Efficacy of insecticides for longtailed mealybug control

Abstract

Five insecticides, acephate (780 mg/litre), imidacloprid (50, 100 or 150 mg/litre) and three experimental "organic" insecticides, YR55 (1.2 g/litre), YR65 (1 ml/litre) and YR70 (3.6 g/litre) as well as water control were applied three times (7-12 days apart) to pot plants of Asplenium bulbiferum (hen and chicken fern) infested with longtailed mealybugs (Pseudococcus longispinus). After three applications, the water-treated plants had 82% of fronds infested and a mean of 37 mealybugs on the youngest infested frond. The industry standard insecticide, acephate, reduced the mealybug populations to zero, while YR65 and imidacloprid reduced the infestation to 1-4% fronds infested and mean of 0.5-2.5 mealybugs on the youngest infested frond. In these treatments only old fronds were infested. YR55 and YR70 gave poor control and young fronds were infested. INTRODUCTION Mealybugs are a serious pest of many home and garden plants. The white waxy insects and the associated sooty mould spoil the appearance of plants. These pests are difficult to control with a single insecticide application, because some mealybugs are concealed and not hit by contact sprays and concealed females often cease to feed when egg laying starts. These non-feeding females cannot be killed with systemic insecticides. Once adult mealybugs establish on plants, the plants can be invaded by crawlers (first instar nymphs) over many weeks. One strategy to control the pest is to prevent the establishment of young mealybugs, by applying insecticides several times until crawler production ceases. A greenhouse experiment was undertaken to test the efficacy of a new strategy of applying a cluster of three sprays of insecticides to reduce severe mealybug infestations when all life stages were present. The trial also examined the efficacy of new insecticides for use on ornamental plants in the home and garden. These insecticides, including three "organic" products and imidacloprid, were compared with an industry standard, acephate. Imidacloprid is a systemic insecticide with good activity against sucking insects (Anon. 1992) and it does not have the smell associated with commercial formulations of acephate.