COMPARATIVE EFFICACY OF SOME INSECTICIDES AGAINST MAIZE APHID (Rhopalosiphum maidis) AND ITS INFLUENCE ON NATURAL ENEMIES IN MAIZE ECOSYSTEM

Abstract

The maize aphid, Rhopalosiphum maidis is one of the most serious pests of maize crop in Bangladesh. Nowadays, it becomes a major barrier for production of maize due to create hamper of pollination. In the present research investigation, the field efficacy of some insecticides was evaluated against maize aphid infestation and their toxic effects were also studied on some natural enemies in the maize ecosystem. To achieve the research goal, a field experiment was conducted on maize at the Entomology Field Laboratory, Department of Entomology, Bangladesh Agricultural University (BAU), Mymensigh during Rabi season of 2017-18. The experiment was set up in Randomized Complete Block Design (RCBD) with five treatments (Imidagold 20SL@ 0.1, 0.3 & 0.5ml/L; Ambush 1.8EC@ 1.5, 2.5 & 3.0ml/L; Hadhak 45WP@ 0.2, 0.4 & 0.6g/L; Suspend 5SG@ 0.5, 1.0 & 1.5 g/L and Heron 5EC @ 0.5, 1.0 & 1.5ml/L) and three replications for each treatment. Maize viz. BARI Hybrid Butta-09 was used as experimental crop. Data were collected on percent reduction of plant infestation & population of natural enemies, yield attributes and benefit cost ratio (BCR). Result clearly indicated that these mentioned parameters were highly significant with the application of insecticides. However, Imidagold 20SL@ 0.5ml/L resulted in the greatest (77.27%) percent reduction of maize plant infestation, the highest (623.51) number of grain per cob, the maximum (39.74g) 100 grain weight, the highest (10.02 t/ha) grain yield, the highest (63.27%) percent grain yield over control and maximum (1.56) benefit cost ratio compared to others tested insecticides which was statistically similar with the dose of 0.3ml/L of Imidagold 20SL. And then, this result was followed by Ambush 1.8EC, Hadhak 45WP, Suspend 5SG and Heron 5EC, respectively. Besides, the highest (93.67%) percent cumulative mean of maize plant infestation, the lowest (330.45) number of grain per cob, minimum (13.43g) 100 grain weight, the lowest grain yield (3.68 t/ha) and the lowest benefit cost ratio (0.95) were obtained from untreated control. With a view to know the toxic effect of different insecticides, the percent reduction of population of natural enemies was counted at 2 days, 5 days and 7 days after spraying. In all field trials, the harmful effects of the five insecticides were in the following rank order (least harmful to most harmful): Imidagold 20SL