Kazam Ali - Centre for Agriculture and Bioscience International, Central and West Asia, Rawalpindi, Pakistan.
Muhammad Sagheer - Department of Entomology, University of Agriculture, Faisalabad, Pakistan.
Mansoor ul Hasan - Department of Entomology, University of Agriculture, Faisalabad, Pakistan.
Abdul Rashid - Department of Plant Pathology, University of Agriculture, Faisalabad, Pakistan.
Muhammad Shahid - Department of Bio-Chemistry, University of Agriculture, Faisalabad, Pakistan.

The present research was performed to evaluate the bioactivity of Citrullus colocynthis (L.) and Melia azedarach L. extracts against three major stored grain insect pests including Tribolium castaneum (Herbst), Trogoderma granarium Everts, and Sitophilus granaries (L.). Toxicity and enzyme inhibition activity of acetylcholinesterase (AChE), α-carboxylesterase (α-CE), β-carboxylesterase (β-CE), acid phosphatases (ACP) and alkaline phosphatases (ALP) in three insect species induced by both plant extracts were evaluated at four different dose rates viz., ۵, ۱۰, ۱۵ and ۲۰%. Results showed maximum mortality (۳۴.۲۹%) in S. granarius with M. azedarach at maximum interaction of time and dilution level. In T. castaneum and T. granarium maximum recorded values for mortality were ۳۰.۸۷% and ۱۸.۹۵%, respectively, with extract of M. azedarach. Plant extract of C. colocynthis reported a maximum mortality of ۲۱.۹۲%, ۱۹.۱۸% and ۱۶.۸۹% in T. castaneum, S. granarius and T. granarium, respectively. Findings proved that both plant extracts had decent lethal impacts on tested insect species. Exposure of studied insects to plants extracts also resulted in significant inhibition of AChE, α-CE, β-CE, ACP and ALP. All tested enzymes in three insects were maximally inhibited by plant extract of M. azedarach except α-CE which was slightly more inhibited in S. granarius and ACP which was highly inhibited in T. granarium and S. granarius, by plant extract of C. colocynthis. Outcomes exhibit that plant based extract of M. azedarach is more pronounced in stored grain insect pests and propose the capability of using these plant extracts for safety of stored commodities as a safe substitute for insecticides.

stored product pests, enzyme inhibition, lethal effects, toxicity