Factors Affecting Insecticide-Induced Resurgence of the Brown Planthopper, \u3ci\u3eNilaparvata lugens\u3c/i\u3e on Rice

Resurgence of the brown planthopper, Nilaparvata lugens (Stål) on rice was induced by applications of decamethrin, methyl parathion, and diazinon. Differential mortality of predators and hoppers did not appear to be the primary factor for resurgence. Hoppers appeared to be attracted to methyl parathion and decamethrin treated plants because of plant growth. Improved plant growth, however, did not compensate for the increased feeding of the insecticide-treated hopper population, and plants treated with resurgence-causing insecticides succumbed to feeding injury earlier than untreated plants. Population increases were due in part to stimulation of reproduction of the hopper, either by contact action of the insecticides or through increased plant growth. Reduction in the length of the nymphal stage and increased adult longevity resulting in a shortened life cycle and longer oviposition period, respectively, were additional factors contributing to resurgence

Laboratory Investigations on the effect of Insecticides and Host Immunisation for Control of Tick Infestation

The thesis is in two parts. In the first, three species of economically important African ixodid ticks, Rhiplcephalus appendiculatus, Amblyomma hebraeum and Amblyomma variegatum were investigated for the first time for their susceptibility to three newly developed photostable synthetic pyrethroids with long residual activity, permethrin, cypermethrin and decamethrin. Results of tests on unfed larvae, unfed nymphs and unfed adult ticks using different methods of testing such as the immersion technique, dipping, impregnated packet technique, "tea bag ” technique and topical application are presented, and the relative susceptibility of the different species and of different developmental stages to the three pyrethroids is compared. A limited number of experiments were also done on the effect of the compounds on engorged nymphal ticks. The potential of the synthetic pyrethroids in the control of multi-host tick ecto­parasites of animals in Africa is discussed. The second part of the thesis is concerned with investigations on acquired immunity or resistance in host animals to tick infestation and its role in tick infestation of animals. This was investigated by using small animal models, rabbits and guinea pigs, and four speciesof ixodid ticks, R. appendiculatus, A. hebraeum and A. variegatum and an European species, Dermacentor marginatus. The development of immunity in the animals following a primary infestation with one species of tick, to a second infestation with the same species, and of cross-immunity to a second species, were investigated. Sera from immune animals were tested by serological methods for antibodies to tick salivary gland antigens. In a limited series of experiments, infection of animals with blood pathogens and the injection of tick cell extracts and larval tick homogenates into animals were investigated for their effect on development of immunity to tick infestation. The role of chemical acaricides and of acquired host immunity as an alternative or additional method to chemical control in the overall strategy of tick management on animals is discussed in the light of results obtained from the investigations

Resurgence of \u3ci\u3eNilaparvata lugens\u3c/i\u3e (Stål) Populations as Influenced by Method and Timing of Insecticide Applications in Lowland Rice

Resurgence of Nilaparvata lugens (Stål) after insecticide application is a common phenomenon in rice in South and Southeast Asia. Among other insecticides inducing resurgence, carbofuran, decamethrin, and methyl parathion were selected for this study. Of the various methods of carbofuran application tested, foliar sprays were most active in inducing resurgence. Extent of resurgence was highly influenced by time of insecticide application. Sprays of methyl parathion and decamethrin applied 50 and 65 days after transplanting (DT) induced resurgence in the third generation of N. lugens at ca. 90 DT, whereas earlier applications had little effect. The cause(s) for resurgence was not definitely established, but stimulation of N. lugens reproduction appeared to be of more significance than destruction of natural enemies

Relative Efficacy of Different Insecticides Againsts Chilli Pod Borer, Spodoptera Litura Fabr. (Lepidoptera - Noctuidae) in Manipur

ABSTRACT: The bio-efficacy of seven insecticides namely Endosulfan (0.07%), Monocrotophos (0.05%), Malathion (0.05%), Dimethoate (0.04%), Phosalone (0.04%), Cypermethrine (0.01%) and Neem oil (3.5%) were applied on Chili. Capsicum annum was grown in the field for the control of Chilli pod borer, Spodoptera litura Fabr. The insecticide like Phosalone (0.04%) and Endosulfan (0.07%) were most effective and the neem oil were found to be the least effective in reducing borer population.Â