Egg Parasitoids of Cabbage Caterpillars in Sri Lanka: A Search for Biocontrol Agents

Abstract

Purpose : Management of cabbage caterpillar complex through augmentative release of egg parasitoids has been suggested considering the current issues in insecticide application, mainly the effect on human health, non-target effects and environmental pollution. Use of local egg parasitoid species is preferred considering the environmental risk associated with the use of exotic species; therefore, this study was conducted to examine the egg parasitoid guild of cabbage caterpillars in Sri Lanka. Research Method : Field survey was conducted during January 2012 to May 2013 in major cabbage growing areas in the mid-country. Eggs of cabbage caterpillars were collected and reared them until the emergence of host larvae or adult parasitoids. Emerged parasitoids were preserved in 70% ethanol, and prepared the microscopic slides upon the dissection of male genitalia. Parasitoids were identified by using taxonomic keys and Trichogramma literature as per the protocol suggested by Natural History museum, London and the identities were confirmed by the taxonomist in Natural history museum in London. Findings : Trichoplusia ni, Spodoptera litura, Crocidolomia pavonana and Plutella xylostella were found as the members of cabbage caterpillar complex. Two egg parasitoid species: Trichogramma chilonis Ishi and Trichogramma achaeae Nagaraja and Nagarkatti were found attacking eggs of cabbage caterpillars. Trichogramma chilonis has been reported previously in Sri Lanka but Trichogramma achaeae is the first country report. T. chilonis was widely distributed and caused for higher level of parasitism than T. achaeae. The highest level of parasitism (67%) by both species was found in Trichoplusia ni eggs which was significantly different from other species. Level of parasitism of caterpillar eggs was significantly varied between pesticide free fields (16.8%) and conventional fields (13.1%). Research Limitation : The study of behavioral characters of these parasitoids is required to assess the suitability as biocontrol agents; as an initial step for augmentative biocontrol, the locally available egg parasitoids were reported in this study. Originality/ Value : These findings would be contributing Sri Lankan agriculture sector to develop the augmentative biocontrol approach to manage the cabbage caterpillar complex and to produce pesticide residues free crop produce.