title: The Characterization of Carbamate Resistance in the Colorado Potato Beetle, Leptinotarsa decemlineata (Say), in Comparison with the House Fly, Musca domestica (L)
Creators: name: Rose, Randy L.
Publisher: name: Utah State University
Year: 1982

description: Resistant and susceptible populations of the Colorado potato beetle, Leptinotarsa decemlineata (Say), and the house fly, Musca domestica (L), were compared with respect to carbofuran and carbaryl toxicity in the presence and absence of the synergist, piperonyl butoxide. Resistance levels of the New Jersey population when compared with the susceptible Logan population by topical application of carbaryl and carbofuran were > 833 and 820, respectively. A resistance level of 583 was determined from carbofuran bioassays of Rutgers and NAIDM house flies. Similar levels of resistance development between these species suggests the possibility that similar resistance mechanisms may be involved.
Utilization of the synergist difference approach for evaluating synergism of these carbamates by piperonyl butoxide indicated that the resistant strains depended to a much greater extent upon detoxication by monooxygenases than did their susceptible counterparts. While piperonyl butoxide synergism resulted in completely restoring the the Rutgers strain of house flies to levels of susceptible counterparts. While piperonyl butoxide synergism resulted in completely restoring the Rutgers strain of house flies to levels of susceptibility, New Jersey Colorado potato beetles were able to retain a significant portion of their resistance and to investigate the possibility that decreased absorption was responsible for the degree of resistance retained following piperonyl butoxide pretreatment.
Microsomal preparations from Colorado potato beetle gut and fats body were devoid of measurable monooxygenase activity as determined from O-demethylation of p-nitroanisole, in spite of attempts clear gut contents and optimize techniques. In contrast, microsomal preparations from Rutgers and NAIDM house flies demonstrated clear differences in oxidative potential between strains.
An analysis of the distribution of NAHPH-cytochrome c reductase in Colorado potato beetle microsomes revealed a loss of enzyme activity from the microsomal pellet into the soluble fraction. The solubilization of this component of the electron transport chain is suggested as a possible limiting factor for in vitro characterizations of the involvement of cytochrome P-450 in xenobiotic metabolism.
Determination of NADPH oxidation from microsomal preparations from house flies abdomens and Colorado potato beetle gut and fat body did not demonstrate quantitative differences between tissue sources nor populations of either species. In a similar manner, NADPH-cytochrome c reductase did not vary between house fly strains nor between tissue sources of Colorado potato beetle. There was, however, approximately a two-fold difference in NADPH-cytochrome c reductase activity between resistant and susceptible populations of Colorado potato beetle larvae.
The in vivo distribution of 1-naphthyl-N-methyl (14C) carbamate in resistant and susceptible Colorado potato beetle larvae demonstrated that although significant quantitative differences did not exist between populations with respect to the rate of penetration, excretion, of the radiocarbon was significantly greater in the resistant New Jersey population.
This study has been successful in establishing that monooxygenases play a chief role in Colorado potato beetle resistance to carbamate insecticides. This role in Colorado potato beetle resistance to carbamate insecticides. This role was confirmed in part by an increased rate of NADPH-cytochrome c reductase activity in the resistant population, however, traditional xenobiotic metabolism could not be confirmed by other methodology examined. This may be a result of the apparent solubilization of NADPH cytochrome P-450 reductase from microsmal preparations due to the unconfirmed presence of an endogenous inhibitor. Further characterizations of resistance mechanisms need to be examined for this destructive agricultural pest.