Toxicity of five insecticides against the Ostrinia furnacalis (Guen.), Spodoptera litura (F.) and Heliothis armigera (Hubn.) and their effects on Apis mellifera L. in hybrid and open-pollinated varieties of sunflower (Helianthus annuus L.)

Comparison of efficacy of five insecticides against Ostrinia furnacalis (Guen.), Spodoptera litura (F.) and Heliothis armigera (Hubn.) were studied in the laboratory and experimental fields. In the laboratory, using the topical application method, LC50 values were determined. The results were represented various in different insect species and different instars. Cypermethrin, deltamethrin and endosulfan were the most toxic to the first and second instar larvae. Monocrotophos was the least toxic to the first and second instar larvae. The second instars were more resistant to insecticides than the first instar for all insecticides. The experimental field studies were conducted at the Lopburi Agricultural College, Amphur Pattananikom, Lop Buri Province during the wet and dry seasons. The experiments were arranged in split-plot in randomized complete block design (RCB) with four replications. Main plots were open-pollinated variety (Synthetic 3) and hybrid variety (Hysun 33) of sunflower, and sub plots were five insecticides and a control. There were no significant difference among treatments. Endosulfan was slight better in controlling the larvae than the others. All insecticides tended to show better for controlling the larvae and gave better seed yields than the controlled treatment. However, deltamethrin endosulfan and fenvalerate tended to be the best. Hybrid variety gave higher seed yields than open-pollinated variety in pollinator and insecticide application condition. The study on the residue toxic of insecticides in the field test was determined by number of dead honey bee after put into the net bag which covering the sunflower after application. The experiment was designed in split-plot in randomized complet block design (RCB) with five replications. One, three and seven days after application were arranged to main plots, and five insecticides and a control were designed to sub plots. Cypermethrin and monocrotophos were the most toxic and fenvalerate was the least toxic to the honey bees. One and three days after application were not significant difference toxic to the honey bees. Residue toxic at seven days after application was less than the others. Endosulfan was the best detoxic in the field test.