Insect cytochromes P450: diversity, insecticide resistance and tolerance to plant toxins

In the last decade, studies of individual insect P450s have blossomed. This new information has furthered our understanding of P450 diversity, insecti cide resistance and tolerance to plant toxins. Insect P450s can be adult sp ecific, larval specific or life stage independent. Similarly, insect P450s vary as to the tissues where they are expressed and in their response to in ducers. Insect P450s can now be rapidly sequenced using degenerate PCR prim ers. Given the huge diversity represented by the Class Insecta, this techni que will provide vast amounts of new information about insect P450s and the evolution of the P450 gene superfamily. CYP6D1 is responsible for monooxyg enase-mediated resistance to pyrethroid insecticides in the house fly. CYP6 D1 is ubiquitously expressed in adults with 10-fold higher levels found in the resistant strain compared to susceptible strains. CYP6D1 is on autosome 1 in house fly. The high level of expression found in the resistant strain is due to genes on autosomes 1 and 2. Whether or not the different CYP6D1 alleles found in resistant and susceptible strains have any role in resista nce remains to be elucidated. The CYP6B gene subfamily is involved in the m etabolism of host plant toxins (i.e. furanocoumarins). CYP6B gene transcrip ts in two Papilio (swallowtail) species have been shown to be induced by ho st plant toxins and in turn to metabolize these toxins. CYP6B P450s play a critical role in allowing Papilio to adapt to furanocoumarin-containing hos t plants. Similarities in structural and promoter regions of the CYP6B gene s suggest that they are derived from a common ancestral gene. Although the P450 monooxygenases of insects are important for the metabolism of hormones and pheromones, no individual P450 has yet been shown to metabolize an end ogenous compound. Advances in this area are critical because they will prov ide important new information about insect physiology, biochemistry and dev elopment. (C) 1998 Elsevier Science Inc. All rights reserved.