Comparing the efficacy of some chemical and non-chemical insecticides for control of cotton bollworm, Helicoverpa armigera (Hübner) under cotton field conditions

Background and Objectives
Cotton bollworm (Helicoverpa armigera) is a major economic pest worldwide and damaging many crops. Microbial insecticides, botanical insecticides, and insect growth regulators (IGRs) are among the compounds used as biorational insecticides in integrated pest management programs. Due to the high dependence of this pest control on insecticides application, investigating effective and safe insecticides is an important research topic.
Materials and Methods
To evaluate the effectiveness of different insecticides to control this pest, an experiment was conducted in a randomized complete block design with nine treatments in a cotton field in Golestan province. Treatments included indoxacarb, teflubenzuron+alpha cypermethrin, thiodicarb, cypermethrin, chlorfluazuron, lufenuron+emamctin benzoate, matrin and Bacillus thuringiensis. The control plot was treated with water. The plots were treated 7-10 days after the peak flight of the moths. Sampling was performed one day before and 1, 2, 4, 7, 14, 21 and 30 days after treatment. At each sampling time, 10 plants were randomly selected for each replicate, and the number of live larvae was counted.
Results
One day after treatment, the highest efficacy was recorded for thiodicarb (63.4%) and then for teflubenzuron+alpha cypermethrin, lufenuron+emamctin benzoate and indoxacarb with 58.1, 46.7 and 44.3%, respectively. After four days, when the mean larval population in all 10plants in the control treatment was still at the pre-treatment level, the effectiveness of these insecticides was 77.6, 81.2, 89.9, 79.8, 51.6, 83.3, 47.9, and 46.4%, respectively. Two weeks after the treatments, no larvae were observed in the plots sprayed with thiodicarb, cypermethrin, and lufenuron+emamctin benzoate, and their effectiveness in reducing the pest population was 100%. At the endpoint of the experiments, the efficacy of Bt, Matrin, chlorfluazuron, and Indoxacarb were 48.5, 55.5, 58.2, and 89.8%, respectively. The other four treatments (cypermethrin, lufenuron+emamctin, teflubenzuron+alpha cypermethrin, and thiodicarb) were completely (100%) affected the larvae population.
Discussion
According to the standard classification of insecticides toxicity provided by the World Health Organization (WHO), the insecticides alpha cypermethrin, emamctin benzoate, indoxacarb, thiodicarb and cypermethrin are all classified as the group with moderate toxicity, lufenuron with low toxicity and teflubenzuron and chlorfluazuron were classified in the group without toxicity. The results demonstrated that two relatively safe insecticides, teflubenzuron+alpha-cypermethrin, and lufenuron+emamctin benzoate, are suitable alternatives to common insecticides, indoxacarb, and thiodicarb. Matrin, plant-derived insecticide, Bt, microbial insecticide, and chlorfluazuron, IGR insecticide, were relatively effective. Due to the adverse effects of using common chemical insecticides, two insecticides, teflubenzuron+alpha-cypermethrin, and lufenuron+emamctin benzoate, are recommended as alternatives concerning the relative safety and simultaneous use of chlorfluazuron with matrin/Bt as entirely safe options.