Phenotypic insecticide resistance status of the Culex pipiens complex: a European perspective

Abstract

Background: The common house mosquito Culex pipiens is known to be a major vector for West Nile virus. In order to decrease risks of West Nile virus outbreaks in Europe, insecticides and the bio-larvicide Bacillus thuringiensis israelensis (Bti) are commonly used for vector control. Alarmingly, insecticide resistance has been reported in Cx. pipiens populations from Southern Europe and several countries neighbouring Europe. For Central and Northern Europe, however, the phenotypic insecticide resistance status of Cx. pipiens has not yet been investigated.

Methods: A literature review was performed to assess the geographical distribution of insecticide resistance in Cx. pipiens. To fill the gap of knowledge for Central and Northern Europe, WHO susceptibility tests with permethrin, deltamethrin, malathion, bendiocarb and DDT and a larval toxicity test with Bti were performed with a Cx. pipiens population from Belgium, a country in Central Europe.

Results: This research provides the first evidence of widespread phenotypic insecticide resistance in Cx. pipiens. In general, Cx. pipiens developed resistance against multiple insecticides in several countries. Another Cx. pipiens population from Belgium was tested and showed insecticide resistance against deltamethrin, permethrin, DDT and possibly against bendiocarb. The bio-larvicide Bti caused lower mortality than reported for other Cx. pipiens populations in the literature.

Conclusions: These results indicate the urgent need for insecticide resistance monitoring against commonly used adulticides and larvicides in Europe, for the translation of knowledge gained regarding the limited efficiency and availability of insecticide into EU legislation and the need for innovative non-chemical vector control tools in order to counter the widespread insecticide resistance in Culex populations.

Keywords: Bacillus thuringiensis israelensis; Belgium; Bioassays; Culex pipiens molestus; DDT; Deltamethrin; Permethrin; Phenotypic resistance; Vector control; WHO susceptibility test.

Fig. 1

Insecticide resistance status in Cx. pipiens. Resistance towards a permethrin, b deltamethrin, c malathion, d bendiocarb, e DDT, f Bti. f WHO larvicidal susceptibility test with Bti on the Belgian population. Insecticides approved by the EU are a, b, d, f; insecticides for which the Belgian population is susceptible/possibly resistant are c, d; insecticides for which the Belgian population is resistant are a, b, e, f. Black indicates Belgian population, dark grey EU, light grey neighbouring countries to EU, white outside EU

Fig. 2

Countries coloured by insecticides resistance status of Culex pipiens for the five tested insecticides. Light red indicates possible resistance towards tested insecticides, dark red indicates high resistance towards tested insecticides