Phenotype and gene expression comparisons between imidacloprid resistant and susceptible strains of cotton aphid by various environmental pressures

The melon and cotton aphid Aphis gossypii Glover (Hemiptera; Aphididae) is one of the most serious pests worldwide. We surveyed insecticide susceptibility in A. gossypii field populations to 12 insecticides to examine resistance ratios. The levels of insecticide resistance were extremely high, especially to neonicotinoids. One point mutation was found in the beta1 subunit loop D region of the nicotinic acetylcholine receptor (nAChR) of the imidacloprid-resistant strain. Feeding behavior analysis using an electrical penetration graph showed that sublethal doses of imidacloprid had significant effects on the duration of phloem ingestion. In addition, higher doses of imidacloprid induced contact toxicity rather than inhibition of feeding behavior. Temperature and insecticide are two important factors that affect survival, reproduction and other physiological processes of insects. To determine interactions of temperature and insecticide treatment on susceptible and imidacloprid-resistant strains of A. gossypii, adults were exposed to three temperatures (17, 22, and 28℃) or combinations of three temperatures and imidacloprid (LC20), and the expression of several genes (heat shock protein 70, cuticle protein, cytochrome P450, and elongation factor) were analyzed. Additionally, the effect of electron beam irradiation on development, reproduction, and several gene expression of imidacloprid-resistant and -susceptible A. gossypii were compared.