Management of the African grasshopper, zonocerus variegatus (l.) (orthoptera: pyrgomorphidae) in ghana: the role of chromolaena odorata

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2005-11-03
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The pestilence of the variegated grasshopper. Zonocerus variegatus, was investigated whether it was attributed to the introduction and spread of the weed. Chromolaena odorata in Ghana. and the consumption of pyrrolizidine alkaloids (PAs) from the flowers of the plant by the insect. The study was aimed at developing an effective control measure against the pest. Questionnaire and ecological surveys were conducted to determine the distribution patterns and densities of’ the insect and plant in different ecological zones in the country. traversing natural vegetations. Studies were conducted on the biology of Z. variegatus with respect to diet with and without source of PAs. The attraction of Z. variegatus to the PAs in the dry roots of C. odorata. Heliotropiurn indicum and Crotalaria refusa were compared while Carbofuran® 3G. Perfekthion® 40 EC and Karate® 2.5 EC were screened for their efficacy as killing agents for the grasshopper. The survey results established a correlation between the distribution of C. odorata and the pestilence of’ Z. variegatus. While Z. variegatus is distributed nationwide. C. odorata has spread as far north as Lat. 8º 30’ N from the Coast, an increase of 15’ within a decade. In areas with no C. odorata, Z. variegatus was univoltine and not a serious pest. However, below Lat. 8º 30’ N where C. odorata occurs, Z. variegatus exists in two distinct wet and dry season populations with the dry season population being a major pest on food crops and forestry products. This observation was traced to the pharmacophagous utilization of PAs horn the flowers of C. odorata during the dry season by the insect. The diet studies showed that Z. variegatus utilises PAs which are secondary plant metabolites. Diet with a PA-source as a component positively enhanced growth. egg production and life-span of the grasshopper. All stages of the insect were attracted to the PA-sources and 300 g weight of the dry chopped roots of C. odorata showed promise for use as the PA-lure component for the development of PA-based attracticide to manage Z. variegatus. Incorporating 1.0% Carbofuran® 3G (w/v) into the dry chopped roots of C. odorata yields a potent cost effective PA-based attracticide for the management of Z. variegatus in open fields and on cabbage. Thus, farmers at the community level can adopt this management option as a contribution to the management of’ Z variegatus. Notwithstanding the present achievement on the use of PA sources as attractants for the integrated management of’ Z variegatus, it. is conceded that further investigations on the biology and the development of PA-based attracticide baits with both chemical and biological insecticides for the management of Z. variegatus are required.
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A thesis submitted to the College of Sciences in partial fulfilment of the requirements for the award for the degree of Doctor of Philosophy, 2005
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