Evaluation of a native isolate of Metarhizium anisopliae (Metschn.) Sorokin TMBMA1 against tea mosquito bug, Helopeltis theivora infesting cocoa (Theobroma cacao L.)

Abstract

The tea mosquito bug, Helopeltis spp. is a destructive pest of cocoa across the globe. In the climate change scenario, the tea mosquito bug species complex, viz. Helopeltis theivora Waterhouse, 1886, H. bradyi Waterhouse, 1886, and H. antonii V. Signoret, 1858, poses a serious threat to cocoa cultivation in India. Presently, systemic and/or broad-spectrum insecticides are used for mirid management by cocoa growers. However, concerns about their adverse effects on human health and the environment prompted us to search for alternative eco-friendly options for their management. Entomopathogenic fungi (EPF) are an effective and eco-friendly alternative to chemical insecticides for the management of cocoa mirids. The use of native strains of biological control agents improves their success rate. Hence, the present investigation was conducted to isolate, characterize and evaluate an indigenous insect-pathogenic isolate of EPF Metarhizium anisopliae against the mirid H. theivora. An extensive survey was conducted in the Dakshina Kannada district of Karnataka, India, to collect the adults of H. theivora naturally infected with entomopathogenic fungi. A pure culture of the EPF named as TMBMA1 was isolated from the infected adults. Based on the detailed morphological and molecular characterization, the isolate TMBMA1 was identified as Metarhizium anisopliae (Metsch.) Sorokin. The isolate TMBMA1 was found to be highly effective against H. theivora in an in-vitro bioassay and caused 100% insect mortality at 1 × 108 and 1 × 109 conidial suspensions 6 days post inoculation. Similarly, TMBMA1 was found effective in significantly reducing the incidence of mirids in field evaluations conducted for two consecutive years. TMBMA1 was found better than other commercial biopesticides and was comparable with the recommended chemical insecticide Lambda-cyhalothrin. In conclusion, our results reveal that the native EPF, M. anisopliae isolate TMBMA1 has great potential against the mirid H. theivora and can serve as an eco-friendly and sustainable alternative for mirid management in cocoa and other plantations in India.