Bioefficacy of plant essential oils against pulse beetlesCallosobruchusspp. (Coleoptera: Bruchidae) in pigeon pea seeds with particular reference toClausena pentaphylla(Roxb.) DC.

Thirty essential oils from higher plants of Gorakhpur Division (India) were evaluated at 0.36 μl/ml against two pulse beetles, Callosobruchus chinensis L. and C. maculatus F., causing infestation of pigeon pea seeds during storage. Clausena pentaphylla oil was more effective and exhibited absolute repellency against both the insects followed by Ocimum canum, Salvia plebeia and Zingiber zerumbet oils. Among these four oils, C. pentaphylla oil was most toxic and showed 100% mortality of both the insects at 10-μl dosage and 24-h exposure (LD50 = 2.7 μl for C. chinensis & 2.4 μl for C. maculatus). Physical factors, viz. temperature, storage and autoclaving, did not cause any adverse effect on the toxicity of Clausena oil. During in vivo investigation, the oil protected 1 kg of pigeon pea seeds completely without reducing weight loss and seed damage up to 6 months when stored in gunny bags and glass containers. The oil was standardised by determining its various physicochemical properties. Thus, C. pentaphylla oil can be judiciously exploited as herbal insecticide against pulse beetles of pigeon pea seeds during storage.