Insecticidal potential of traditionally important plant, Zanthoxylum armatum DC (Rutaceae) against cabbage butterfly, Pieris brassicae (Linnaeus)

Abstract

Cabbage butterfly, <em>Pieris brassicae </em>(Linnaeus) is one of the most destructive pests of brassicaceous crops. <em>Zanthoxylum </em><em>armatum </em>DC (Rutaceae) is versatile, traditionally important and edible medicinal plant, known to have insect repellent and larvicidal properties against many pests. Thus, the insecticidal potential of <em>Z. armatum</em> was evaluated against <em>P. brassicae</em>. N-hexane fraction of different plant parts of<em> Z. armatum </em>was extracted by using standard Soxhlet extraction method. Median lethal concentrations and time (LC₅₀and LT₅₀) were determined by contact and oral toxicity tests by using Probit analysis. Pericarp and leaf extracts were found toxic to the caterpillars by contact. LC_50’s of pericarp and leaf extract (by contact) was found to be 0.15% and 0.22%, respectively at 72 h. The relative toxicity of pericarp extract was recorded to be 1.50, when Azadirachtin 0.15 EC was considered as a unit. With sub-lethal concentrations, the developmental time was delayed; while percentage of pupation and adult emergence was significantly affected in treated caterpillars. In semi-field study, egg-laying of the female butterfly was significantly reduced and larval mortality was considerably higher (up to 53.33%) within 72 h after treatment in plants treated with <em>Z. armatum</em> extracts. In field trial, significant reduction (67.92%) in larval population was observed within 5 days of spraying of <em>Z. armatum</em> extracts.