Abstract
Experiments were conducted in the laboratory, net-house and field of Bangladesh Rice Research Institute and Bangladesh Agricultural University to study the effect of nitrogen, phosphorus and potassium on the growth, physiological characters and chemical composition of rice plant and the key biological parameters of brown planthopper (BPH), Nilaparvata lugens (Stål). The effectiveness of different approaches of chemical control of the pest BPH was also assessed. Three levels of nutrient subsidies 0, 100, 200 kg ha-1 for nitrogen 0, 20, 40 kg ha-1 for phosphorous and 0, 60, 120 kg ha-1 for potassium were evaluated for individual and combined effects. Level of nitrogen and phosphorus was higher in BPH than its host rice plant and it showed that nitrogen was more limiting element for BPH than phosphorus. Nymph of BPH had no preference for rice plants grown with the subsidy of any macronutrient but the adult BPH preferred nitrogen-rich rice plants for feeding and oviposition. The numbers of BPH and its egg laying frequency was higher at the bottom of leaf sheath and low at the leaf blade of nitrogen fertilized rice plants. BPH reared on plants with high nitrogen had higher feeding rates and honeydew secretion, probed less and laid more eggs. While such effect was absent for P and K fertilized plants. The survival, body weight, adult longevity, fecundity, egg hatchability and population development of BPH were adversely affected in nitrogen deficient rice plants. The nymphal duration was found to decrease with nitrogen supplementation in plants resulting in shorter generation time of BPH. Phosphorus fertilization slightly increased the fecundity, body weight and population growth of BPH while high potassium subsidy resulted in lower population build up. The BPH adults developed on nitrogen rich rice plants showed higher tolerance to starvation and the nymph showed a slightly higher but insignificant tolerance to insecticide. The tolerance of BPH to starvation and insecticide was unaffected in P and K fertilized plants. Mirid bug a predator of BPH preferred BPH eggs of N100 fertilized plants but it showed a shifting habit from egg predation to plant feeding on N200 fertilized rice plant. Predatory behavior of the mirid bug remained unchanged with P and K fertilization. Extent of plant damage by BPH was higher in nitrogen rich and potassium deficient rice plants but no effect was found for P fertilization. Relative water content in rice plants fertilized with high nitrogenous fertilizer decreased sharply for the BPH injury. The lowest population of the pest and the natural enemies were found in prophylactic treatment. BPH population was maximum in the treatment of insecticide application at 1st top dressing of urea and it was also higher in the plants with insecticide application at 2nd topdressing of urea. Population of natural enemies was decreased in insecticide treated plots. Economic threshold level (ETL) based insecticide application was effective in controlling BPH successfully in the rice field. Results of the biological parameters of BPH as influenced by nutrient subsidies and the effectiveness of different approaches of chemical control are discussed in relation to the integrated management of BPH, N. lugens.