Effects of Selection to Diflubenzuron and Bacillus thuringiensis Var. Israelensis on the Overwintering Successes of Aedes albopictus (Diptera: Culicidae)

SIMPLE SUMMARY: Aedes albopictus is an invasive mosquito species that is well established in many parts of Europe and poses high risks of autochthonous transmission of chikungunya and dengue viruses. The high dependency on commonly used larvicides such as Diflubenzuron (DFB) and Bacillus thuringiensis var. israelensis (Bti) to control its populations raise concerns for resistance development. Although studies addressing the potential for development of resistance in Ae. albopictus against these two important larvicides are essential for planning control programmes, no such data are available. Here, by imposing an increasing selective pressure to DFB and Bti over nine successive generations on a recently laboratory established Ae. albopictus population we determined the subsequent resistance levels and corresponding overwintering success of the selected populations relative to control (colonies that received no selection). Our findings revealed a moderate and a minor increase on the resistance levels following selection with DFB and Bti, respectively. No significant differences were observed regarding the overwintering successes between the two selected populations and the control, which suggests that the selected individuals retain an equal ability to persist in the wild on an annual base. ABSTRACT: Aedes albopictus is an invasive mosquito species responsible for local transmission of chikungunya and dengue viruses in Europe. In the absence of available treatments, insecticides-based control remains one of the most important viable strategies to prevent emerging problems. Diflubenzuron (DFB) and Bacillus thuringiensis var. israelensis (Bti) are among the most commonly used larvicides for Ae. albopictus control with consequent concerns for the potential development of resistance. Studies on the resistance emergence in Ae. albopictus and its persistence in the wild to both DFB and Bti are essential for the efficient and sustainable planning of the control programmes. In this context, larvae from a recently laboratory established population were subjected to increasing selective pressure for nine successive generations using both DFB and Bti. The resistance levels and the overwintering success of the selected populations relative to control (colonies that received no selection) were determined. Results revealed an 8.5- and 1.6-fold increase on the resistance levels following selection with DFB and Bti, respectively. The selection process to both larvicides had no apparent impacts on the overwintering capability relative to control, suggesting the successful persistence of the selected individuals in the wild on an annual base.