Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Jerry B. Graves

Abstract

Studies were conducted to characterize insecticide resistance and to document aspects of the basic biology of the cotton aphid, Aphis gossypii Glover, that were related to recommendations for integrated pest management. Laboratory, greenhouse, and field techniques were employed in these investigations. Significant levels of resistance were demonstrated to four recommended insecticide classes. Resistance appeared more stable over time for the organophosphate insecticide (chlorpyrifos) than for the organochlorine (endosulfan) and pyrethroid (bifenthrin) insecticide tested. The organophosphate resistance ratio of a clonal line of the cotton aphid was significant, but relatively low. Carboxylesterases, as studied by spectrophotometric and electrophoretic techniques, appeared involved as a mechanism of organophosphate resistance. Stable organophosphate resistance caused no reproductive disadvantage in the cotton aphid. Total reproduction of susceptible and resistant aphids was not significantly different, but reproduction during the first two days of adult life was significantly higher for the resistant aphids. Carboxylesterases were further implicated as a mechanism of organophosphate insecticide resistance. High polyphagy of the cotton aphid in the Mid-South was documented, with collections from 24 non-cultivated hosts throughout the year. Movement of winged aphids into young cotton occurred gradually, rather than in a single major flight. Economic outbreaks in cotton occurred on approximately the same date for nine out of ten fields sampled, and the early-season use of foliar insecticides did not appear to be a factor in determining the timing of these outbreaks. Cotton aphid populations were significantly greater in the middle of the canopy when populations were most heavy. Epizootics caused by the fungus, Neozygites fresenii (Nowakowski), effectively regulated mid-season infestations, and its prevalence was significantly greater lower within the canopy. The braconid parasitoid, Lysiphlebus testaceipes (Cresson), also effectively regulated mid-season populations of the cotton aphid. The major aphid species occurring in cotton was A. gossypii, but several other species colonized cotton in early-season. These species did not occur at economic levels, however. The occurrence of the sexual phase (oviparae) of the cotton aphid was demonstrated in late-season cotton and on one non-cultivated host.

Pages

119

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