Common Name: Alfalfa weevil
Scientific Name: Varies
Description: Adult beetle is a brown weevil, about 0.12 to 0.2 inches long, with a downward projecting beak and a wide darker stripe down the middle of the back. The color may vary from almost uniform brown to nearly black. Larvae are legless, plump-bodied and yellowish when young turning to pale green as they get larger with a white stripe down the center of the back and thinner white stripes closer to the sides. The head is a dark brown to black. Larvae are up to 0.4 inches long.
This is the most common weevil on alfalfa. A few other species may show up on alfalfa but they are less likely to be of economic importance. An introduced ichneumon wasp, Bathyplectes curculionis, parasitizes the larvae and has helped with controlling this pest.
Life Cycle: The eastern form spends the winter as eggs and the western form spend the winter as adults. Females lay eggs in cavities in the stems of alfalfa. Yellowish eggs are laid in clusters on the plant. Larvae develop in the spring through three or four stages (instars) over 29 to 58 days. They pupate in cocoons in the soil and adult weevils emerge in about 10 days. There is one generation per year with adults living 10 to 14 months. Adults readily fly and migrate to new fields.
Habitat and Food Source(s): Chewing mouthparts for adults and larvae. Alfalfa is the primary host plant, but they can also be found feeding on bur clover, sweet yellow clover, vetch and sometimes on other clovers. Both adults and larvae feed on foliage or buds. Feeding causes leaves to appear shredded (skeletonized). High population densities can completely defoliate spots in the field, resulting in sections appearing whitish. Injured plants are stunted when the bud is removed by feeding.
Pest Status: The most important pest of alfalfa nearly anywhere in the United States; can reduce the alfalfa stand, often causing the loss of one cutting of alfalfa; introduced from southern Europe sometime around 1900 and was first observed in 1904 near Salt Lake City, Utah; medically harmless.
Literature: Metcalf et al. 1962; Swan & Papp 1972.