Mass dispersal

Posted on May 01 2017

For many people, the mention of an “insect plague” brings to mind unnerving thoughts of massive locust swarms sweeping like a storm across the land to devour all crops and vegetation. Of course, locust outbreaks aren’t much of an issue for Canadians – but, we do have our own version of an “insect plague” looking to sweep through our region. On several cloudless evenings from July 20 through 25, 2016, weather radar detected moving plumes of spruce budworm moths coming from Quebec into New Brunswick (Fig. 1). Moths are attracted to bright lights, and as a result, these plumes tended to descend upon well-lit areas. In the aftermath we were left with many concerning images of parking lots and cars covered in dense carpets of fluttering moths, especially in areas to the north of New Brunswick such as Campbellton (Fig. 2).

Trillions of budworm moths were estimated to have dispersed during this mass dispersal event. Certainly the sheer spectacle and aftermath garnered a fairly high level of public interest and media coverage. Yet, although the event was certainly striking in its imagery it was the practical implications of the event that raised the most concerns: Could these mass dispersal events completely overwhelm our ongoing efforts to slow the spread of budworm through Atlantic Canada (i.e., the Early Intervention Strategy project)?

A large part of our effort during the late summer was focused on this question – so, what did we learn? First of all, with the help of our dedicated citizen scientists (Budworm Trackers: we determined that the dispersal event was likely quite extensive, perhaps reaching as far as Cape Breton and deep into Maine, USA. From the moths we scooped up from parking lots and from around trees in Campbellton (Fig. 3), we discovered that nearly 80% of the moths were females, potentially carrying as many as 180-200 eggs each! However, on-the-ground surveys conducted immediately after the event suggested that high densities of eggs were laid mainly in the area within 30-50 km of Campbellton, though there was evidence of some sparse egg deposits reaching as far as Nova Scotia.

From these results we were able to draw a few tentative conclusions. Even with the impressive scale of the mass dispersal event our evidence to date suggests that whatever impact it had was fairly local to northern New Brunswick, where densities rose somewhat this past summer. This invasion is thus quite manageable under the framework of the Early Intervention Strategy, which allows for some moth dispersal from Quebec. Nonetheless, two questions remain to be answered: (1) Are the deposited budworm able to overcome local controls (e.g., bird and insect predators) to ultimately become new ‘hot spots’? (2) Can treating these growing ‘hot spots’ with insecticide (Btk or tebufenozide) keep them from further expanding the outbreak? Research this year will address these and other questions as we continue our ongoing research to understand how budworm outbreaks advance over the landscape and whether we might be able to slow its spread.

Rob Johns

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