Comparison of the effectiveness of some bio- and conventional insecticides for the control of rice stem borer, Chilo suppressalis Walker (Lep.: Crambidae) in Gorgan

Rice stem borer, Chilo suppressalis Walker (Lep.: Crambidae), is one of the most important and destructive rice pests in the world, including Iran, especially in the northern provinces. Every year, a significant amount of chemical insecticides are introduced into the environment to control this pest, which has caused many concerns in human health (rice farmers and consumers) and other organisms (aquatic, birds, livestock, etc.). Therefore, replacing high-risk chemical insecticides with environmentally friendly and safe compounds can reduce the side effects of pesticides and reduce the occurrence of resistance in this pest to the insecticides used and, as a result, control it more effectively. This study was conducted to compare the effectiveness of several common biological and chemical insecticides to control the rice stem borer, C. suppressalis.For this purpose, a study was designed as a randomized complete block design with six treatments and four replications and was carried out in a field located in Hashemabad village, Gorgan city, Iran. The experimental treatments included chlorpyrifos (Dursban®, EC 40.8%, 2 L/hectare), fipronil (Regent®, SC 50%, 1 L/hectare), fenitrothion (Sumithion®, EC 50%, 1.5 L/hectare), B.T. (1 L/hectare), Matrin (Rui Agro®, SL 0.6%, 1 L/hectare), and a control group (water foliar spraying). Additionally, the larval population was sampled one day before foliar spraying and 3, 7, and 14 days after foliar spraying. The Henderson-Tilton formula was used to calculate the mortality rate (insecticide efficiency). Analysis of variance was performed using the GLM model with SAS software.Means were compared using Duncan's multi-range test at the 5% probability level.The analysis of variance indicated significant differences among the treatments in terms of stem infection percentage and death of the central bud at 7 and 14 days after treatment application. Additionally, the analysis of variance results for stem contamination after 14 days of insecticide application revealed that all insecticides could reduce stem contamination compared to the control treatment, with some insecticides falling within the same statistical group. Regarding the effectiveness of the treatments in controlling the rice stem borer, the analysis of variance results showed that chlorpyrifos, Matrine, and fipronil were the most effective insecticides, followed by fenitrothion and BT, at 3 days after treatment application. At 7 days after treatment application, chlorpyrifos exhibited the highest efficiency, averaging 81.24%, which was not significantly different from fipronil and Matrine. Fenitrothion and BT insecticides demonstrated the lowest efficiency. The same trend persisted 14 days after treatment application, with chlorpyrifos achieving the highest efficiency at an average of 85.85%. There were no significant differences between chlorpyrifos, fipronil, and Matrine, which had efficiencies of 79.65% and 78.97%, respectively. BT insecticide recorded the lowest efficiency level at 54.18%, which was significantly different from the other insecticides.Based on the present study's findings, it is evident that insecticides such as Chlorpyrifos and Fipronil, which have been extensively used in Iran for the chemical control of the rice stem borer, have raised concerns regarding the development of resistance in this pest. Therefore, it is advisable to consider alternatives such as Matrine, which is safer and less hazardous. Matrine, with its distinct mode of action, can serve as a highly suitable option for controlling the rice stem borer while reducing the likelihood of resistance development against insecticides.