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Insects (Maine Cranberries) - Cranberry Weevil

Order: Coleoptera || Family: Curculionidae (weevils or snout beetles) || Subfamily: Anthonominae
Scientific Name: Anthonomus musculus (Say)


Close view of a cranberry weevil, laying on its side, right next to a small portion of a US penny (for scale purposes) Photo of a Cranberry Weevil on the edge (frame) of a sweepnet (photographed July 20th in central Maine) Another photo of a Cranberry Weevil on the edge (frame) of a sweepnet (photographed July 20th in central Maine) Pair of mating Cranberry Weevils perched on the outer frame of a sweepnet (photographed July 20th in central Maine) picture of a Cranberry Weevil in the folds of a sweepnet (photographed June 17th) picture of a Cranberry Weevil resting near the handle of a sweepnet (photographed June 17th) fairly close picture of a cranberry weevil against a backdrop of the terminal leaves of a cranberry upright photo showing several Cranberry Weevils (crawling on the rim of a baby food jar) (photographed in early July) Picture of a Cranberry Weevil (closeup) on a cranberry blossom (photographed July 6th) photo showing obvious Cranberry Weevil damage to an unopened cranberry blossom (there are feeding holes and oviposition scars on it) Another photo showing heavy damage to a cranberry flower caused by Cranberry Weevil photos--with labels--showing a cranberry flower on the left, with an oviposition scar from a female weevil, plus a bulge in the flower pod where the developing weevil larva was, and then two photos on the right-hand side showing the actual weevil larva that was subsequently dissected out from the flower pod. photo showing cranberry leaf damage (on two cranberry leaves) caused by Cranberry Weevil feeding Photo of a pair of wild blueberry leaves showing numerous small holes as a result of cranberry weevil feeding injury


Background: Photo of a Cranberry Weevil, very close-up, resting on its side; reddish color is very apparentThis tiny beetle is native to North America, and so has a wide host range. Besides cranberry, as its name naturally suggests, it is also found commonly on black huckleberry, wild and cultivated blueberry, swamp sweetbells, staggerbush, dangleberry, sheep laurel, swamp honeysuckle, and on the flowers of chokeberry. It is also called the “blueberry blossom weevil.” As pointed out in Cranberry Insects of the Northeast by A.L. Averill & M.M. Sylvia (1998), more research needs to be done to find out whether other host or transitional plants surrounding a cranberry bed add to weevil populations by creating a reservoir of weevils, or if they act as trap crops, possibly drawing weevils away from cranberries.

More than 100 species of Anthonomus occur in North America. A few others of economic importance are the boll weevil (in cotton), the strawberry weevil and the apple curculio.


Pest Status: All snout beetles (except a few occurring in ant nests) are plant feeders, and many are serious pests, such as the one desribed here! Most snout beetles, including the cranberry weevil, will–when disturbed–draw in their legs and antennae, fall to the ground, and ‘play dead’ for several minutes, making them very difficult to find. In cranberry, adults are monitored by sweeping (25 sweeps per acre) with a 12″-diameter sweep net. The Action Threshold has historically been an average of 4.5 weevils per 25 sweeps.  In Maine, most sites have not experienced any detected presence of this pest, but it shows up from time to time at a few locations, and sometimes in extremely high levels, especially in organic settings.


Life Cycle:

Adults (2 separate broods): The overwintering cranberry weevil adult (which overwinters in surrounding woods) is about 1/10″ to 1/16″ long, dark red/crimson or a dark red-brown. Like all weevils, it has a snout (or beak), with its antennae arising from about the middle of the snout (see photos). They seldom fly because their bodies are heavy and stout, but when they do, they have been observed to make single flights of up to 75 feet. The weevils that are alive in the spring are referred to as the ‘Spring generation’ in order to distinguish them from the offspring of this generation, which are subsequently hatched out from the eggs that are laid later on, during bloom (these ‘brand new’ adults are thus referred to as the ‘Summer generation’).  Spring-generation adults are older and weaker, having had to overwinter, and so they are the ones that are targeted in spray programs (sprays on summer-generation weevils have not, to date, been effective). Sweepnet First Dates (in Maine) (Spring Generation adults): 6/8/01,  6/13/02, 6/20/07 and 6/2/09 (0 found in Year 2000)

Eggs: Females will insert a single egg between the petals of a developing blossom bud during June and July in Maine and Massachusetts. Many of the infested blossom buds (or pods) fall to the ground, some even before the egg hatches. In the lab at the UMass Cranberry Experiment Station, egg laying was observed in large, fully developed blossom buds. Females will often completely sever the pedicel with their mouthparts after laying their egg inside. But on smaller blossom pods, females tend to only partially cut the pedicel following egg-laying, creating a point of weakness. [The female weevil does this in blueberry as well]. Each female may lay 50 or more eggs in her lifetime, which can last at least 13 months. The smooth, round eggs are no larger than 1/16″ and are pale yellow in color.

Larvae: The white, legless grub is approximately 1/9″ long (one is pictured in the 3rd-to-last photo at the top of the page). As it grows, it will consume all of the internal flower parts. The larva then pupates, until it finally emerges as an adult. The entire life cycle–from egg to adult–takes about 2 months and can also be completed on wild and cultivated blueberry.


Control: The cranberry weevil is difficult to control. Late water and Fall floods are not effective against it. Sanding provides no benefit, either. Several materials are registered to use against it for non-organic, commercial growers, but in many cranberry parts of the country, cranberry weevil has developed a resistance to some of the broad-spectrum insecticides. For organic growers, one option that has been tried is a quick, 24-hour flood during the last part of June or 1st part of July. The flood may not kill many of the weevils, but it at least floats them off the cranberry bed and provides some temporary relief. Within a week’s time, at least half of the weevils have been observed to find their way back again, though. Still, it may make sense to try this under desperate circumstances. It is a risky maneuver, as a longer flood may result in the loss of the current year’s crop.

For specific and current control recommendations for Cranberry Weevil (for Maine), please refer to the Maine Cranberry Pest Management Guide.


Cranberry questions? Contact Charles Armstrong, Cranberry Professional. University of Maine Cooperative Extension || Pest Management Unit || 17 Godfrey Drive || Orono, ME 04473-3692 || Tel: 207.581.2967 [email: charles.armstrong@maine.edu]

 


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