Ecological effects of experimental insecticide applications on invertebrates in sahelian temporary ponds

Abstract

Abstract-The ecological impact of four insecticides used to control desert locusts was investigated during experimental field trials in natural temporary ponds in a cultivated savannah area of Senegal, West Africa. The insecticide formulations, dose rates, and application techniques were similar to those used in operational desert locust control. Average initial concentrations of fenitrothion, diflubenzuron, deltamethrin, and bendiocarb in pond water were 80, 10.4, 0.45, and 24.0 g/L, respectively. Diflubenzuron and deltamethrin virtually disappeared in 24 h. Pseudo-first-order half-lives were 34 h for fenitrothion and 17 d for bendiocarb. Fenitrothion and deltamethrin significantly reduced population densities of backswimmers of the genus Anisops (Hemiptera, Notonectidae) and in addition caused an extensive kill of other species of insects. Both insecticide applications were also followed by reductions of zooplankton densities, especially Cladocera, and deltamethrin eradicated populations of fairy shrimp (Streptocephalus spp.: Branchiopoda, Anostraca). Diflubenzuron only affected crustaceans, i.e., cladocerans and fairy shrimp. The least harmful insecticide in the study was bendiocarb, which only reduced the density of cladocerans. Recovery proceeded at fixed rates, which were different for each taxon. Anisops spp. recovered from the treatments in 1 to 4 weeks, most likely through aerial migration. Cladocerans returned to normal densities in 3 to 6 weeks. Streptocephalus spp., however, whose resting eggs presumably need desiccation during the dry season to be able to hatch, did not reappear until the next rainy season, one year later. It is concluded that contamination of temporary ponds in the Sahel by insecticide drift from desert locust control operations with any of the four insecticides should be avoided.

Threshold Levels for Effects of Insecticides in Freshwater Ecosystems: A Review

“…Testing pesticides in outdoor (model) ecosystems has the advantage that this type of research may provide information on the recovery of the systems after pesticide contamination has ceased. Actual recovery of sensitive populations depends on the instant that concentrations reach non-toxic levels again, in combination with an array of biological and ecological characteristics (e.g., Giesy et al, 1999;Brock and Budde, 1994;Lahr et al, 2000). The microcosm and mesocosm studies demonstrate that recovery after pesticide contamination is expected to be rapid in the real world when (a) the compound is not persistent, (b) the physicochemical environment is not altered, or is quickly restored, (c) the generation times of vulnerable populations are short, and/or (d) when there is immigration from residual populations in nearby unaffected areas.…”

Pyrethroid Insecticides: Use, Environmental Fate, and Ecotoxicology

“…Deltamethrin applications to temporary ponds located in the savannahs of West Senegal had immediate and catastrophic, but largely short-term effects, on the resident aquatic invertebrates. Significant numbers of moribund insects were evident during insecticide application, and these were largely predatory hemipterans and coleopterans (Lahr et al, 2000). Conversely, direct applications of cypermethrin at 0.7 g a.i./ha and lambdacyhalothrin at 0.17 and 1.7 g a.i./ha produced no effect on the composition of emergent insect communities in mesocosm pond systems (Kedwards et al, 1999).…”

Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides

“…Dissipation rates of alachlor, atrazine, endosulfan, metalochlor, profenofos, simazine and trifluralin in outdoor aquatic microcosms set up in Brazil were not distinctively greater in comparison to temperate (semi-) field or laboratory studies (Laabs et al 2007). Lahr et al (2000) concluded that, given the results from laboratory studies, bendiocarb and fenitrothion were surprisingly persistent in tropical experimental ponds in the Sahel. As described above, DT50 values of chlorpyrifos determined in the laboratory decrease considerably with temperature ( Fig.…”

“…Several reasons for the absence of faster disappearance rates under tropical conditions have been distinguished, and include: (1) decreased photolysis due to turbid water conditions in the tropics (Lahr et al 2000;Fig. 2); (2) inclusion of pesticide residues adsorbed to (high concentrations of) suspended matter, i.e., algae and other particles, in combination with low organic content of the sediment and hence a smaller ''disappearance'' to this compartment (Lahr et al 2000;Daam et al 2008); (3) differences in prevailing pH regime (Zulkifli et al 1983;Lahr et al 2000;Mehetre et al 2003); (4) influence of dimensions of the (model) ecosystem, e.g., depth (Laabs et al 2007;Daam et al 2008). Although Laabs et al (2007) did not observe a faster dissipation of the pesticides mentioned above in the tropical aqueous environment, Laabs et al (2002) demonstrated substantial fate differences between tropical and temperate soils.…”

“…Caridina africana, one of the most widespread shrimp species in inter-tropical Africa, was found to be considerably more sensitive to the larvicide etofenprox than Oreochromis niloticus and Tilapia zilli (Yaméogo et al 2001). The fairy shrimp Streptocephalus sudanicus was concluded to be important in evaluating possible effects of insecticides on temporary ponds in the Sahel because they are very typical for this habitat, differed highly in their response to insecticides compared to Daphnia magna and recovered extremely slow compared to many other invertebrate groups (Lahr et al 2000(Lahr et al , 2001.…”