Sublethal effects of thiacloprid and eforia on life table and detoxification enzymes activity of Schizaphis graminum and predator Hippodamia variegata

Aeinechi, Pezhman (2019) Sublethal effects of thiacloprid and eforia on life table and detoxification enzymes activity of Schizaphis graminum and predator Hippodamia variegata. Masters thesis, University of Mohaghegh Ardabili.

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Abstract

Research Aim:The greenbug, Schizaphis graminum (Rondani) is one of the important wheat pests that can restrict the production of this crop by feeding and transmistting pathogenic viruses. The predatory ccoccinellid, Hippodamia variegata (Goeze) is one of the most important predators of the aphids and has a high potential in control of the aphids in different agroecosystems such as field, horticultural and greenhouse crops. Insects may use biochemical resistance to caunter the chemical compounds, in which the pesticide can be neutralized by one or more different types of enzymes before reaching the site of action. In the present study, the effects of sublethal concentrations of two insecticides, thiacloprid and eforia, on adults of S. granarium and third instar larvae of H. variegata were investigated. Research method:The bioassays were performed by immersing the wheat leaves in insecticidal solution for 10 seconds and placing adults aphids on them. In the case of H. variegata, topical application was used on dorsal segement of third instar larvae.Sublethal effects (LC10 and LC30) of these insecticides were also evaluated on the life table and some biochemical parameters of S. granarium and H. variegata at 27±2°C, 70±10% relative humidity and 16 h light and 8 h darkness photoperiod. Side effects of the pesticides were also estimated using the method provided by the International Organization for Biological Control (IOBC). Conclusion:The LC50 values of thiacloprid and eforia were 212.7 and 203.9 ppm for S. graminum and 730.3 and 713..3 ppm for H. variegata,respectively. The results showed that fecundity in both tested insects and adult life span of S. graminum exposed to pesticide treatments were significantly decreased compared to control.Among the treatments, the LC30 of eforia showed the highest toxicity compared with other treatments. The intrinsic rate of increase (r), net reproductive rate (R0), gross reproductive rate (GRR) and finite rate of increase (λ) decreased in both insecticides treatments compared to control. The lowest r value of tested insects was in LC10 and LC30 treatments of eforia. According to the IOBC classification, both treatments of thiacloprid and LC10 of eforia were harmless on H. variegata. Moreover, the LC30 of eforia was slightely harmful on H. variegata. The treatment by tested insecticides had not significant effect on alpha-esterase activity of both insects. Also, the treatments showed no significant effect on the beta-esterase activity of H. variegata, but beta-esterase activity of S. graminum increased in LC30 treatment of eforia and thiacloprid. Acetylcholinesterase and glutathione s-transferase activity of H. variegatashowed no significant difference from control. Glutathione s-transferase activity of the aphid increased 24 h after treatments by LC30 of both insecticides. According to the results of this study, eforia and thiacloprid had negative effects on demographic and biochemical parameters of S. graminum. Thus, LC10 of eforia and LC30 of thiacloprid can be recommended incontrol of S. graminum. Also, these treatments were harmless for H. variegatabased on IOBC classification and hadn’t any effect on its enzyme activities.

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