Sublethal effects of chronic exposure to chlorpyrifos or imidacloprid insecticides or their binary mixtures on Culex pipiens mosquitoes

• Published in: Physiological entomology Vol. 44; no. 2; pp. 123 - 132
• Main Authors: Al Naggar, Yahya, Giesy, John P., El Kholy, Samar
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Royal Entomological Society 01.06.2019; Wiley Subscription Services, Inc
• Subjects: Adults; Aquatic insects; Binary mixtures; Chlorpyrifos; Chronic exposure; Culex pipiens; Culicidae; Cups; Detoxification; Diptera; Eggs; Exposure; Females; Fitness; Gene expression; Genes; Health risks; Imidacloprid; Insecticide resistance; Insecticides; Instars; Larvae; Mortality causes; Mosquitoes; neonicotinoides; Oviposition; Pesticide resistance; Pesticides; Population control; Reproductive fitness; Sublethal effects; Toxicity tests; Water pollution effects
• ISSN: 0307-6962; 1365-3032
• DOI: 10.1111/phen.12278

Mosquitoes represent one of the most significant threats to human and veterinary health throughout the world. Consequently, improving strategies for the control of mosquitoes is essential. In the present study, juvenile Culex pipiens (Diptera: Culicidae), the common house mosquito, are chronically exposed to sublethal concentrations of chlorpyrifos (20% of LC50) and imidacloprid (5% of LC50), both separately and as a mixture. Developmental time, the emergence rate of adults and the expression of five selected genes involved in detoxification and resistance to pesticides are assessed. To assess the effects on oviposition choice, gravid females are forced to oviposit into cups containing water with added chlorpyrifos, imidacloprid or a mixture of both. The time required for the development of second‐ and third‐instar larvae is observed to differ significantly between treatments. Adults of C. pipiens fail to emerge from larvae hatched in both imidacloprid and the binary mixture. The expression of the four quantified detoxification genes differs significantly in third‐larval instars exposed to chlorpyrifos and/or imidacloprid compared with controls. Gravid females also fail to lay eggs on water to which either of the insecticides or the binary mixture is added, although they do lay eggs in cups containing water only. Chronic exposure to sublethal concentrations of chlorpyrifos or imidacloprid has significant adverse effects on development and thus the reproductive fitness of C. pipiens and, accordingly, could be used in the population control of these mosquitoes. Chronic exposures of juvenile Culex pipiens to sublethal concentrations of chlorpyrifos or imidacloprid had significant adverse effects on development, pupation, adult emergence and on some detoxification genes quantified. Exposure to either insecticide individually or combined led to complete inhibition of oviposition by gravid C. pipiens. Proactive dosing of water bodies with sublethal concentrations of these pesticides could be used in population control of these mosquitoes.