Efficacy of Neoseiulus longispinosus (Evans) (Mesostigmata: Phytoseiidae) for the Management of Tetranychus urticae Koch (Prostigmata: Tetranychidae) on Cucumber under Protected Cultivation

摘要

Cucumber is one of the most preferred crops grown in polyhouses of Kerala. However, incidence of spider mite, Tetranychus urticae Koch, 1836 as emerged as an important limiting factor for cucumber cultivation in the polyhouses. Increasing concern over the abuse of acaricides for mite management in polyhouses has necessitated development of alternative strategy with emphasis on biological control. The phytoseiid mite, Neoseiulus longispinosus (Evans, 1952) which has a wide distribution and has the ability to adapt to warm temperatures can be a potent candidate against tetranychid mites. To identify the optimum predator: prey ratio of N. longispinosus to T. urticae for effective management of spider mites, experiments were conducted both in the laboratory as well as polyhouse using a range of ratios. In the laboratory, the experiment was carried out on excised cucumber leaves maintained on moist sponge in plastic trays. Gravid females of N. longispinosus were released to 100 mixed stages including eggs, nymphal stages and adults of prey on cucumber leaves at predator: prey ratios of 1:5, 1:10, 1:20, 1:25, 1:33, 1:50 and 1:100. In the polyhouse, hundred mixed stages of T. urticae were released on four leaf stage of twenty days old cucumber plants at the rate of 25 mites/leaf, followed by the release of gravid females of N. longispinosus at predator: prey ratios of 1: 20, 1: 25, 1: 33 and 1:50. Laboratory studies showed that, at ratios of 1:5 and 1:10, the prey population was significantly reduced by third day. The prey was completely eliminated by seventh and tenth day at ratios 1:5 and 1:10 respectively. Ten days after the release, the prey population at ratios, 1 20, 1:25 and 1:33 were on par with that of 1:5 and 1:10. In the polyhouse, the predator: prey ratios of 1:20 and 1:25 were significantly superior in reducing the population of T. urticae on cucumber. The present study has revealed the potential of the predatory mite, N. longispinosus as a biocontrol agent against T. urticae on cucumber in polyhouse.