Insecticidal Activty of Nishinda (Vitex Negundo) on Red Flour Beetle, Tribolium Castaneum (Hbst.)

Abstract

Insecticidal properties of nishinda (Vitex negundo L, family Verbinaceae) on red flour beetle (Tribolium castaneum Hbst.) was investigated. Bioactive compounds having pesticidal activities from nishinda leaves were isolated and identified. Other biological activities such as antimicrobial and brine shrimp bioassays were also elucidated with the isolated pure compounds. Nishinda leaves, stem barks and roots were sequentialiy extracted with organic solvents Pet spl, EtOAc, acetone and MeOH. Efficacy of these extracts was detennined against adult and different larval instars of three strains of T. castaneum usin_g residual film method. The contact toxicity on the test insect in tenns of LD50 (median lethal dose) of the extracts in different solvents from leaves, stem barks and roots were not similar. In general leaf extracts showed higher degree of toxicity on both larval and adult insects because, the LDso values for leaf extracts were lower than those recorded for stem bark and root extracts. The degree of toxicity in the order was leaves > stem barks > roots. The susceptibility of adult insects and larval instars to contact toxicity was different. The LD50 values for first through fourth instar larvae were more or less similar whereas. LD50 for fifth instar larva and adults were the lowest. Toxic effect on T. castaneum was also varied with the types and nature of organic solvents used for extraction. Among the solvents, methanolic extracts of all three-plant parts elucidated more toxicity on both adult and larval insects. The degree of toxicity according to solvents was MeOH > Pet spt. >acetone> EtOAc. Toxic effect of nishinda extract also varied with T. castaneum strains. Among the strains, FSS-II showed the highest degree of susceptibility to all types of extracts studied. The susceptibility order according to insect strains was FSS-II > CTC-12 > KANO.