Evaluation of adipokinetic response in the adult desert locust, schistocerca gregaria under the influence of azadirachtin and melia volkensii extract

Abstract

In order to develop realistic options and control strategies which are enviromentally acceptable, sustainable utilization of indigenous botanical resoursesought to be established. Flight performance was reduced in the desert locust, S. gregaria Forskal after injections of 0.01 gland pairs of co,rpora cardiaca as a standard dose and treatment with a definable triterpenoids (limonoid) fraction extracted from A. indica and Melia volkensii, family Meliaceae. The cc extract only produced a hyperlipaemic response which was approximately double the initial resting lipid levels. From the data obtained in this study a rise in the haemolymph lipid level from 11.98 ± 1.63 ~g/~l at zero time to 28.76 ± 2.97~g/~1 60 minutes from commencement of flight was realised and was significant at p < 0.05. In contrast, the blood lipid levels in azad i"'raoht i n-ct.r eat.ed and flown locusts were less than those in the controls, which received cc extract only. Doses ranged between O.l~g to 2~g of azadirachtin per locust. Using 0.1 ~g - 0.25 ~g/locust of ~ volkensii triterpenoid fraction,the difference in total lipid concent~ation between resting levels and 60 minutes after treatment ranged from 1.!.to 8.9 ~g/~l. A higher M. volkensii dose (0.5-2~g/locust) was not effective in inducing hyperlipaemic response at 60 minutes. Unflown locusts wh.i crr were in jected with cc extract and treated with azadirachtin or ,IvI. volkensii extract showed increased hyperlipaemic response with maximal blood lipid xvi level occur ing bet.weeri 60 and 90 mini ut.es . The CUllLrol gruup which received cc extract unly responded maximally within 30 minutes of treatlllent. The poor flight activity observed in treated lucusts confirmed earlier reports un the physiological effects of triterpenoid compounds. A indica extract showe the highest effect on the reduction of flight speed within the initial 30 minutes. The mean flight speed in control locusts which received cc extract only was 2292 revolutions, while locust treated with 0.1M9 of azadirachtin attained a mean flight speed value of 1688 revolutiuns in the first 30 minutes (76rpm and 56rpm respectively), a difference which was significant at P < 0.05. M. volkensii treaced locusts also had significantly reduced speed compared to the controls. The flight pattern of locusts treated with M. volkensii extract showed a continued drop throughout the experimental period. The control group showed a mean speed of 14rpm "between 60-90 minutes. This was a signicantly high value compared to 6rpm in the treated group for N. volkensii doses above 0 .1ug. A high dose of the M. volkensii extract (0. 5-2 ug/ locust) caused hind leg paralysis two days after treatment in adult S. gregaria.