Evaluating the Efficacy of Plant Extracts in Managing the Bruchid Beetle, Callosobruchus maculatus (Coleoptera: Bruchidae)

An estimated 2000 plant species have been employed for pest control worldwide. The use of these botanical derivatives is thought to be one of the most cost-effective and sustainable options for pest management in stored grain. The present study was designed to assess the efficacy of five plant extracts viz; <i>Nicotiana tabacum</i> L., <i>Nicotiana rustica</i> L., <i>Azadirachta indica</i> A. Juss., <i>Thuja orientalis</i> L., and <i>Melia azedarach</i> L. against <i>Callosobruchus maculatus</i> L. Plant species extracts were applied at six different concentrations, i.e., 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0% in four replications. The phytochemical analyses of ethanolic extracts of five plant species showed variable amounts of phytochemicals i.e., alkaloids, flavonoids, saponins, diterpenes, phytosterol, and phenols. Total phenolic and flavonoid compounds were also observed. The efficacy of <i>A. indica</i> was highest, characterized by the lowest infestation rate (16.65%), host seed weight loss (7.85%), mean oviposition (84.54), and adult emergence (58.40%). In contrast, <i>T. orientalis</i> was found to be the least effective against <i>C. maculatus</i>, with the highest infestation rate of 25.60%, host seed weight loss of 26.73%, mean oviposition of 117.17, and adult emergence rate of 82.01%. Probit analysis was performed by estimating LC₅₀ and LC₉₀. The toxicity percentages of <i>N. tabacum</i> (LC₅₀ = 0.69%, LC₉₀ = 14.59%), <i>N. rustica</i> (LC₅₀ = 0.98%, LC₉₀ = 22.06%), and <i>A. indica</i> (LC₅₀ = 1.09%, LC₉₀ = 68.52%) were notable in terms of the lower LC₅₀ and LC₉₀ values after the 96-h exposure period against <i>C. maculatus</i>. Repellency was assessed by using the area preference and filter paper method. The repellency of <i>C. maculatus</i> on plant extracts increased with the increasing dose and time, such that it was the highest after 48 h. Likewise, at a 3% concentration, <i>A. indica</i> demonstrated 100.00% (Class-V) repellency followed by <i>N. tabacum</i> (96.00%, Class-V), <i>N. rustica</i> (74%, Class-IV), <i>M. azedarach</i> (70.00%, Class-IV), and <i>T. orientalis</i> (68.00%, Class-IV). Based on the findings of this study, we recommend integrating <i>N. rustica</i>, <i>N. tabacum</i>, <i>A. indica</i>, and <i>M. azedarach</i> for effective management of <i>C. maculatus</i> and highlight the potential of these plant species in the formulation of new biocidal agents.