Field-collected populations of Aphytis holoxanthus DeBach (Hymenoptera: Aphelinidae) and of A. lingnanensis Compere were selected for malathion and azinphosmethyl resistance, respectively, utilizing the male selection method. In preliminary experiments, fertility of virgin females was not significantly lower than that of mated females, and the rate of development of their progeny was similar. Males proved more susceptible to pesticides than females, and among them the sons of virgins were more susceptible than the sons of mated females. Some after-effects of sublethal exposure to pesticides were noted in both species. A mating ratio of 1 selected male: 2.0-2.5 females was optimal. Cold storage of female pupae proved feasible for synchronizing availability.Resistance of A. holoxanthus to malathion was not increased by 25 male selection cycles. Resistance of A. lingnanensis to azinphosmethyl, which had already been improved by mass selection, was further increased by 7 cycles of male selection.The different outcomes of the two projects are discussed in relation to the variability of the original field populations, and the results of male selection are compared with those of mass selection of identical populations.
The economic threshold determinants for the Asian corn borer, Ostrinia furnacalis (Guenée) were defined over several croppings. The relations between leaf injury, larval equivalents and the corresponding yield losses were established. The larval equivalents did not necessarily follow the increase of the leaf injury rating during the late whorl stage. Leaf damage and the larval equivalents correlated well with yield loss. Using the number of larvae per plant as parameter based on current prices of corn and other inputs, an ETL of not more than one larva/plant was established. The egg mass density, larval population and egg mass frequency indices were positively correlated, especially at their respective peak densities. LIR or leaf damage, number of larvae per plant and the frequency index of egg masses were indicated as good determinants of the ETL, with the egg mass frequency as most practical and convenient for use by farmers.
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