LABORATORY EVALUATION OF FIVE INDIGENOUS PLANT EXTRACTS AGAINST Callosobruchus chinensis L. (COLEOPTERA: BRUCHIDAE)

Abstract

Pulse is one of the best sources of a protein and plays a pivotal role in the diet of common people of Bangladesh. Among the storage insect pests, bruchids are known to cause both quantitative and qualitative losses to pulses. Among them, Callosobruchus chinensis L. (Coleoptera: Bruchidae) is a major and destructive species that causes up to 100% lossess of pulses in storage. The experiments were conducted to evaluate the bio-efficacy of five indigenous plant extracts in acetone solvent with three concentrations along with a control (0, 1.5, 2.5, 3.5 mg/ml) for direct toxicity, repellency and residual effects against pulse beetle, in laboratory conditions (28 ± 5°C, and 75 ± 10% RH). Direct toxicity and repellency tests were done using the residual film method of Busvine (1971) and according to the method of Talukder and Howse (1994a), respectively. Residual toxicity was conducted using gram seed mixed with each concentration. All the tested extracts had toxic, repellency and residual effects in controlling the beetle. However, the neem extract had the highest toxicity. All the data related to morality, repellency and residual effects showed statistical difference (P<0.05) among the extracts and their doses used. The neem extract exerted the highest adult mortality (mean mortality 35.0%) while the mahagony extract showed the lowest value (mean mortality 20.6%). The lowest LD50 values of neem extracts were 9.88, 2.50 and 1.59 mg/cm2 at 24, 48 and 72 HATs, respectively which proved the highest toxicity of the neem extract. The order of the toxicity of the five plant extracts were as neem >akanda> ghoraneem> gada> mahagony. The mortality was directly proportional to the period of treatments which increased with the progress of time. The neem extract also showed the highest repellency (89.8%) belonging to the repellency class V but mahagony extract had the lowest value (41.3%) possessing the repellency class III. Oppositely, the highest residual toxicity was in the neem extract while the least effect was in the mahagony extract. The findings of the current study would be very effective for ecofriendly management of the pulse beetle in storage.