Evaluation of laboratory-prepared water dispersible granules of Metarhizium rileyi (Farlow) Kepler, S.A. Rehner, and Humber against major soil pupating insect pests

Entomopathogenic fungi (EPF) exhibit formidable effectiveness that, under specific conditions, can offset the shortcomings of chemical insecticides within pest control programs. Among these EPFs, Metarhizium rileyi stands as one of the most extensively studied agents for global pest control. The study delves into the assessment of the relative virulence of M. rileyi water-dispersible granules (WDG) when deployed against distinct soil-pupating stages of lepidopteran and dipteran insects. M. rileyi WDG formulations were subjected to evaluation against various soil-pupating stages of insects, including lepidopteran and dipteran species. The results, based on dose-response relationships and LC50 values, revealed distinct levels of virulence exhibited by M. rileyi. Among the lepidopteran insects tested, M. rileyi demonstrated the highest level of virulence against H. armigera, followed by A. albistriga, A. flava, S. frugiperda, A. ipsilon, S. litura, S. obliqua, and A. janata. The LC50 values of these treatments, arranged in ascending order, were 2.01 x 107, 7.17 x 107, 1.13 x 108, 1.41 x 108, 1.54 x 108, 3.35 x 108, 3.62 x 108, and 1.00 x 109, respectively. In contrast, M. rileyi exhibited the least virulence against S. exigua, with an LC50 value of 1.35 x 109. Notably, the efficacy of M. rileyi WDG formulations was significantly lower when targeting dipteran pupae compared to lepidopteran pupae. For B. cucurbitae and B. dorsalis, the LC50 values were 7.26 x 109 and 1.29 x 1010, respectively. M. rileyi WDG demonstrated remarkable virulence when tested against the pupae of H. armigera, marking the highest level of efficacy observed. In contrast, these WDG exhibited limited efficacy when targeting dipteran pupae, such as those of B. dorsalis and B. Cucurbitae.