ASPECTS OF THE ECOLOGY OF THE TWOSPOTTED SPIDER MITE IN NORTHEASTERN NORTH CAROLINA

These studies were conducted to gain biological and ecological information on the twospotted spider mite that could eventually lead to the development of a successful pest management program.; Two closely related species, Tetranychus urticae Koch and T. cinnabarinus (Boisduval), are found in the study area (Chowan County, N.C.). Differences in the density of dorsal integumentary lobes of the two species were studied using the scanning electron microscope. The number of lobes per 10 microns along a single integumentary fold averaged 6.44 (S.E. = .85, n = 30) for T. urticae and 7.47 (S.E. = .81, n = 30) for T. cinnabarinus.; The effects of selected pesticides on natural enemies of T. urticae and the subsequent response of the spider mite populations was studied. The fungicide benomyl resulted in reduced infection of the mites by the pathogenic fungus, Entomophothora floridana, while fentin hydroxide had no effect on the fungus. Foliar applications of the insecticides carbaryl and methomyl reduced predator populations, but these reductions were not necessarily correlated with increases in T. urticae populations. Carbaryl stimulated oviposition by T. urticae and methomyl had a suppressant effect on populations of the mite.; The twospotted spider mite was observed overwintering on feral host plants during the winter months. Colonies of mites collected in the winter were actively reproducing.; The pathogenic fungus E. floridana, was found overwintering in the carcasses of dead mites as unsporulated conidia. Laboratory studies found that sporulation, infection and development of the pathogen occurred at temperatures commonly observed during eastern North Carolina winters.; Abrupt declines of spider mite populations in corn were associated with a high incidence of E. floridana. Elimination of this pathogen did not prevent these declines, which were apparently due to a decline in the suitability of the senescing corn plants as a host for the mites. A period of ca. 40 h of unusually high humidity and cool temperatures occurred each year ca. 2 weeks prior to an identifiable increase in the incidence of the fungal pathogen. About 3% of the mites dispersing on wind currents were infected by the fungal pathogen and thus carried the disease to new sites.; A study of the inter-crop relationship between corn and peanuts revealed that corn acts as a nursery crop for spider mites. As the corn plants senesced, the mites dispersed with the wind. Aerial trapping and the labelling of mites verified this planktonic dispersal from corn to new host sites including peanuts.