Decoupling Host Preference and Performance in Callosobruchus maculatus (Fabricius, 1775): Roles of Seed Biochemistry and Botanical Insecticides in Stored Legumes

Callosobruchus maculatus (Fabricius, 1775) is a major postharvest pest of stored legumes, causing significant quantitative and qualitative losses. This study evaluated host preference, biochemical determinants of susceptibility, and the insecticidal efficacy of plant powders and aqueous and ethanolic extracts against C. maculatus among selected pulse species. In free-choice assays, oviposition preference did not correspond with developmental success, as Phaseolus vulgaris Linnaeus, 1753, received the highest number of eggs but supported minimal adult emergence, whereas Vigna radiata (Linnaeus) A. Jussieu, 1954, exhibited the highest level of infestation and seed damage. Biochemical analysis revealed correlational patterns: higher carbohydrate and lipid contents were positively associated with infestation and seed weight loss, whereas fiber content showed a negative association with pest performance. Protein content was correlated with oviposition, while moisture and fiber were associated with reduced developmental success. Plant-derived treatments significantly affected all biological parameters of C. maculatus in a concentration- and time-dependent manner, with the exception of sex ratio. Among the tested botanicals, Azadirachta indica A. Jussieu (1830) consistently showed the highest toxicity, with the lowest LC50 values across exposure periods. Ethanolic extracts showed greater insecticidal activity than aqueous extracts, indicating solvent-dependent extraction of bioactive compounds. Mortality increased progressively with exposure duration, accompanied by decreasing LC50 values, suggesting cumulative toxic and developmental effects. Overall, the results demonstrate that host suitability is governed by the interaction between nutritional composition and structural seed traits, while botanical extracts, particularly those from A. indica, offer effective, eco-friendly alternatives for managing C. maculatus in stored legumes.