The Biology of a Little Known Weevil: Polydrusus Impressifrons
BIOLOGY OF A LITTLE KNOWN WEEVIL:
Jack C. Niedbala
Washington State University, Department of Entomology, Pullman, WA
The pale green weevil (PGW, Polydrusus impressifrons Gyllenhal [Coleoptera: Curculionidae]) is native to Europe where it belongs to a group known to contain destructive species. However, in Europe PGW is considered to be of little economic importance. The weevil was first reported in the United States in the summer of 1906 in Geneva, New York, and then later in Ontario County, New York. Since then, the weevil has dispersed across North America where it has become a pest of residential trees and crops like poplar. Adult weevils are approximately 0.7 cm in length and covered with iridescent greenish or sometimes yellowish scales. The pale green weevil is an omnivorous defoliator with a wide host range: poplar, birch, willow, apple, and pear are some of its favorite host plants.
Partial life history of the weevil is known. Adults emerge from the ground at the base of host trees starting in May. They immediately begin to mate and lay eggs. Eggs are laid in crevices, holes in the bark, or in wounds on the tree surface. Eggs are laid singly or in groups of up to eighty-five. Newly eclosed larvae are approximately 0.07 cm in length. Larvae drop to the ground and move into the soil to feed on the roots of the host plant. Mature larvae over-winter and pupation occurs in the later part of April.
The larval stage of the weevil is largely unknown and possibly an appropriate stage for controlling the pest due to the fragile nature of larva.