oa African Entomology - The effect of food plants on metabolic reserves, development and fecundity in the African pest grasshopper. Zonocerus variegatus (Linnaeus) (Orthoptera: Pyrgomorphidae)
Groups of Zonocerus variegatus were placed in cages with food plants. Sixth instar nymphs were supplied with a mixed diet of Manihot esculenta, Vernonia amygdalina and Chromolaena odorata, and a single sample of each of these and Acalypha wilkesiana. The highest growth rate, the most haemolymph and fat body, and the greatest food value in these tissues (carbohydrates, proteins and lipids), were generally found in those grasshoppers fed on the mixed diet and those fed on M. esculenta. Grasshoppers fed on A. wilkesiana and V. amygdalina mostly yielded intermediate, and those on C. odorata the lowest values. Instar duration lasted twice as long on C. odarata. Mixtures of Synedrella nodiflora, C. odorata and Paullinia pinnata, and each of these plus M. esculenta and A. witkesiana, were tested singly on the adults. The best somatic growth was manifest by adult females fed on M. esculenta and A. wilkesiana, and the poorest on C. odorata. On S. nodiflora and the mixture, growth was intermediate. The pre-oviposition period was shortest on M. esculenta and longest on S. nodiflora. The ovaries did not develop on C. odorata and P. pinnata. In late vitellogenesis, the largest ovarioles, containing the most reserves, were found in adult females fed on M. esculenta, and the smallest on S. nodiflora. On A. wilkesiana and the mixture, these were intermediate. Most eggs were produced on M. esculenta, but egg-pod length was constant irrespective of food plant. It was concluded that a mixed diet, even of relatively poor plants, is generally more beneficial than single food plants.
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