Production of wetland Chironomidae (Diptera) and the effects of using Bacillus thuringiensis israelensis for mosquito control

Abstract

Massive mosquito nuisance problems, caused by the flood-water mosquito Aedes sticticus, occur after floods in the flood plains of the River Dalälven, central Sweden. Since 2002, the biological mosquito larvicide Bacillus thuringiensis var. israelensis (Bti) has been used to control these mosquitoes. Here, we report results from the first six years of monitoring Chironomidae, the most susceptible nontarget organisms, in three wetlands with Bti-treatment against mosquitoes and in three wetlands without treatment. Emergence traps were used for continuous insect sampling from May to September each year, 2002-2007, and were emptied once a week. A total of 21,394 chironomids of 135 species were collected, and the subfamily Orthocladiinae dominated the fauna followed by Chironominae and Tanypodinae. The annual chironomid production in the wetlands was low, with an average of 1917 individuals per m 2 , and 42 g ash-free dry weight per m 2 . We found no reduced production of chironomids at neither family, nor subfamily level, in Bti-treated as compared to untreated wetlands. This is the first long-term follow-up study of the possible effects of Bti-based mosquito larval control on chironomid species production. In the short-term view, one species had higher production in treated areas. In the long-term view, four species had higher and one species had lower production in treated areas. We conclude that the Bti-based control of floodwater mosquitoes does not cause any major direct negative effects on chironomid production, and therefore does not seem to induce any risk for indirect negative effects on birds, bats or any other predators feeding on chironomids.

Using DNA metabarcoding for assessing chironomid diversity and community change in mosquito controlled temporary wetlands

“…Especially first instar larvae of C. riparius were shown to be highly affected by Bti in laboratory experiments while older larvae were less sensitive (Kästel et al 2017). Until WAA 13 there was a non-significant trend towards more chironomids in the Bti-treated sites, which could be due to a reduced mosquito competition (Lundström et al 2010) and subsequently chironomids with a second reproductive cycle in the same year had better conditions (more food resources available) to reproduce. Moreover, species have different egg laying and hatching times, and Bti does not affect eggs but only hatched individuals (Boisvert and Boisvert 2000).…”

“…So far, field studies have yielded ambiguous data on possible side effects of Bti on chironomid abundances. These range from positive effects on chironomid larvae richness possibly due to reduced mosquito competition (Lundström et al 2010), over no effect on chironomid abundance (Lagadic et al 2016), to a 35-80% reduction of chironomids abundances (Rodcharoen et al 1991, Hershey et al 1995, Vaughan et al 2008, Poulin et al 2010, Jakob and Poulin 2016.…”

Chironomidae of semiaquatic lake shore habitats in the Karelian Isthmus (northwestern Russia)

“…(e.g. Crisp & Lloyd 1954;Pankratova 1954;Hudson 1987;Wrubleski 1987;Lundström et al 2009aLundström et al , 2009bEkrem et al 2010).…”

“…In northern Europe, the emergence of Chironomidae from semiaquatic habitats was studied only by few researchers (Paasivirta et al 1988;Paasivirta 2007;Przhiboro 2008;Lundström et al 2009aLundström et al , 2009bEkrem et al 2010). Chironomid immatures were rarely sampled quantitatively in these habitats as well.…”

Diving beetle assemblages of flooded wetlands in relation to time, wetland type and Bti-based mosquito control

“…israelensis (Bti) as active ingredient, to reduce populations of Aedes sticticus and other flood-water mosquito species. Bti is specific and efficient against mosquitoes (Becker et al, 2003) with few or no direct negative effects on non-target insects (Boisvert & Boisvert, 2000;Lundström et al, 2009). Flood-water mosquito larvae are abundant in the flooded areas from about 24 hours after the flood reaches its maximum level, and for about 10 days depending on the water temperature.…”