Cranberry Weevil
Order: Coleoptera || Family: Curculionidae (weevils or snout beetles)
|| Subfamily: Anthonominae
Anthonomus musculus (Say)
Photos by C. Armstrong
This tiny beetle is native to North America,
and so has a wide host range. It is found commonly on: black huckleberry,
wild and cultivated blueberry, cranberry--as the name indicates--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
Averill & Sylvia, 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, drawing weevils away from cranberries.
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.
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.
ADULTS: 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, but when they
do, they have been observed to make single flights of up to 75 feet.
Photo 1 (June 8th,
2001)
Photo 2 (June 8th, 2001)
Photo 3 (July, 2001 - A
pair of cranberry weevils crawling along the top of a baby food jar)
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 would then completely sever
the pedicel with their mouthparts. But on smaller blossom pods, females
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 (see photo). 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.
A developing cranberry
weevil larva (grub) as seen through a dissecting microscope;
Note the brown frass on its body. [Dissected
from a cranberry blossom on June 23rd, 2001]
Management: The
cranberry weevil is difficult to control. Late water floods, Fall floods
and sanding are not effective against it. Several materials are registered
to use against it for non-organic, commercial growers (check the Maine
Cranberry IPM Guide), but in many cranberry parts of the country, cranberry
weevil has developed a resistance to some of the broad-spectrum insecticides.
For organic growers, the only current tactic
that has been attempted 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 find their way
back again, however. 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.
If you have comments or questions about this page,
contact Charles Armstrong at: charlesa@umext.maine.edu
Putting
knowledge to work with the people of Maine
