Seasonal prevalence of Hexamermis vishwakarma Dhiman (Nematoda: Mermithidae) parasitism in Leptocoris augur Fabr. (Heteroptera: Rhopalidae) infesting Schleichera oleosa in relation to environmental factors and its biocontrol potential

Hexamermis vishwakarma Dhiman, an entomophilic nematode, is thought to be a possible bio-control agent for Leptocoris augur , a pest of Schleichera oleosa . The nematodes develop inside the host insect through a number of nymphal and adult stages of L. augur prior to emerging from the host as fully developed, non-feeding postparasites. Host mortality results from the nematodes leaving the bug. The objective of this study was to identify the nematodes that parasitize L. augur and to chart (record) the level of parasitism in the population of L. augur in response to environmental factors like temperature and rainfall. The possibility for H. vishwakarma to exert biological control over the L. augur population through the occurrence of epizootics is discussed. The study was carried out in the HRI and Training Centre, which is situated in the Indian district of Saharanpur, from January to December and (Fortnightly from May to October). By comparing the number of H. vishwakarma Dhiman parasitized nymphs and adults bugs with the current rainfall and temperature at biweekly intervals, it was possible to determine the effect of abiotic conditions on the degree of parasitism in L. augur . In S. oleosa , there was a highly substantial positive association between the amount of parasitism and rainfall. From July to August, when there was the most rainfall in 2006, post-parasitic juvenile caused mortality in L. augur infesting S. oleosa was (81 and 88%, respectively), and the parasitism decreased as the amount of rainfall decreased. In the lab, the parasitization rate ranged from 80% to 100%. The percentage of parasitization in the bug population in the field was 10-88%. The majority of the bug population (80 to 90%) died in the cage within a month, which was a promising result for H. vishwakarma Dhiman. As a result, H. vishwakarma can be successfully used in India as an L. augur biocontrol agent. The inverse relationship between rainfall and H. vishwakarma Dhiman (mermithids) infection will be useful in planning when to apply pesticides in IPM plans to control this pest.