Supplementary material to JEMCA 20230005: Efficacy of biological larvicide VectoMax® FG against Aedes albopictus and Culex pipiens under field conditions in urban catch basins
The invasive Asian tiger mosquito Aedes albopictus appeared in southern Switzerland in 2003 and is currently well established in most of its urban regions. In public areas, the control measures against the mosquito focus on its aquatic phase with removal of breeding sites and applications of larvicides at sites that cannot be eliminated. Larvicidal products are applied mainly to catch basins, one of the major sites of oviposition for both Ae. albopictus and Culex pipiens in urban areas. We evaluated the efficacy of a larvicidal formulation (i.e. VectoMax® FG), combing the action of spore-forming bacteria Bacillus thuringiensis var. israelensis and Lysinibacillus sphaericus, against Ae. albopictus, Cx. pipiens and non-target organisms present in urban catch basins. We used floating adult emergence traps to compare the number of adults emerging from 38 catch basins treated once during the study period with ten untreated (control) catch basins. The catch basins were monitored for 21 weeks and the efficacy was evaluated fitting a Generalised Additive Mixed Model (GAMM). The efficacy of the treatment varied among species. It was high against Cx. pipiens (100% reduction in emerging adults at maximal efficacy) and lower against Ae. albopictus (60% reduction). This suggests that it is important to examine target species separately when evaluating the efficacy of larvicidal products. The product showed a long residual larvicidal activity with the number of emerging adults still being reduced by 75% for Cx. pipiens and 60% for Ae. albopictus at ten weeks after the treatment. We also observed that the maximal efficacy of the product was reached about two weeks after the treatment. The effect on non-target organisms, specifically, chironomids, was also strong (80% reduction). However, their numbers raised again rather quickly (i.e. after two weeks), and the effect vanished around week 11.