The recent arrival (March 3, 2011) of a digital image of the black vine weevil (BVW) collected from a kitchen floor in Delaware County was a reminder of just how uncommon this insect pest in Iowa. The previous sample appears to have been diagnosed back in 2006.
Only a small handful of black vine weevils have been identified from only 9 Iowa counties in the ISU Plant and Insect Diagnostic Clinic. Almost all reports have come from homeowners who were bothered by the adult weevils appearing as accidental invaders inside the home between October and March.
Adult black vine weevils will feed on over 100 different kinds of plants but prefer yews (Taxus) and rhododendrons. Taxus capitata seems to be particularly susceptible to attack. Adult feeding causes small crescent shaped notches along the leaf margins. Iowa Department of Agriculture & Land Stewardship nursery inspectors report observing occasional BVW leaf feeding damage on containerized rhododendron, yew, and sometimes azalea coming from out-of-state, but there are no apparent indications of a large or ongoing problem in the state.
Black vine weevils are oblong oval in shape, about 1/2-inch long and have a short, broad snout with elbowed antennae. The body is slate gray to blackish brown and the wing covers have numerous small pits and patches of short yellow hairs. See the photo below.
Black vine weevil adults develop from white legless larvae that live in the soil under infested plants. The larvae feed on young, tender roots. Leaf feeding by the adults seems to have little effect on plant health. Heavy infestations of larvae may cause stunting or death of infested plants. Only females are known in North America, and one generation occurs outdoors annually. They are easily transported in potted plants or transplants using a soil root ball.
As mentioned, the black vine weevil has been troubling in Iowa as a harmless annoyance indoors after wandering in from infested plants in the landscape. The black vine weevil can not bite, sting or carry diseases. It does not feed on or damage the house structure, its contents or occupants. It is only a pest because of its presence. These weevils can not fly but they are very active walkers. They are most active at night.
Black vine weevils found indoors need only be swept or picked up and discarded. Spraying is unneccesary and generally ineffective. Susceptible plants in the landscape should be watched for signs of weevil feeding in early summer. Treatment of infested plants in Iowa has not been necessary to this date.
Black vine weevil adult. Photo by Cheri Hildebrand.