The Occurrence of Cholinesterase in Eggs of the Peach Tree Borer and Large Milkweed Bug and Its Relationship to the Ovicidal Action of Parathion1

Abstract

In eggs of Sanninoidea exitiosa and the large milkweed bug Oncopeltus fasciatus having incubation periods of 8.5 and 6.1 days, respectively (80o F), cholinesterase activity occurred about the 4th day and increased thereafter until hatching. The properties of esterases from the 2 spp. differed but the relationship of this fact to ovicidal susceptibility was not established. Striking contrast in susceptibility to ovicidal action was observed, the eggs of the peach tree borer being highly susceptible while those of the large milkweed bug were not affected by parathion at practical concns. In treated eggs of the peach tree borer cholinesterase inhibition occurred whether treatment was made before or after occurrence of the enzyme. In vivo inhibition was associated with ovicidal effectiveness while in vitro treatment caused over 50% inhibition in both susceptible and non-susceptible spp. Evidence tends to support the scheme previously advanced that the toxicant taken up at any stage remains in the egg-inhibiting cholinesterase when it appears; inhibition does not prove lethal until the late stages of embryonic development.