Insecticide resistance and population genetics of Aedes albopictus introduced populations in mainland Portugal

The Asian tiger mosquito Aedes albopictus is a major threat to public health
due to its ability for dengue, chikungunya and Zika virus transmission. This
mosquito species has rapidly spread from Asia and is now considered one of
the most invasive species worldwide. In Europe, the invasion started in
Albania in 1979, having spread to 26 countries, including the Iberian
Peninsula. During 2017, new detections of Ae. albopictus populations were
recorded in Portuguese locations such as Penafiel (North) and Vilamoura
(South). Therefore, this study aims to assess the genetic diversity and
structure of Ae. albopictus using microsatellite markers and to assess
insecticide susceptibility and presence of kdr mutations in both mosquito
populations. Aedes albopictus larvae were sampled mainly from storm drains
and reared in the insectary to produce an F1 generation to be used in
susceptibility bioassays. Adult mosquitoes were sampled by landing
collections and kept for genetic analyses. Six insecticides were tested using
WHO assays and discriminant doses: Permethrin (0.25%), Deltamethrin
(0.03%), Cyfluthrin (0.15%), Fenitrothion (1%), Bendiocarb (1%) and DDT (4%).
Results showed susceptibility to pyrethroid insecticides (mortality >99%) but
suspicion of reduced susceptibility to non-pyrethroid insecticides. Genomic
DNA was extracted using the NZY tissue gDNA isolation kit (NZYtech, Portugal). Genotyping of commonly present kdr mutations in this species
revealed the absence of these mutations in Portuguese populations.
Microsatellite markers were genotyped using previously published protocols
and sent to Yale DNA Analysis Facility at Yale University for fragment analysis.
Although our data indicates that in Algarve the mosquito might have arrived
very recently, the diversity and genetic composition of the mosquito
population in Penafiel indicates that in that location we have a well-established population. The fact that the mosquitoes were collected in a tire
company might be related with possible multiple introductions in that site.
Tires are imported from many suppliers including European and Oriental
countries throughout the year and passive transportation of eggs should be
an issue. The detection of Ae. albopictus populations in Portugal poses an
important health risk for the human population. Therefore, controlling the
spread of Ae. albopictus is mandatory to prevent and reduce the incidence of
these diseases.