Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

James A. Ottea


Biochemical and physiological mechanisms of profenofos resistance in laboratory and field populations of the tobacco budworm, Heliothis virescens (F.) were studied. High frequencies of profenofos resistance were recorded in all field-collected strains and were strongly correlated with esterase (EST) activity and moderately correlated with glutathione S-transferase activity. Mean levels of acetylcholinesterase (AChE) sensitivity to inhibition by chlorpyrifos oxon were lower in some field strains than levels in an insecticide-susceptible strain; however, AChE sensitivity and resistance were poorly correlated in all field strains. There was no correlation between resistance and the activities of P450-monooxygenase or glutathione S-transferase measured. Studies with laboratory-selected insects provided further evidence for the involvement of EST activity and AChE insensitivity in OP resistance. Activities of ESTs were higher in both laboratory-selected and field-collected larvae than that in the susceptible LSU strain. In electrophoretic gels, quantitative and qualitative variations were observed in banding patterns of ESTs toward $\alpha$ and $\beta$ naphthyl acetates. A unique band (designated as A$\sp\prime)$ was observed in all resistant larvae but none in the LSU individuals examined. The appearance of this band in resistant larvae coincided with decreased expression of a second band (designated as A). This pattern of overexpression of the A$\sp\prime$ band and underexpression of the A band also was observed in larvae collected from different sites. In a filter paper "squash assay", differences were observed in the intensity of color developed between susceptible and resistant strain insects, using individual, second stadium larvae. Further, insensitivity and decreased AChE activity were observed in laboratory-selected and field-collected larvae. Finally, inheritance studies suggest that resistance is polygenic and sex-linked in laboratory-resistant strains. In addition, LD$\sb{50}$ values for the parents and F1 progeny suggests that resistance was incompletely dominant in both crosses. However, inheritance of EST activity appeared to be incompletely recessive. Although mean levels of sensitivity of AChE were similar among the parental and F1 progeny of reciprocal crosses, differences in the inheritance of AChE activity suggest sex linkage.