Enzymatic responses in Oryzaephilus surinamensis (Coleoptera: Silvanidea) to plant extracts, entomopathogenic fungi and bacterial agents: Implications for pest control
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Abstract
Fluctuation in enzymes activity is an indicator of immune response to certain stress insect is observing. Oryzaephilus surinamensis, commonly known as sawtoothed grain beetle (STGB), is a devastating insect pest of stored products. Chemical-based management strategies for STGB are commonly used but have certain detrimental implication: residual effects on commodities, posing significant health risks, development of insect resistance. In this study, three different biocontrol treatments were evaluated for their virulence against STGB: plant extract (Brassica juncea), entomopathogenic fungus (Beauveria bassiana), and the entomopathogenic bacterium (Xenorhabdus nematophila). In the later part of current research shift in midgut enzymatic activity under these treatments has also been assessed. Results accentuated that corrected mortality percentage of STGB adults was significantly influenced by the bacterium, plant extract, and fungus. Entomopathogenic fungi, B. bassiana induced the highest mortality (66.7%), followed by X. nematophila (63.3%), while the lowest mortality in STGB was observed corresponding to B. juncea. The aforementioned treatments also inhibited a-amylase, lipase and protease activity in a time dependent fashion with peak α-amylase, protease activity on the third day after treatment, with significant declines in enzyme concentration by the fifth and seventh days. While, lipase activity remained almost constant on days 3 and 5, but a significant decline was detected on day 7 after treatment. The finding demonstrates that biocontrol tactics possess significant potential for managing stored insect pests, offering a economical and environmentally responsible substitute for chemical insecticides.
Keywords: Entomopathogenic fungus; Enzymatic activity; Insect pests of dates; Plant extract; stored product pest; Saw tooth beetle; Xenorhabdhus nematophila