Effects of a larval mosquito biopesticide and Culex larvae on a freshwater nanophytoplankton (Selenastrum capricornatum ) under axenic conditions

Abstract

The effects of microbial biopesticides used for mosquito control on autotrophic microorganisms such as nanophytoplankton are equivocal. We examined impacts of mosquito biopesticides and mosquito larvae on primary producers in two independent experiments. In the first experiment, we examined the effects of a commonly used microbial biopesticide formulation (VectoMax® CG) on a unicellular microalga, Selenastrum capricornatum Printz, under axenic laboratory conditions. The biopesticide treatments included two concentrations (0.008 and 0.016 g liter -1) of VectoMax® CG and two controls (one untreated and another with autoclaved 0.016 g VectoMax® CG liter -1 ) in replicated axenic experimental microcosms. Spectrophotometric analysis of chlorophyll a (proxy for algal biomass) and direct enumeration of algal cells following the treatments revealed no significant effects of the microbial biopesticide on algal population growth during the four-week study. In the second experiment, we tested the effects of different densities of Culex larvae on the population of S. capricornatum. Effects of mosquito larvae feeding on S. capricornatum were significant with a curvilinear relationship between larval density and algal abundance in the water column. Together, these studies demonstrated a lack of direct cytological/toxicological effects of Bacillus-based microbial pesticides on freshwater primary production and support the hypothesis that the reduction in algal primary production previously reported when Bti products were applied to aquatic environments was likely independent of the Bacillus-based larvicidal toxins. Instead, it was likely mediated by microbial interactions in the water column and the trophic cascade effects that resulted from the removal of larval mosquitoes. These studies suggest that mosquito larvae independent of pesticide application can influence primary production. Our method of evaluating biopesticides against small photoautotrophs can be very useful for studying the unintended effects on autotrophic microorganisms of other pesticides, including herbicides and pesticides applied to aquatic environments. Journal of Vector Ecology 42 (1): 51-59. 2017.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

“…It is worth noting that, in some scenarios, chironomides can also be a target species. Some initial assessments of the combined set of Bti and L. sphaericus crystals on non-targets organisms have also been investigated [ 316 , 317 ]. To date, Bin crystals and Bti crystals are still considered as safe compounds that effectively control several dipteran species larvae of medical importance.…”

Interactive effects of dragonfly larvae and Bacillus thuringiensis var. israelensis on mosquito oviposition and survival

“…Filter‐feeder microcrustaceans are known to decrease phytoplankton abundance in the absence of their predators (Kroeger et al, 2013). Although it is not their dominant food source (most Culex mosquito larvae filter organic matter and associated microorganisms), certain filter‐feeding mosquito larvae such as Culex and Anopheles are also known to depress the abundance of phytoplankton (Duguma et al, 2016; Gimnig et al, 2002; Kaufman et al, 2006). Even without direct consumption—mosquito larvae eat fine organic particles and associated microbes—they may still reduce algal biomass because they assimilate nutrients that otherwise could be used by phytoplankton, but this is speculative.…”

The ecological significance of arthropod vectors of plant, animal, and human pathogens

“…The larvae of most vectors of human and animal pathogens feed on primary producer microorganisms (bacteria, protozoans, rotifers, diatoms and algae) and organic waste in either aquatic (mosquitoes, blackflies) or humid terrestrial (midges, sandflies) environments [39]. Arthropod vectors may structure the community of these microorganisms and influence processes such as the decomposition of organic detritus and water purification in complex ways [40]. For example, a reduction in mosquito density can increase natural protozoan richness and abundance in Swedish wetlands [41], or alter the bacterial community in experimental microcosms [42].…”