Bio-efficacy of plant extracts against a major stored grain insect pest bruchid beetle F. Callosobruchus maculatus (Coleoptera: Bruchidae)

Abstract

A considerable portion of crops is lost due to the use of non-selective crop protection agents. Consequently, there is growing pressure on the agrochemical industry to develop new crop protection solutions that are both environmentally friendly and safe for consumers. The current study investigates the bio-efficacy of plant extracts (Melia azedarach L., Nicotiana rustica L., Azadirachta indica L., Nicotiana tabacum L., and Thuja orientalis L.) against Callosbruchus maculatus. The extracts of these plants were tested at six different concentrations (5, 10, 15, 20, 25, and 30%) using distilled water as a control. The experiments were replicated four times. Overall mean minimum oviposition (131.75), adult emergence (73.78%), infestations (28.14%) and host seed weight loss (12.54%) were observed with N. tabacum. Contact and residual methods were used to evaluate the toxic effects of the plant extract after 24-, 48-, 72- and 96-hours’ exposure period. The LC50 and LC90 values were determined by probit analysis. In case of residual toxicity, out of the five plant species extract, N. tabacum was the most toxic against C. maculatus with LC50 of 0.92% and LC90 of 4.77 % respectively. In contact toxicity N. tabacum was found effective against C. maculatus with LC50 of 0.14% and LC90 of 1.59% respectively. Alkaloids, saponins, di-terphenes, phyto-sterol, flavonoids and phenols were detected in the aqueous extracts of selected plant species. The current study highlights the efficacy of N. tabacum, N. rustica and A. indica for the management of C. maculatus. Further investigation is therefore necessary to evaluate the potential of these plant species for the production of new bio-pesticides as safer and eco-friendlier alternative to synthetic pesticides.