Population Dynamics of Whitefringed Beetle (Coleoptera: Curculionidae) on Sweet Potato in Alabama

Field sampling in sweet potato, Impomoea batatas (L.) Lamarck, was done in 1992 and 1993 to elucidate the seasonal development of whitefringed beetle, Naupactus spp., in sweet potato and the temporal occurrence of larval feeding damage to sweet potato roots. N. peregrinus (Buchanan) 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 temperatures 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 indicated low survival of overwintered larvae in the soil with an increase in numbers of 1st–3rd instars in early August coincident with an increasing adult population. The 1st larval feeding damage on sweet potato roots occurred in September when numbers of 4th–7th instars were increasing. This was evidence that larvae hatching from eggs laid in early or late summer reach sufficient size to damage sweet potato roots before fall harvest. Most feeding damage occurred on roots with a diameter >4.5 cm, and damage continued through final harvest. These results offer a possible explanation for the reported failures of pre- or at-planting applications of soil insecticides to control whitefringed beetle damage. Alternative methods for management of whitefringed beetle in sweet potato are discussed.