Corn Rootworm Cholinesterase Activity as Influenced by Species, Sex, Age, and Cold Storage12

Abstract

Cholinesterase (ChE) activity was determined for larval and adult whole body homogenates of the western corn rootworm (WCR), Diabrotica Virgifera LeConte, and the southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber. Significant differences (P<0.001) existed in enzyme activity levels between the species at the 3 stages of comparison (3rd-instars, adult females, and adult males). Third-instar WCR had considerably higher ChE specific activity levels than WCR adults and 2nd-instar WCR when expressed on an individual basis. Third-instar SCR had less specific activity than 3rd-intar WCR. Enzyme levels of 3rd-instar SCR were similar to those of adult SCR enzyme levels. In WCR, ChE activity differences between the sexes were minimized when dimorphism by weight was considered. ChE was not stable beyond one day when the supernatant was refrigerated at 8°C, whereas freezing the supernatant at −12°C for 8 weeks caused no significant change when compared to fresh material. Storage of the supernatant at −12°C for 24 weeks reduced ChE activity by 6%