INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Impact of Different Bacillus thuringiensis Variety israelensis Treatments on a Chironomid (Diptera Chironomidae) Community in a Temporary Marsh D. PONT, 1 E. FRANQUET, 2 AND J. N. TOURENQ 3 J. Econ. Entomol. 92(2): 266Ð272 (1999) ABSTRACT Bacillus thuringiensis variety israelensis is a selective biological insecticide for control of mosquito and black ßy larvae and has little or no effect on nontarget organisms. Its impact on the structure of lentic communities, however, has rarely been tested in the Þeld. Chironomid larvae were sampled in a control zone (0 mg B. thuringiensis/liter) and in a treated enclosure (1.6 mg/liter) on 5 sampling dates. The emergence of adults also was studied at 4 treatmentsÑ 0, 1.6, 3.3, and 6.7 mg/liter. One week after treatment with 1.6 mg B. thuringiensis/liter, chironomid larval density decreased by 38%. Treatment with B. thuringiensis affected the emergence of sampled chironomids. Ten days after treatment, Polypedilum nubifer (Skuse) was the only sampled organism which increased in relative abundance. P. nubifer represented 75% of the emerging adults. KEY WORDS Bacillus thuringiensis variety israelensis, nontarget insects, Chironomidae, commu- nity, toxicity, lentic waters TEMPORARY SHALLOW MARSHES provide habitat for the larval development of many species of biting midges. In the French Mediterranean littoral zone, mosquitoes are an important public nuisance. For 25 yr, the En- tente Interde ´ partementale pour la De ´ moustication (EID) has treated lentic waterbodies of this area with temephos (Abate), an organophosphate insecticide. However, this insecticide kills some nontarget inver- tebrates (Yap et al. 1982), including chironomids (Ali et al. 1985, Sine ` gre et al. 1990, Ali et al. 1992, Ali 1996), which may be one of the most important components of freshwater ecosystems (Pinder 1986). Chironomids are important elements of trophic webs (Lugthart et al. 1990), in particular as Þsh prey (Berg and Hel- lenthal 1993), and in organic matter turnover (Benke et al. 1984) and puriÞcation processes in freshwater ecosystems (Lugthart et al. 1990). They are an impor- tant part of biodiversity. In the protected natural area of the Camargue Rho ˆ ne Delta, chironomids constitute a large propor- tion of community biomass (Tourenq 1976). The use of a nonspeciÞc insecticide against mosquitoes could harm chironomid fauna and others and indirectly af- fect the ichthyofauna and the avifauna of the area. One alternative is to use a more speciÞc larvicide such as Bacillus thuringiensis var. israelensis serotype H 14 (Barjac 1978). The B. t. variety israelensis bacterium forms crystal proteins that are activated in the diges- tive tract of some invertebrates. In contrast with exo- toxins, the mode of action of these crystal proteins is highly speciÞc (Honee and Visser 1993). This biolog- ical insecticide is effectively used against simuliid lar- vae in lotic systems (Merritt et al. 1989, Jackson et al. 1994) and against mosquitoes in stagnant water (Mulla et al. 1982, Charbonneau et al. 1994). Studies have shown that B. thuringiensis is safe for nontarget aquatic fauna (Merritt et al. 1991, Molloy 1992, Wipßi and Merritt 1994). Numerous studies have tested the im- pact of B. thuringiensis against individual chironomid species (Ali et al. 1985, Sine ` gre et al. 1990, Kondo et al. 1992, Charbonneau et al. 1994), but the impact against an entire community has not been recorded. The objective of this study was to determine if applications of B. t. variety israelensis (1.6 mg/liter) for mosquito control has an impact on the densities of chironomid larvae. Also, we wanted to examine the impact of 2 higher doses of B. thuringiensis on the emergence of different species and its effect on the structure of a faunistic assemblage. Materials and Methods Study Site. The study site was a temporary shallow oligohaline marsh which is primarily managed for wa- terfowl and pasture. This marsh was artiÞcially ßooded (irrigation water input) 22 d before our experiments (20 June to 4 July) to allow a sufÞcient colonization by macroinvertebrates. Vegetation was dominated by Scirpus maritimus Linne ´ and Salsola soda Linne ´ , but with a highly variable vegetation cover. Within the marsh, the experimental area was enclosed with a 1 Ecologie des Eaux Douces et des Grands Fleuves, CNRS-ESA 5023 (Universite ´ Lyon1), 43 bd du 11 Novembre 1918, 69622 Villeurbanne Cedex, France. 2 Laboratoire dÕEcologie des Eaux Continentales Me ´ diterra- ne ´ ennes, CNRS-ESA 6034 Universite ´ Aix-Marseille III, Avenue Es- cadrille Normandie - Niemen, case 331, 13397 Marseille Cedex 20, France. 3 Centre dÕEcologie des Syste ` mes Aquatiques Continentaux, CNRS-UMR 5576 (Universite ´ P. Sabatier), 118 route de Narbonne, 31062 Toulouse Cedex, France. 0022-0493/99/0266Ð0272$02.00/0  1999 Entomological Society of America Downloaded from https://academic.oup.com/jee/article/92/2/266/2216987 by guest on 22 July 2022