Evaluation of the effect of alkaloidal extracts of Duranta repens fruit on some biological parameters of cowpea beetle

Abstract

The present study aimed to evaluate the insecticidal efficacy of alkaloid extracts from Duranta repens fruits at concentrations of 4%, 6%, and 8% against different developmental stages of the southern cowpea beetle (Callosobruchus maculatus) under laboratory conditions. The tested stages included eggs, last instar larvae, and pupae at 24 and 120 h of age. The 8% alkaloid extract exhibited the highest ovicidal activity, achieving 100% egg mortality, compared to 60% mortality at the 4% concentration. Similarly, the 8% concentration induced the highest larval mortality (82%) in the last instar stage, significantly outperforming the lower concentrations. Pupae treated at 24 h old with the 8% extract recorded a 93% mortality rate, while 120-h-old pupae showed a reduced mortality rate of 77% at the same concentration. In contrast, the 4% extract resulted in 68% and 60% mortality for 24- and 120-h-old pupae, respectively. Furthermore, the 8% alkaloid extract was most effective in protecting stored cowpea seeds, recording the lowest seed loss (6.55%) after six months of storage, compared to the 4% and 6% treatments. The study also demonstrated that seed germination was not adversely affected by any treatment across all evaluation periods (1 day, 90 days, and 180 days). Overall, the 8% alkaloid extract of D. repens fruits proved to be the most effective concentration in controlling C. maculatus and preserving seed viability during storage.