Mosquito control along the river Dalälven can impact other species
A research study from Uppsala University is investigating how the pesticide Bti affects not only mosquitoes but the entire food web along the river Dalälven. Photo: Getty Images.
Mosquito control along the river Dalälven is deemed to have a limited direct impact on other insects. But it may have indirect effects on the area’s biodiversity.
Frank Johansson, Professor of Conservation Biology at the Department of Ecology and Genetics. Photo: Daniel Olsson
Mosquitoes are, to say the least, not the most welcome feature of a Swedish summer, and the Färnebofjärden bay area in northern Uppland counts as one of the areas in Sweden that is particularly afflicted. Since 2002, the biodegradable pesticide Bacillus thuringiensis israelensis (Bti) has been sprayed over the area to control them.
“It basically completely eradicates the mosquitoes,” says Frank Johansson, professor at the Department of Ecology and Genetics, who is researching how Bti is affecting other organisms in the area.
“The studies carried out thus far in the Färnebofjärden bay area show that the direct effect on aquatic insects is small. However, there may be indirect effects on the food web.”
A number of possible scenarios
One possible scenario is that populations of spiders and dragonflies, for example, decline. If mosquitoes, which are an important food source, disappear, birds and bats may eat more spiders and dragonflies. Another possible scenario is that the loss of mosquitoes leads to birds and bats eating more terrestrial insects, which can affect the entire food web.
“Of course the ideal scenario is that the food web is not changed at all. Thus far, we don’t know whether, and if so how, Bti affects the food web,” says Frank Johansson.
In Sweden, mosquitoes are controlled in this way only in this area, but in other European countries this means of control is more common. Frank Johansson’s study is the first to investigate how Bti affects all actors in the food web.
“We started last summer. A group of field assistants went out regularly to empty insect traps, count insects, birds and bats, and collect scat samples from these species. We expect to see preliminary results in just over a year,” he says.
DNA analysed
A method called DNA barcoding is used, which means that the insects caught in the traps are ground down and run through an advanced machine that shows exactly which species there are and their prevalence. In addition, scat samples from birds, bats, dragonflies and spiders are analysed to determine who eats who.
“Parts of the sprayed area are compared to areas that are not sprayed. It’s lucky for us that those who manage the mosquito control do the groundwork for us. It would have been difficult otherwise to get permission to spray this pesticide ourselves for the purposes of our study,” says Frank Johansson.
Within the Area of Advance Evolution and biodiversity in a changing world, he is one of several researchers seeking answers to the decline in biodiversity that we are seeing today.
“The decline in insects is probably in part due to the use of pesticides. We also need to find out what indirect effects a biodegradable pesticide like Bti can have,” says Frank Johansson.
Sigrid Asker