Kamal Kumar Gupta

Impact of the Stem Extract of Thevetia neriifolia on the Feeding Potential and Histological Architecture of the Midgut Epithelial Tissue of Early Fourth Instars of Helicoverpa armigera Hübner

Helicoverpa armigera HÜbner is one of the most important agricultural crop pests in the world causing heavy crop yield losses. The continued and indiscriminate use of synthetic insecticides in agriculture for their control has received wide public apprehension because of multifarious problems, including insecticide resistance, resurgence of pest species, environmental pollution, and toxic hazards to humans and nontarget organisms. These problems have necessitated the need to explore and develop alternative strategies using eco-friendly and biodegradable plant products. In view of this, the efficacy of Thevetia neriifolia methanol stem extract was evaluated against the early fourth instars of H. armigera as an antifeedant and stomach poison agent. Feeding of larvae with the diet containing 0.005%–5.0% extract resulted in 2.06%–37.35% antifeedant index; the diet with 5.0% extract caused 54.3% reduced consumption. The negative impact of extract on larval feeding resulted in 37.5%–77.7% starvation, causing adverse effects on the larval weight. Choice between control and experimental diet resulted in feeding preference of larvae for the control diet, leading to 7.3%–42.9% reduced consumption of extract-containing diet. The only exception was the diet with 0.005% extract, which could not cause any deterrence. The midgut histological architecture of H. armigera larvae fed with 0.005%–0.05% extract-containing diet with negligible antifeedant potential showed significant damage, shrinkage, and distortion and vacuolization of gut tissues and peritrophic membrane, causing the disintegration of epithelial, goblet, and regenerative cells; the damage increased with the increase in concentration. These changes in the gut caused negative impact on the digestion and absorption of food and thus nutritional deficiency in the larvae, which could probably affect their growth and development. This study reveal the appreciable stomach poison potential of T. neriifolia stem methanol extract against H. armigera larvae, which can be explored as an eco-friendly pest control strategy.

Sublethal Effects of Ethanol Extract of Ocimum sanctum on Laboratory Bred Population of Dengue Mosquito Aedes aegypti L. (Diptera: Culicidae)

Objectives: Aedes aegypti is a vector of several diseases which cause serious discomfort and fatality to human being. Current investigations were carried out to assess sublethal effects of ethanol extract of the leaves of Ocimum sanctum against A. aegypti in order to find ecofriendly alternatives for integrated vector management‟. Methods: Lethal and sublethal effects of ethanol extract of O. sanctum against fourth instar larvae were assessed by using WHO protocol. The studies were extended to evaluate the effects of the extract on growth and development of the treated larvae. The chemical components present in the extracts were analyzed by Gas chromatography and mass spectroscopy (GC-MS). Results: Exposure of fourth instar larvae of A. aegypti revealed moderate toxicity. However, the treated larvae exhibited mortality during subsequent days of exposure. The treatment with the extract also has adverse impact on growth and development of the larvae. Consequently there was increase in the larval duration in the treated larvae. Larva-pupa intermediate and pupa-adult intermediate were the developmental anomalies observed in the treated fourth instar larvae. This suggested presence of juvenile hormone mimic or juvenile analogue activity in the ethanol extract of O. sanctum leaves. Presence of farnasene, a derivates of the intermediates in the juvenile hormone biosynthesis was reported in the GCMS analysis of the extract. Conclusion: Our studied indicated moderate lethal and efficient sublethal effects of ethanol extract of O. sanctum against A.aegypti. The bioactive compounds present in the extract, individually or synergistically may be used in formulating a strategy for the mosquito management

Growth regulatory and growth inhibitory effects of Thevetia neriifolia stem extracts on Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract Helicoverpa armigera, a serious global destructive pest of agricultural crops, is on continuous rise despite several control measures undertaken. The detrimental effects of these measures have created a dire need to explore alternate eco-safe strategies. The present study investigates the growth-regulatory and growth-arrest potential of hexane and methanol extracts of Thevetia neriifolia stems against H. armigera. Investigations revealed that larval feeding and rearing on the extract-containing diet did not result in appreciable larval mortality but delayed the larval growth and development. Both the extracts demonstrated dose-dependent effects exhibiting negative correlation between the weights gained by developmental stages and the extract concentrations. Feeding with extracts also resulted in formation of few larval–pupal and pupal–adult intermediates and significantly reduced percent adult emergence of H. armigera. Current study, however, revealed higher growth inhibitory potential of methanol extracts as compared with hexane extracts. The study attempts to provide an eco-friendly approach for H. armigera management.