Comparative Assessment of Insecticidal Effect of Azadirachta indica, Hyptis suaveolens and Ocimum gratissimum on Sitophilus zeamais and Callosobruchus maculatus
The powders of the leaves of Hyptis suaveolens, Azadirachta indica and Ocimum gratissimum were evaluated for comparative effectiveness in controlling Sitophilus zeamais Mots infesting stored maize grain (Zea mays) and Callosobruchus maculatus Fab infesting stored cowpea seeds (Vigna unguiculata). The powders were tested at 1.5, 2.5 and 3.5/80 g of the respective food materials. The parameters compared were adult mortality rate and emergence. The three plants tested showed more adult mortality and adult emergence of C. maculatus, where percentage adult mortality ranged from 83.3 to 93.4% for A. indica; 86.7 to 90.0% for O. gratissimum; 93.4 to 96.6% for H. suaveolens while S. zeamais recorded 13.3 to 50% for A. indica; 26.7 to 50% for O. gratissimum and 13.3 to 30% for H. suaveolens with the powders. The controls showed 0 to 33.4% mortality for C. maculatus compared with 0 to 3.3% obtained in S. zeamais within the same period. After 42 days post treatment adult emergence indicated that more C. maculatus ranging from mean number of 13 to 68 emerged while S. zeamais recorded 11 to 37 within the same period of consideration. The statistical analysis indicated that where significant differences occurred, it was caused by plant type other than concentration. The performance of individual plant type revealed that O. gratissimum and A. indica were better against S. zeamais than H. suaveolens where they caused mortality ranging from 13.3 to 50% with H. suaveolens recording 13.3 to 30.0%. However, the mortality ability of H. suaveolens against C. maculatus was better with a mean percentage mortality range of 93.3 to 96.6% compared with 83.3 to 90.0% caused by O. gratissimum and A. indica. The general emergence trend also indicated that H. suaveolens performed better in reducing emergence of new adults. These suggest that botanical insecticides are promising and their effectiveness varies with species.
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