Entomopathogen-based biological control of looper pests (old looper, Biston (= Buzura) suppressaria and emerging looper, Hyposidra Talaca): an in vitro sustainable approach for tea pest management

Looper caterpillars including the Biston (= Buzura) suppressaria (Lepidoptera: Geometridae) and Hyposidra talaca (Lepidoptera: Geometridae), are recorded as major defoliating pests in tea [Camellia sinensis (L.) O. Kuntze], are responsible for a decline in tea bush quality, a decrease in yield, and extensive foliage deterioration. The hasty and unlawful usage of chemical pesticides for looper control has adverse effects, such as the deterioration of natural soil fertility, disturbance of beneficial plant-microbe interactions, and an elevated risk of pesticide resistance. Undesired pesticide residues are frequently detected in the final tea product as pesticides have been applied to eradicate looper caterpillars in tea crop. In the current investigation, spore suspensions of two entomopathogenic fungi, Beauveria bassiana (MG547581) and Metarhizium anisopliae (MG547580), have been employed in vitro to evaluate their effectiveness in controlling three distinct stages of the life cycle of looper caterpillar. The highest rates of microbial infection and pest mortality were measured in the prepupal stage of each pest during in vitro incubation studies and bioassay. Pest mortality up to 90% was recorded with a spore load of 3 × 10⁷ cfu/mL at the prepupal stage, while mortality in adults was up to 70% and influenced by species variations. The lowest median lethal dose (LD₅₀) values of M. anisopliae were recorded as 1.1 × 10⁶ (prepupae), 1.9 × 10⁶ (pupae) and 3.2 × 10⁶ (adult) against H. talaca and against B. suppressaria both the entomopathogens showed equal LD₅₀ values in all distinct stages like prepupae (5.3 × 10⁵), pupae (3.2 × 10⁶) and adult (7.6 × 10⁴). Further, median lethal time (LT₅₀) values increased gradually from prepupae, and pupae to adult, both in cases of H. talaca (3.69, 3.97 and 4.40 days in 3 × 10⁷ cfu/mL of M. anisopliae) and B. suppressaria (4.30, 4.72 and 5.34 days in 3 × 10⁷ cfu/mL of B. bassiana) due to entomopathogenesis. As eco-friendly and nonchemical options for tea looper caterpillar management appear to be limited, the current study explores putative microbial alternatives such as B. bassiana and M. anisopliae for the sustainable management of two significant defoliating pests of tea.