Author : Ouab Santhoy

Summary : Plant shake and direct observation sampling methods were equally reliable in sampling larval populations of Spodoptera litura Fabr., Chrysadeixis chalcites Esper., Heliothis armigera (Hubner) and Lamprosema indicata Fabr., but plant shake was more economical in terms of time required. The egg and larval populations were higher during the dry season than the wet season. Egg and larval population densities were positively correlated only during the dry season (r= 0.56) but negative during the wet season (r = -0.03), indicating higher percentage egg hatchability and more larval survival during the dry season than the wet season. Plant age and climatic conditions appeared to strongly influence oviposition and larval survival. Larval parasitization was minimal (4.4 percent dry season and 4.9 percent wet season) and no egg parasites were detected. The larvae parasites were recorded as an unidentified tachinid sp. (Tachinidae: Diptera); Microplitis sp. (Braconidae: Hymenoptera), and Enicospilus sp. (Ichneumonidae: Hymenoptera). H. armigera eggs appeared overdispersed, while larval populations tended to be random. The choice of oviposition sites depended on the plant growth stages. Moths preferred young leaves, mature green leaves, stem and petioles in descending order. From 52 to 76 days after crop emergence (DE) there was strong oviposition attraction to pods where more than 80 percent of eggs were found. The insecticide decamethrin (0.05 kg a.i./ha) at weekly application intervals from 7 to 76 DE, gave good protection against insect pest complex only during the dry season.