ABSTRACT
This study investigated and compared the protectant ability of powder and aqueous extract of tobacco and neem plants. This was done against the cowpea seed storage bruchid, Callosobruchus maculatus Fabricius under ambient temperature 29±30C, and relative humidity (r.h.) 65±5% in the laboratory.
Each treatment, including the control comprised three replicates which was laid in 2x4x5 factorial arrangement in a randomized complete block design. Ten males and fifteen females of teneral adult C. maculatus (0-24h old) were introduced separately into each of the petri dishes containing 20g cowpea seeds treated with leaf and seed powder at different dosage levels of 1.0g, 2.0g, 3.0g and 4.0g. Similarly, ten males and fifteen females of teneral adult C. maculatus (0-24h old) were introduced separately into the petri dishes containing 20g cowpea seeds each and treated with leaf and seed aqueous extract of tobacco and neem plant of 2.5%, 5.0%, 7.5% and 10.0% (vol. wt).
Results showed that powdered tobacco and neem plant parts evoked significant mortality (79.55%) of teneral adult C. maculatus after 7 days post treatment. Similarly, aqueous extract of tobacco and neem plant parts evoked significant mortality (79.67%) of teneral adult C. maculatus after 7 days post treatment. The result indicated that neem plant parts (powder and aqueous extract) were more effective in achieving mortality of adult bruchids (i.e. above 90% mortality). Also, all the treatments suppressed oviposition and adult emergence. Consequently, gave adequate protection by recording lower mean (54.23) in oviposition and (16.94) in adult emergence in cowpea seeds treated with powdered neem and tobacco plant parts. Similarly, lower means were recorded, 53.28 in oviposition and 17.15 in adult emergence in cowpea seeds treated with aqueous extracts of neem and tobacco plant parts. However, control recorded higher means in both oviposition and adult bruchid emergence. There was a general and appreciable reduction in means recorded in cowpea seeds treated with powdered neem and tobacco plant parts; 41.29 in damaged seeds: 0.04 in the development of bruchids, and 26.0 in weight loss. Likewise, cowpea seeds treated with aqueous extract of neem and tobacco plant parts gave lower means in damaged seeds, development of bruchids and weight loss. However, there was an increase in the recorded means of adult bruchid mortality (67.30) and undamaged seeds (105.78) in cowpea seeds treated with powdered neem and tobacco plant parts. Similarly, there was an increase in the recorded means of adult bruchid mortality (68.80) and undamaged seeds (99.54) in cowpea seeds treated with aqueous extracts of neem and tobacco plant parts compared with control. Therefore, all treatments had no adverse effect on cowpea seed quality as determined from viability test.
Among the treatments, higher concentrations of tobacco leaf powder and aqueous extracts were observed to be most effective as cowpea seed protectants in the complete inhibition of adult bruchid emergence. It was also the most effective treatment in reducing post-harvest weight loss.
However, powder and aqueous extracts of neem and tobacco plant parts were dosage-dependent as they were more effective at higher concentrations than at lower concentrations.
