Abstract
Orthaga exvinacea is one of the major pests of mango crop and the caterpillars defoliate the leaves and thereby reduce the crop yield. Use of synthetic insecticide is the quick method for the control this pest but its uncontrolled usage has resulted in serious lethal effects on non-target organisms and environmental pollution. Botanical insecticides are very effective, safe and ecologically acceptable. In the present study, the impact of methanolic leaf extracts of Clerodendrum infortunatum and Chromolaena odorata on carbohydrate concentration in the haemolymph of sixth instar larvae of O. exvinacea was studied under laboratory conditions. The different concentrations (1% to 5%) of each botanical treated mango leaves were fed to the sixth instar. After 48 hours, larvae were sacrificed to collect haemolymph and the quantitative estimation of carbohydrate has been done. The results showed that there was some noticeable decrease in the amount of carbohydrate in the treated larvae when compared to control. The decrease in level of carbohydrate concentration was correlated with the increase in concentration of botanicals. Among the botanicals tested C. odorata possessed more efficacy than that of C. infortunatum and this experiment reveals the potency of both botanicals to be used as natural biopesticides against this pest.
Highlights
The mango leaf-webber, Orthaga exvinacea Hampson is one of the major pests of mango crop
The carbohydrate concentration of haemolymph was reduced from 10.34 mg/ml to 1.18 mg/ml with the increase in the treatment concentration from 1% to 5% and the maximum of 91.93% reduction in carbohydrate content was noticed at 5% and the minimum of 29.27% reduction was observed at 1% treatment (Table I)
The results of quantitative studies on carbohydrate concentration in haemolymph revealed the potency of both leaf extracts for decreasing the carbohydrate content in the larvae
Summary
The mango leaf-webber, Orthaga exvinacea Hampson is one of the major pests of mango crop. In larval stage, they defoliate the leaves and thereby reduce the crop yield but in adult stage they do not cause any damage to the crop. They defoliate the leaves and thereby reduce the crop yield but in adult stage they do not cause any damage to the crop The infestation by this caterpillar directly affects flowering of the plant and thereby reduce the fruit formation. Earlier, it was considered as minor pest of mango but since last few years, due to its severe infestation and extent of damage caused, it has been reported as a major pest of mango in Kerala [2]. The use of conventional insecticides in pest management programs around the world has resulted in environmental pollution, lethal effects on non-target organisms, pest resistance to insecticides and pest resurgence
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