Effects of Melia volkensii crude extracts on feeding , food untilisation, growth and fecundity of the desert locust
Kariuki, Ndathi Obadiah
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Crude extracts from M. volkensii (Gurke) plant parts exhibited differential effects on feeding, food utilisation and fecundity in Schistocerca gregaria (Forskal). The rate of feeding was different in different nymphal developmental stages of the locust. Fledglings showed higher feeding rates at higher extract doses than the young and old nymphs. However, the rate of feeding varied at lower doses. The antifeeding effects followed a dose dependent fashion thus being low at lower extract doses and high at higher concentrations. The antifeeding effects also differed between extracts from different parts of M. volkensii. Fruit and leaf extracts exhibited higher antifeeding levels than stem bark and root extracts and distilled water. The effects of the extracts also depicted a dose-dependent fashion where 6.0% of M.volkensii extracts showed higher antifeedancy while 1.5% had the lowest (p<0.001). M. Volkensii extracts delayed moulting in the locust nymphs resulting to longer period taken to reach adult stage. However, different extract types did not show significant differences in arresting ecdysis, but differed significantly from the control sets (p<0.01). Weight increase in the locust nymphs was affected by the crude extract of M. volkensii, though; the values obtained in this study didn't differ significantly from the control sets (p>0.05). The mode of application of M. volkensii extracts to the locust showed differential effects on growth and development of the nymphs. Topically treated nymphs grew and developed of the nymphs. Topically treated nymphs grew and developed at a slow rate and showed growth abnormality especially when the extracts were from the fruits and leaves. The effects here exhibited more potency than when extracts were applied to the food material or when treated to the soils in which the sorghum feedings were grown (p<0.001). Mean growth ratios of the selected structures of the locust differed significantly between the extracts. Fruit and leaf extracts exhibited higher negative effects resulting to lower growth rates than those of the stem, root and distilled water (p<0.001). Higher mortality was recorded in nymphs treated with fruit and leaf extracts. Death rate of the nymphs also differed between different instars, where older nymphs and adults (fledglings) recorded higher rates than young nymphs (p<0.05). This reflected cumulative effects of the extracts in the course of growth and development of nymphs. There was also an evident compensation by the locust nymphs, for the reduced food ingestion observed after extract treatment. This was especially by the fledglings, which exhibited higher levels of food utilisation in terms of conversion of digested and ingested food into body substance (E.C.D and E.C.I), (p<0.001). However growth rate was not significantly increase in growth rate than in the control sets (p<0.001). There was a significant reduction in fecundity of the locust when topically treated with M.Volkensii extracts. The extracts significantly reduced the mean number of pods produced by the locust (p<0.01) and the mean number of nymphs emerging per pod (p<0.01) and the mean numbers of nymphs emerging per pod (p<0.05). Fruit and leaf extracts showed higher potency to this effect than those from the bark, root and distilled water. Differential effects of the extracts on successive population mortality on locust sexes was evident, leading to significantly higher levels of 100% (p<0.05). Males were more vulnerable to extracts than females. Roots and stem bark extracts however, had minimal effects on the locust performance.