Large Chestnut Weevil: Appearance, Territory, Damage and Life Cycle

Latin Name: Curculio Caryopteris

Appearance: The lesser chestnut weevil is the most common insect pest of chestnut trees in the central and eastern United States. The large chestnut weevil is also a significant pest, but it is less common. These pests have not yet been a serious concern for Michigan producers, but as the state’s acreage grows, growers must carefully screen for chestnut weevil. The bodies of larger chestnut weevils are sturdy and dark brown or tan with brown mottling or stripes. The large and smaller chestnut weevils are native weevils that only infest tree species in the genus Castanea. The eggs of the smaller and larger chestnut weevils are laid on maturing nuts. The larvae eat within the nut, causing the kernel to deteriorate. These weevils may infest and kill the bulk of the nuts produced in an orchard if left unchecked.

Hosts Plants: The large and smaller chestnut weevils are widespread to North America and are host-specific, infesting only Castanea tree species such as American chestnut, Chinese chestnut, European chestnut, and chinquapin.

Territory: Africa, Asia, Europe, and North America

Damage Insect Cause: This season, chestnut producers must be on the lookout for this potentially destructive insect. Both the large and lesser chestnut weevil lay eggs on growing nuts, and the larvae feed on and compromise the kernel. If the larvae are not controlled, they can infest and kill the nuts. To suppress chestnut weevils, chemical, cultural, and post-harvest treatments are available. In an ideal world, a combination of cultural and chemical management would control the pest while eliminating the need for post-harvest treatment, which can reduce quality and marketable output. Sanitation is a critical component in pest management. Collecting and removing dropped nuts will keep larvae from growing in the orchard.

Life History and Habits: Under Michigan circumstances, large chestnut weevil adults will most likely emerge in August or September and begin laying eggs in juvenile burrs nearly soon after emergence. The larvae eat and develop within the nut for two to three weeks before chewing a small exit hole and exiting the nut. The larvae of the huge chestnut weevil normally depart the chestnut before the nuts fall to the ground and overwinter in the soil. Pupation and adult emergence occur the following summer, with a small population of larvae overwintering for a second winter prior to pupation. The entire lifetime takes one to two years.