Bioefficacy of Garlic, Allium sativum and Tobacco Nicotiana tabacum on Mortality, Ovipository Inhibition and Adult Emergence of the Cowpea Beetle Callosobruchus maculatus (Fab.) on Cowpea Vigna unguiculata (L.) (Walp.)

Abstract

Aims: To evaluate the efficacy of aqueous and ethanolic extracts of garlic and tobacco in the management of the cowpea beetle (Callosobruchus maculatus) and how these affect oviposition by adult females, adult emergence and sex ratio. Study Design: The study was conducted in a randomised complete block design consisting of six treatments and three replications. Place and Duration of Study: The experiment was carried out at the Biocontrol Section of Crops Research Institute, Kwadaso, Kumasi over a four month period. Methodology: Aqueous and ethanolic extracts of garlic and tobacco leaves were prepared; these preparations were compared with a standard chemical insecticide, Betallic and a control. Four kilogrammes of untreated cowpea seeds were sorted to obtain whole uninfested grains. Six hundred of the sorted seeds were placed in 1L Kilner jars. Fifty millilitres of each extract was sprayed onto the seeds in their respective jars and allowed to dry. Ten pairs of adult C. maculatus were introduced into each jar. Similar set-ups were done with the insecticide and control seeds. Mortality was recorded every 6 hours after treatment for 24 hours. Data were also collected on oviposition, adult emergence and sex ratio. Results: Garlic-treated seeds did not record any mortality within the first 18 hours; no mortality was recorded in the control seeds, whereas the insecticide-treated seeds recorded 100 % mortality. Significantly fewer eggs were laid on the treated seeds than the control seeds. Sex ratio of the emerged adults varied within the period of observation. Aqueous extracts of the botanicals performed better in terms of insect control and oviposition inhibition than the ethanolic extracts. Conclusion: Aqueous extracts of both plants produced better results than the ethanolic extracts. Aqueous extract, being cheaper, easier and safer to prepare could be adopted by the average small-scale farmer to manage C. maculatus.