Effect of gamma irradiation on proteases activities in Musca domestica.

Abstract

The treatment of foodstuffs with relatively low doses of gamma(y)-irradiation to reduce infestation by stored product insect pests has become increasingly widespread in many countries (1). In attempting to determine optimum yirradiation dosages to effect the above where insecticideresistant and susceptible individuals may be present in a population, the question arises as to how susceptibility to yirradiation between insects of different species andor insecticide-resistant and susceptible strains may be biochemically determined; in particular whether this susceptibility may be mediated by proteolytic enzymes, which are responsible for intracellular protein catabolism in all cells. The rational for this hypothesis is as follows (a) previous work has shown a link between y-irradiation and insecticide susceptibility in the flour beetle (Tribolium castaneum), although biochemical mechanism was not elucidated (2); (b) Substantially increased activity levels for a range of protease types in a pesticide resistant strain ofM. domestica, compared to susceptible (3); (c) y-irradiation of mammalian tissue extracts in vitro resulted in reduced activities for a number of protease types (4). In order to hrther elucidate this hypothesis effect of the yirradiation on the biochemical changes in organisms, the objective of present work was therefore to compare changes in protease activities in insecticide resistant and susceptible strains of M. dornestica following y-irradiation. A DDT resistant (17bb) and a susceptible (Cooper) strains of M. domestica were selected for investigation. Insects (approx. 25) in nutrient impregnated containers were subjected to yirradiation for 3 hrs (equivalent to 300 k Radd3 k Gray). This irradiation dosage was chosen to fall within the range ( m a 10 k Gray) normally used for irradiation for insect disinfection Samples of resistant and susceptible insects were placed in identical containers for 3 hrs, but not irradiated. AAer irradiation, insects were immediately frozen and stored at 40°C. After thawing insects were homogenized and proteolytic enzymes assays were carried out as described previously (5). The activity levels of cytoplasmic and lysosomal proteases in insects of resistant and susceptible strains following exposure to y-irradiation is shown in Table 1 For both the DDT resistant and susceptible strains of M. domestrcu, it is apparent that there was no significant difference in activity levels for any of the cytoplasmic and lysosomal proteases between irradiated and non-irradiated insects (note the increased levels of protease activity in 17bb strain compared to Cooper, as reported previously (3). We conclude from the above data (a) there is no difference in susceptibility to inactivation by y-irradiation for any protease type in 17bb and Cooper strains of M. domesticu; (b) there is no evidence for a difference in susceptibility to irradiation between DDT resistant and susceptible strains. Table I Protease actlvltles in 17bb and Coooer Stram of M donit!st~ca L following r i d a t i o n