Abstract
We investigated the insecticidal activity of a trehalase inhibitor, validoxylamine A (VAA), against insecticide susceptible (S) and resistant (R) strains of the green peach aphid, Myzus persicae. Four methods, leaf dipping method, two methods to determine the systemic activity using plants with roots (root soaking) and without roots (stalk-tip soaking), and parafilm method, which allows the aphids to suck artificial diet solution containing VAA through the parafilm membrane, were adopted for the tests. Mortality of first instar nymphs 2 d after treatment by leaf dipping method with 100 ppm VAA was about 10% in both S and R strains. The stalk-tip soaking method, however, showed strong effects of 100% and 88.5% against S and R strains, respectively, at 100 ppm VAA. At 20 ppm VAA in the root soaking method, 57.4% (S) and 49.9% (R) of female adults were dead within 7 d. The production of nymphs by the treated female was strongly suppressed. By the parafilm method, 20 ppm VAA caused complete mortality in female adults within 5 d. These results suggest that concentrations of VAA at the sucking site of the aphid was lower than that around the root where treatment occurred. For practical usage of these chemicals as insecticides, chemical modification is needed to improve the systemic characteristics.
