Maine still has low populations of budworm in 2016

BUDWORM IN BRIEF: Maine’s trap numbers, the L2 data and ground and air observations all confirm we are still in a period with low populations of spruce budworm across Maine’s forests. (See Spruce Budworm 2016 Report)

allison-column-sigIn 2016, Quebec reported a total of 17.3 million acres have been defoliated by spruce budworm, a slight increase from 2015. That’s nearly as much as all Maine’s forestland, which totals 17.8 million acres. Quebec has seen defoliation every year since 2003 and the province’s budworm epidemic has increased significantly since 2009. 

Since 2015, defoliation has roughly doubled in the area down river from Riviere-du-Loup along the St. Lawrence. Maine is downwind of the defoliation in this region, which is less than 30 miles from our heavily forested, host-rich border. 

Although Maine has been monitoring budworm populations using pheromone traps since the early 1990s, the state increased its effort in the spring of 2014. Charlene Donahue of the Maine Forest Service took on the task of recruiting and coordinating the involvement of additional partners across the region impacted. Since 2014, about 20 partners helped augment the trap network across the state, dedicating their resources for planning and carrying out surveys for adult male budworm moths. Although this is a big program to manage, the information that comes from it is very valuable.    

Click for larger image.

In 2016, we had about 420 sites in the cooperator network with the average catch per trap around seven moths. This was down significantly from 2015, when the average was about 26 moths per trap across all sites. We don’t have a pre-outbreak record of pheromone trap catches, but our light trap records show similar valleys and peaks both during the build-up to outbreak and within the outbreak itself.

Comparing geographic patterns year to year, we can see the same “hot spots” show up (and these catches are too low to really indicate a hot spot). This year the most moths caught per trap at a site has been 49, while last year we had 320 at one site, and several sites over 150 moths/trap. The sites with higher catches this year, 20-50 per trap, were in similar locations to the higher catches last year. 

Looking at those per trap averages another way over the last 3 years the proportion of traps catching >1 to 50 moths has dominated the field. We still have very low populations across the state and we have not seen defoliation from the ground or in aerial survey.

Click for larger image.

Maine is not alone in seeing decreased numbers of budworm moths in traps. New Brunswick catches were also down for the most part. With similar numbers cross border in most locations. The only catch over 100 outside of the area already experiencing defoliation was found in central western New Brunswick and was not reflected in catches seen here in Maine. 

There also is another new network of cooperators monitoring pheromone traps. Volunteers from the public have signed up for the Healthy Forest Partnership’s Budworm Tracker Program, which is coordinated by Emily Owens from the Canadian Forest Service. She had 37 sites signed up in Maine in 2016. 

At these sites volunteers agreed to track catches in a pheromone trap on either a weekly or more frequent basis. This will help researchers tease out flights of migrant moths vs. local moths and contribute to a better understanding of both the monitoring tool and spruce budworm dynamics. 

We had a nice scatter of sites in Maine, but hope to fill in some of the unmonitored areas in northwestern Maine in the second year of the program using cooperators who live part time and/or work in that area.  We are grateful for Maine’s citizens’ commitment to helping to monitor the state’s forest health. 

The University of Maine Cooperative Forest Research Unit also is coordinating an L2 survey (in which the second instar larvae are collected from the branches), which tracks overwintering spruce budworm to help predict the following years’ populations. Samples were collected by many of the same organizations cooperating in the pheromone trap network, and were processed by New Brunswick’s Forest Health Lab in Fredericton. These, more than moths in pheromone traps, track the local pressure from spruce budworm. 

Click here for larger image.

The samples from last winter yielded 14 positive sites out of approximately 245 sampled. All but one of those sites had fewer than 3 larvae per branch (very low populations).  All positive sites were in areas from Houlton north. It is great to have a look at L2 populations at this stage of the spruce budworm populations and we really appreciate CFRU and its cooperators taking it on. 

Although our moth catches did not build over last year’s, we can still expect to see defoliation on a similar timeline, sometime in the next several years we expect to find defoliation caused by spruce budworm in Maine.  Even after that is found it will be several years before fir and spruce in Maine experience significant impacts to their growth. Managers and landowners with significant host-resource should use the time they have to continue to prepare for the coming epidemic.