Microsomal Polysubstrate Monooxygenase Activity in Western and Mountain Pine Beetles (Coleoptera: Seolytidae)

Abstract

On the basis of polysubstrate monooxygenase (PSMO) activities in midgut tissue, we detected no difference in the biochemical breadth of diet of western pine beetles, Dendroctonus brevicomis Le Conte, and mountain pine beetles, D. ponderosae Hopkins. This result suggests that the number of taxa that these insects encounter may not be an accurate indicator of the diversity of toxins to which they are exposed. The biochemical diversity encountered by the host-restricted western pine beetle appears to be as great as that of the less host-restricted mountain pine beetle. PSMO activity of mountain pine beetles in their alternate host was significantly lower than that of mountain pine beetles in their preferred host; toxins in the alternate host may thus inhibit PSMO activity. Such inhibition may explain why, although mountain pine beetles colonize several different taxa throughout their geographic range, they prefer to colonize one taxon in any given locality and they shift to alternate hosts only rarely.