDAE) ON SWEET-POTATO IN ALABAMA

Field sampling in sweet potato, Impomoea batatas (L.) Lamarck, was don e in 1992 and 1993 to elucidate the seasonal development of whitefring ed beetle, Naupactus spp., in sweet potato and the temporal occurrence of larval feeding damage to sweet potato roots. N. peregrinus (Buchan an) and N. leucoloma (Boheman) were the 2 whitefringed beetle species collected in adult samples; N. peregrinus was the predominant species in both years. Adult counts began to increase at the end of July with peak numbers in mid-to late August. Adult numbers declined below 1 per sample in mid-to late September to coincide with the onset of fall te mperatures and day length. A significant positive, linear relationship was established between adult counts and foliar feeding damage during the first 4-6 wk of sampling. Results of soil core sampling in 1993 i ndicated low survival of overwintered larvae in the soil with an incre ase in numbers of 1st-3rd instars in early August coincident with an i ncreasing adult population. The Ist larval feeding damage on sweet pot ato roots occurred in September when numbers of 4th-7th instars were i ncreasing. This was evidence that larvae hatching from eggs laid in ea rly or late summer reach sufficient size to damage sweet potato roots before fall harvest. Most feeding damage occurred on roots with a diam eter >4.5 cm, and damage continued through final harvest. These result s offer a possible explanation for the reported failures of pre-or at- planting applications of soil insecticides to control whitefringed bee tle damage. Alternative methods for management of whitefringed beetle in sweet potato are discussed.