And Another Destructive Weevil Species...

Published: February 5, 2021

Anthonomus rubi, is a weevil species that feeds on strawberry, raspberry, and blackberry blossoms and foliage. Known as the strawberry blossom weevil, this insect is a major pest across Europe to China. However, this weevil was recently identified in the Fraser Valley and in Vancouver, British Columbia in 2020 and is likely present in the United States. While the blossom weevil prefers to feed on strawberry and caneberry buds, it also damages other plants in the Rosaceae family, including geum (avens), potentilla, rose, cotoneaster, etc.

Figure 1 An adult strawberry blossom weevil, which was recently found in North America.

Adult strawberry blossom weevils are dark brown to black snout beetles and about 1/8th inch-long (Figure 1). Adults become active when temperatures reach 65 °F. Newly emerged adults first feed on foliage, leaving small holes in leaves. However, they soon migrate to floral tissues where females chew a hole before ovipositing a single, miniscule egg inside the bud. After the egg is laid, the female feeds on the pedicel of the bud, causing the bud to turn brown, where it either remains on the plant or drops to the ground.

Larvae emerge from eggs in about five or six days and feed on the floral tissues within buds. Within two weeks the tiny larvae become fully developed and pupate within the shriveled bud for about another two weeks before emerging as an adult. After feeding for a couple of weeks, adults then seek shelter in leaf litter or vegetation near soil surface where they diapause through the summer, fall, and winter months until they reemerge in the spring to feed on foliage and flower buds.

Figure 2 An adult strawberry bud weevil or strawberry clipper, which is commonly found in Missouri.

Anthonomus signatus, the strawberry bud weevil (also known as the strawberry clipper), is another snout beetle that damages strawberry, raspberry, blackberry, and other plants (Figure 2). Unlike A. rubi, this bud weevil is native to North America and is a common strawberry pest. Feeding injury includes "clipped" flower buds left dangling on the truss and small holes in flower petals. Yield losses from the strawberry clipper can be minimal in some years, but as high as 50 to 100 percent in some growing seasons. Early-season strawberry cultivars are usually more susceptible to injury than late-season cultivars.

Adult strawberry clippers are dark reddish-brown with a long snout and are slightly smaller than A. rubi. Adults emerge at about 60 °F, move to strawberry plants, where then puncture the flower buds with their snouts to feed on immature pollen. Thereafter, their life cycle is similar to the strawberry blossom weevil with one generation per year.

Cultural practices can be used to discourage strawberry clippers from remaining in the planting during their period of diapause. Immediately after harvest, mowing foliage during renovation, reducing plant debris, or plowing under old strawberry beds can help limit reduce these insects in future years. Alternatively, plants may be sprayed when three or more clippers are found in primary buds per three feet of row. Insecticide recommendations can be found in the Midwest Fruit Pest Management Guide.