Scientific validation of plant extracts used by farmers in the management of bean flower thrips on French beans in Kenya

Summary in the original language of the document

Bean flower thrips (Megalurothrips usitatus ) is a major French bean (Phaseolus vulgarisL.) pest. Small-scale farmers manage the pest using mixed plant extracts althoughtheir efficacy has not been scientifically validated. We evaluated the efficacy ofmixed plant extracts comprising; Capsicum frutescens , Allium sativum , Lantana ca-mara , Tagetes minuta and Azadirachta indica , against M. usitatus under laboratory andscreenhouse. We identified and quantified the secondary metabolites associatedwith insecticidal activity using spectrophotometry and liquid chromatography–massspectrometry (LC–MS). The plant combinations included PE1 (C. frutescens + A. sati-vum + L. camara + T. minuta extracts infused for 14 days), PE2 (same as PE1 but infusedfor 24 h) and PE + N (the five plant extracts infused for 24 h) in distilled water. We usedan organic commercial botanical (Pyneem) as a positive control and distilled water as anegative control. Pyneem and PE + N induced the highest mortality at 88% and 77%,respectively, in the laboratory, and 68% and 71%, respectively, in the screenhouse.Phenolics, terpenoids and organosulfur compounds were identified in PE + N and indi-vidual plant extracts in varied quantities. These compounds were significantly higher(p < 0.001) in PE + N compared to individual plant extracts. The study showed thatPE + N efficiently manages bean flower thrips, and mixing different plant extracts am-plifies the secondary metabolites' abundance. The use of mixed plant extracts couldbe incorporated into integrated pest management strategies for thrips management in legumes. The specific compounds identified in PE + N should be investigated furtherto understand their modes of action against the pest.K