Population-level effects of spinosad and Bacillus thuringiensis israelensis in Daphnia pulex and Daphnia magna: comparison of laboratory and field microcosm exposure conditions

Abstract

Because exposure to toxicants not only results in mortality but also in multiple sublethal effects, the use of life-table data appears particularly suitable to assess global effects on exposed populations. The present study uses a life table response approach to assess population-level effects of two insecticides used against mosquito larvae, spinosad (8 μg/l) and Bacillus thuringiensis var. israelensis (Bti, 0.5 μl/l), on two non target species, Daphnia pulex and Daphnia magna (Crustacea: Cladocera), under laboratory versus field microcosms conditions. Population growth rates were inferred from life table data and Leslie matrices under a model with resource limitation (ceiling). These were further used to estimate population risks of extinction under each tested condition, using stochastic simulations. In laboratory conditions, analyses performed for each species confirmed the significant negative effect of spinosad on survival, mean time at death, and fecundity as compared to controls and Bti-treated groups; for both species, population growth rate λ was lower under exposure to spinosad. In field microcosms, 2 days after larvicide application, differences in population growth rates were observed between spinosad exposure conditions, and control and Bti exposure conditions. Simulations performed on spinosad-exposed organisms led to population extinction (minimum abundance = 0, extinction risk = 1), and this was extremely rapid (time to quasi-extinction = 4.1 one-week long steps, i.e. one month). Finally, D. magna was shown to be more sensitive than D. pulex to spinosad in the laboratory, and the effects were also detectable through field population demographic simulations.

Effects of predator cues and pesticide resistance on the toxicity of a (bio)pesticide mixture

“…Similar to the current results, these studies did not report a higher mortality in the Ace‐1R strain compared to the S‐Lab strain in the absence of pesticides or natural enemies . This suggests that costs of resistance may be sublethal and too subtle to detect under optimal laboratory conditions . This lack of observable costs of resistance in the absence of the pesticide has been observed in other insects, e.g .…”

Effects of Bacillus thuringiensis israelensis and spinosad on adult emergence of the non-biting midges Polypedilum nubifer (Skuse) and Tanytarsus curticornis Kieffer (Diptera: Chironomidae) in coastal wetlands

“…Natural populations of Daphnia pulex and Daphnia magna were dramatically reduced by the exposure to 8, 17 and 33 mg L À 1 spinosad. Although recovery was observed in D. pulex in the Atlantic wetlands (Duchet et al, 2008), population model forecasted quasi extinction after 43.9 weeks (Duchet et al, 2010b).…”

Pesticide‐mediated trophic cascade and an ecological trap for mosquitoes

“…Path diagrams with standardized coefficients for (A) 12 June, one week after treatment, and (B) 10 July, approximately one month after treatment. Laboratory tests and field studies have shown that Bti may be safe to the environment due to its selectivity (Mulla et al 1982, Barnes and Chapman 1998, Boisvert and Lacoursi ere 2004, Duchet et al 2010b. Thick arrows are those whose coefficients were significantly different from zero at the 0.05 level, based on z-tests.…”