Efficacy of vegetable oils against dry bean beetles Acanthoscelides obtectus.

Abstract

Acanthoscelides obtectus (Say) is a major pest of stored dry beans (Phaseolus vulgaris L.) and other legumes world wide. The objective of this study was to assess the efficacy of castor (Ricinus communis L.) and cottonseed (Gossypium hirsutum) oils against A. obtectus on stored dry beans under laboratory conditions. Castor and cottonseed oils at 0, 3, 4.5, 6, 7.5 and 9 ml kg^-1 were tested against A. obtectus. All bioassays were conducted at 28 ± 1 °C and 65 ± 5% relative humidity, and mortality recorded after 24, 48, 72, 96 and 120 hr of exposure. After the 120 hr mortality count, all the adults were removed and the vials were maintained at the same conditions for 35 days to assess progeny production. Mortality of A. obtectus significantly (P<0.05) increased with increase in dose of oil treatments and exposure interval. After 120 hr of exposure, mortalities were 99.1 and 74.1% at the highest dose (9 ml kg^-1) with castor oil and cottonseed oil, respectively. The lowest LC₅₀ value of 2.95 ml kg^-1 and complete suppression in progeny production were achieved on beans treated with castor oil at 9 ml kg^-1. However, in all treatments, the percentage of progeny reduction was more than 80%. In conclusion, results indicate that vegetable oils have great potential for A. obtectus control.

Key Words: Cameroon, castor, cotton, Phaseolus vulgaris, progeny reduction