A new invasive weevil that is turning berry buds into duds in British Columbia
By Michelle Franklin, Paul Abram, and Tracy Hueppelsheuser
Most of the weevils we find in raspberry and strawberry fields in the Fraser Valley of British Columbia (BC) are nocturnal, so you would be hard pressed to find adult weevils without venturing out at night with your headlamp or flashlight. However, in 2019 a curious small black weevil was observed during the day in a backyard raspberry patch in Abbotsford, BC.
The first specimens of this weevil were collected by Provincial Entomologist and coauthor, Tracy Hueppelsheuser from the BC Ministry of Agriculture, Food and Fisheries and sent to taxonomists and co-authors, Dr. Patrice Bouchard from the Canadian National Collection and Dr. Robert Anderson from the Canadian Museum of Nature for their expert identification. It turned out that this weevil was indeed new to the Fraser Valley, BC. This tiny (2.5 – 3mm), black, long nosed weevil was the strawberry blossom weevil, Anthonomus rubi, which is native to Europe, Asia, and North Africa. This was the first observation of this species in North America.
Strawberry blossom weevil is not just a pest of strawberries. It is able to feed and reproduce on a wide variety of plants in the family Rosaceae, including other economically important berry crops such as raspberries and blackberries. Adult weevils overwinter in the leaf litter and become active in the spring. After mating, the female chews a hole inside a closed flower bud, lays her egg inside, and then clips the stem below, killing the bud and preventing fruit development. The weevil larva then develops inside the bud and emerges as an adult about a month later when temperatures are warm in the summer. In its native range, the weevil completes a single generation each year.
I started my position as a research scientist in July 2020, specializing in small fruit entomology and Integrated Pest Management at the Agassiz Research and Development Centre of Agriculture and Agri-Food Canada. With help from Paul Abram (Agriculture and Agri-Food Canada), Tracy Hueppelsheuser (BC Ministry of Agriculture, Food and Fisheries), and crop consulting company, ES Cropconsult we hit the ground running, completing surveys in the Fraser Valley in the summer 2020 to determine the distribution and associated host plants of the strawberry blossom weevil. We found adult weevils on cultivated plants (e.g. strawberry, raspberry, blackberry, and rose) and wild hosts (e.g. salmonberry, thimbleberry, Himalayan blackberry, and wild rose). Our survey found this species to be well established throughout the Fraser Valley from Richmond to Hope.
However, there is some good news for potential natural pest control. Later during the summer we saw parasitoid wasps around weevil-damaged Himalayan blackberry buds. We knew that some species of parasitoid wasps had the potential to be natural enemies of the weevil. Parasitoid wasps lay eggs on weevil larvae and their offspring often develop on the larvae resulting in their death. This behaviour has been successfully used as biological control of other weevil pests for decades. Hence, we initiated natural enemy surveys by collecting damaged buds from the field. Although COVID protocols restricted lab access, I monitored damaged buds in my temporary laboratory (a.k.a home garage) and within a few weeks parasitoids emerged! Over the summer, we had over 150 parasitoids emerge from strawberry blossom weevil damaged buds. With the help of taxonomist and co-author, Dr. Gary Gibson from the Canadian National Collection, we identified the metallic-colored parasitoid to the genus Pteromalus. Future work is needed to identify the parasitoid to the species level, determine its origin (native to North America or inadvertently introduced from another continent), and determine its impact on strawberry blossom weevil populations.
I am continuing to work with my co-authors to understand the biology of this new pest and its natural enemies, with the goal of using this knowledge to develop sustainable pest management strategies in the future. If you are interested in this new berry pest, please contact me at email@example.com.
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Full article: https://doi.org/10.4039/tce.2021.28