Development of Resistance to Chlorpyrifos in Culex pipiens (Diptera: Culicidae) Population under Temephos Selection Pressures

Development of resistance to chlorpyrifos in Culex pipiens population from Tunisia under temephos selection pressures was investigated. The objective of this study was to follow the evolution of resistance responses in Culex pipiens larvae under laboratory conditions. The selection to temephos caused a significant increase of resistance to chlorpyrifos levels. Indeed, the LD50 resistance rate increased from 75.90 in the natural population to approximately 6620.66 in the 4th generation of selection. This resistance dropped sharply in the 5th generation (1686.35) to increase again in the last generation of selection reaching 3929.36. The reason for this unstable variation is unknown and effects related to uncontrolled environmental parameters and/or inter-strain genetic variability is probably involved. Our results showed the involvement of insensitive acetylcholinesterase (AChE), which is a common target for temephos and chlorpyrifos insecticides, in the recorded resistance. The potential to develop resistance to the chlorpyrifos is very clear in this species.