By Brandon Gillet
A City of Ottawa mosquito-control project that uses a naturally occurring insecticide to starve larvae is being monitored by a uOttawa professor for its potential impact on other bugs.
Two months ago, the city began to use Bti (Bacillus thuringiensis israelensis), a bacteria, to kill off mosquitoes near Kanata. This bacteria produces a protein that disrupts the gut of mosquito larvae.
Residents living around Kizell Pond and elsewhere in Kanata North had complained that they were being eaten alive and couldn’t enjoy the outdoors. They voted to pay an average annual levy of $20 for four years to cover the cost of the project — and the uOttawa study.
“The city insisted on impact studies, so we will be looking at other species of related insects and comparing emergence patterns of treated and control ponds in the area,” said Professor Antoine Morin of the Department of Biology.
Kanata was developed around wetlands, so mosquitoes were to be expected, he said. “But when mosquitoes are in abundance, it’s not fun for anyone. There can be health concerns, such as West Nile Virus, so you don’t want to be exposed.”
Over the next three years, Morin will study the impact of Bti and mosquito removal on the wetlands of Kanata North. His student Liam Epp, who plans to do a master’s degree on the subject, will handle the field work.
“On a weekly basis, I visit 29 ponds where we have strategically placed traps to capture adult aquatic insects as they emerge from the water,” Epp said.
Of the tested sites, 14 are in the Bti treatment area and 15 sites are in similar habitats that are not being treated.
“The abundance of insect species can be used to assess the selectivity of the Bti treatment,” Epp said. “We would like to resolve whether Bti has an impact on the biodiversity and community structure in the Kanata wetlands.”
The City of Ottawa says Bti has no effect on humans, birds, fish and amphibians, and is not toxic to other insects at the dosage used.
However, Morin says the protein, which is found naturally in soils where the bacteria live, could attack the digestive systems of other members of the insect order Diptera, such as flies, gnats and midges. While mosquitoes are minor players in most ecosystems, those other species could be more important.
“There isn’t much concern, as Bti has been used and studied worldwide,” Morin said. “But when you manipulate nature, you will have some sort of effect.” The study will not examine the impact on animals that feed on mosquitoes, such as bats, birds and frogs. Morin believes those species don’t rely solely on mosquitoes and could easily substitute something else in their diet.
“This insistence by the City to have an impact study is a win-win-win,” Morin said. “A uOttawa student gets a funded research project, the city and its citizens gain useful data pertaining to the ecosystem in the area and are being responsible for the environment, and GDG Environnement, the company hired to spray Bti, gets more publicity and credibility.”
So what happens when mosquitoes are decimated with Bti? Not much at first, Morin says, but there could be indirect effects not seen right away. That’s why the study will also be examining the other bacteria that could react to nitrogen levels, which would increase as mosquito larvae die.
“There’s a good possibility other species will replace mosquitoes in the diet of predators, but no one really knows which ones because it’s different in every place and every year,” Morin said. And if the impact is found to be larger than expected, it is likely reversible. “If they stopped using the Bti, for whatever reason, remaining eggs in the sediments or migrating mosquitoes from around will quickly recolonize.”