Environmental effects of mosquito insecticides on saltmarsh invertebrate fauna

Despite the fact that Bacillus thuringiensis var. israelensis de Barjac (Bti) and s-methoprene are considered to be among the most target-specific of insecticides, there are some indications that non-target organisms may be impacted in different ecosystems. We examined the effects of Bti and s-methoprene on non-target aquatic and terrestrial fauna in 2 subtropical saltmarshes approximately 30 km apart. The main taxa collected from ephemeral pools were copepods and from terrestrial plots were springtails (Collembola), mites (Acariformes) and ants (Hymenoptera), with smaller numbers of beetles (Coleoptera), true bugs (Heteroptera) and flies (Diptera). Following applications of both products, inconsistent short-term (<20 d) differences in the composition of the arthropod community were noted. After applications of Bti to ephemeral pools, smaller numbers of copepods were recorded but at only one locality. There were no significant effects of s-methoprene on the arthropods in ephemeral pools at either locality. The numbers of mites increased in terrestrial plots after applications of s-methoprene at both localities and Bti at one locality, but these effects were short-lived and varied depending on which specific habitat was sampled (i.e. vegetation or sediment surface). There were few significant effects on any other taxa and these effects were also localised and short-lived. These results suggest that applications of Bti and s-methoprene do not impact the abundance and composition of non-target arthropod assemblages in subtropical saltmarshes, although more work on potential sub-lethal effects of the insecticides is needed. © Inter-Research 2009.