Species Composition, Biology and Management of Sweet Potato Weevils (Cylas Species) In Southern Ghana.
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Date
2000-09
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University of Ghana
Abstract
Species composition of sweet potato weevils (Cylas spp) on two sweet potato varieties was determined in the southern parts of the country. One species, Cylas puncticollis Boh. was found to be present in the southern part of Ghana. Studies on the biology of Cylas puncticollis were evaluated on two varieties, red and white varieties, under laboratory conditions at 27.0°C and 70% RH The incubation period of the eggs were 4 days on the red variety and 5 days on the white variety. Larval stages ranged from 10-11 days on the red and 10-12 days on the white. The pupal stage lasted 6-8 days on the red and 7-8 days on the white. Three larval instars were identified. Total developmental period from the egg stage to the adult stage ranged from 19-23 days on the red variety and 19-25 days on the white variety. Limited copulation significantly (P<0.05, t-test) increased oviposition and longevity periods of female weevils on both varieties. However, there was no significant difference in the number of eggs laid by females with limited copulation and those with unlimited copulation. Average percentage hatchability of eggs laid by females with limited copulation was 79.5 % and that of females with unlimited copulation was 85.7%. Cores from sweet potato [Ipomoea batatas (L.) Lam] root tubers (red and white varieties) were presented to Cylas puncticollis in choice- and no- choice bioassays. The red variety was significantly (P<0.05) preferred for oviposition in the choice bioassay. The effect of treatments (fertilizer, furadan, a combination of fertilizer and furadan) on sweet potato weevil populations was evaluated on two varieties in two separate fields. In both fields analysis showed that there was no significant difference (P>0.05, AOV) between the treatments on the weevils’ population. Treatment effect on weevils’ infestation (damage) of tubers on the two varieties was assessed during harvesting. The effects of the treatments did not differ significantly (P>0.05) from each other and from the control. However, furadan moderately reduced tuber infestation (damage) during the two planting seasons.