Bee sensitivity derived from acute contact tests biased by standardised protocols?

In an acute contact test with bees the compound of interest is dissolved in a carrier solvent (frequently acetone) and then a droplet of the solution is placed on the dorsal thorax of the bee. The volume of the droplet is standardised to 1 µL for honeybees and to 2 µL for bumblebees. In practice the same droplet volume is used for bees with very different sizes. In this research the effect of the droplet volume was evaluated with acute contact tests with dimethoate for the alfalfa leafcutter bee, the red mason bee, the honeybee and the bumblebee. The results were analysed with a ToxicoKinetic ToxicoDynamic (TKTD) model to separate kinetic from dynamic effects. This allows to compare the sensitivity of the bee based on the effect threshold and not on the time, species and test dependent LD50s. The analysis of the test results indicates that the magnitude of the response of the bees increased with increasing droplet size. The results also showed that the manifestation of effects over time is slower for the red mason bee and the bumblebee compared to the honeybee and the alfalfa leafcutter bee. This implies that the result of a 2 day test with a fixed dosing volume results in different response for a bumblebee compared to the alfalfa leafcutter bee, not because of different sensitivities of the bees involved but due to the difference of relative dosed surface ratio. So comparing the sensitivity of bee species, based on standardised tests is biased and amplifies the sensitivity for the smaller bee species.

Appropriate larval food quality and quantity for Aedes albopictus (Diptera: Culicidae).

The Asian tiger mosquito Aedes albopictus (Skuse, 1894) is a globally invasive prominent vector of viral and parasitic pathogens. To soundly guide insecticide use in control programs it is crucial to use standardized test systems under rigorously controlled environmental conditions that allow for comparisons across laboratories. An acute standard test procedure (24 h) for insecticide resistance monitoring of mosquitoes has been published by the World Health Organization in 1998, but a standardized chronic test to monitor sublethal insecticide effects on the life cycle of mosquitoes does not yet exist. As a first step toward a standardized chronic bioassay (half-life-cycle-test), the exclusion of qualitative and quantitative food effects by means of standardized, optimal larval feeding would greatly facilitate inter-laboratory comparisons. Against this background we evaluated food qualities and quantities for the aquatic part of the A. albopictus life cycle under different thermal conditions. Five mg TetraMin (Tetra, Melle, Germany) larva(-1) at 25 degrees C rendered the lowest mortality and large pupae. Our fundamental data on A. albopictus feeding provide an opportunity to standardize experiments and thus support interlaboratory comparisons of studies on the ecotoxicology of this dangerous vector mosquito.

Larval superiority of Culex pipiens to Aedes albopictus in a replacement series experiment: prospects for coexistence in Germany.

BACKGROUND: The Asian tiger mosquito Aedes albopictus is an extremely invasive, globally distributed and medically important vector of various human and veterinary pathogens. In Germany, where this species was recently introduced, its establishment may become modulated by interspecific competition from autochthonous mosquito species, especially Culex pipiens (s.l.). While competitive superiority of Ae. albopictus to Cx. pipiens (s.l.) has been described elsewhere, it has not been assessed in the epidemiological conditions of Germany. The present study aimed to determine if such superiority exists under the physicochemical and microclimatic conditions typical for container habitats in Germany. METHODS: In a replacement series experiment, the larval and pupal responses of Ae. albopictus and Cx. pipiens (s.l.) (mortality, development time, growth) to interspecific interaction (five larval ratios) at (sub-)optimal temperatures (15, 20 and 25 °C) and differing food supply (3 and 6 mg animal-based food larva-1) were investigated using a randomized split-plot design. In addition to physicochemical measurements of the test media, natural physicochemical conditions were determined for comparative analyses in mosquito breeding sites across the Rhine-Main metropolitan region of Germany. RESULTS: Under the physicochemical and microclimatic conditions similar to the breeding sites of the Rhine-Main region, competitive superiority of Cx. pipiens (s.l.) to Ae. albopictus in terms of larval survival was more frequently observed than balanced coexistence. Food regime and multifactorial interactions, but not temperature alone, were controlling factors for interspecific competition. Larval food regime and the larval ratio of Ae. albopictus influenced the physicochemistry and algal growth at 15 °C, with increased Ae. albopictus mortality linked to a decreasing number of Scenedesmus, Oocystis and Anabaena algae. CONCLUSIONS: Under the present environmental conditions, the spread of Ae. albopictus from isolated foci in Germany may generally be slowed by biotic interactions with the ubiquitous Cx. pipiens (s.l.) (and potentially other container-breeding mosquito species) and by limnic microalgae in microhabitats with high resource levels. Detailed knowledge of the context dependency in temperate mosquito ecology, and interrelations of physicochemistry and phycology may help to achieve a better understanding of the upcoming Ae. albopictus colonization processes in central and northern Europe.