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(12-04) Combined use of individual biomarkers and community indices to assess the impact of chemical mosquito control in non-target invertebrates from coastal wetlands of Morbihan (Brittany, France). Lagadic, Laurent*,1, Caquet, Thierry1, Fourcy, Damien1, Jumel, Audrey1, Heydorff, Micheline1, 1 INRA, Rennes, France ABSTRACT- Since 1998, a pilot study has been undertaken to evaluate the ecological impact of Abate® 500e (a.i. temephos) and Vectobac® 12AS (a.i. endotoxin of Bacillus thuringiensis var. israelensis, Bti) used against mosquito larvae in Morbihan coastal wetlands. Three study sites were chosen, and control and treated areas were delimited in each site. The midge Chironomus salinarius and the marine worm Nereis (Hediste) diversicolor were used as sentinel species, and in situ exposure was monitored using acetylcholinesterase (AChE) and carboxylesterase (CbE) activities. Sentinel organims were isolated from sediment samples (4.5 L) collected in both control and treated areas 24 and 72 hours after larvicide spraying. Pools of 3 to 5 entire fourth instar midge larvae were used for both AChE and CbE assays. For N. diversicolor, extracts were prepared from the head and rest of the body for AChE and CbE assays, respectively. As compared to the controls, temephos-exposed animals regularly showed inhibited AChE and CbE activities. In N. diversicolor sampled in Bti-sprayed areas, random variations of esterase activities were observed, that could not be attributed to the larvicide. In contrast, inhibition of esterases were observed in Bti-exposed midge larvae. Connection with potential effects at higher levels of biological organisation was assessed through the use of macroinvertebrate community indices. Invertebrate community sampling was performed every 7 weeks in the control and treated areas of each site. A 25 cm diameter corer was used to collect benthic and pelagic invertebrates, which were identified to the most readily accessible taxonomic level (usually family) and enumerated. Taxonomic abundance data were used to compute taxonomic richness, Shannon′s diversity index and Simpson′s dominance index. Similarity between control and treated areas was evaluated using Bray-Curtis′index. Abundance of different feeding groups was used to determine functional diversity in each area and similarity between control and treated areas in a same site. The results suggest that Bti may have a significant impact on similarity between control and treated areas, whereas no effects of temephos were detected. Key words: mosquito control, organophophate, biological insecticide, non-target invertebrates |
