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

Latin Name: Curculio Sayi

Appearance: American chestnut, like almost all tree species, has a number of host-specific insects that feed on it and little else. A number of moth species and at least two weevil species, the larger and smaller chestnut weevils, Curculio Caryatrypes and Curculio Sayi, are among these insects. Curculio Sayi, sometimes known as the little chestnut weevil, is a species of true weevil in the Curculionidae beetle family. The body’s typical length is around 1/4″ (6mm). Adults’ appearance might change from late June through July, depending on location and season – increasing degree days. Eggs are deposited individually, however many can be found in a single nut. When the larvae hatch, they feed on the tissue of the developing kernels.

Hosts Plants: American Chestnut, Chinese Chestnut, European Chestnut, and Chinquapin

Territory: North America

Damage Insect Cause: Weevil infestations can be controlled by picking up chestnuts every day and heating them to 140 degrees Fahrenheit for 30 minutes after curing to kill the larvae in the nuts. A cold treatment of keeping the nuts at 0 F for four days may also be useful, however it may impair the taste of the nuts.

Life History and Habits: Adults of the lesser chestnut weevil emerge from the soil in Michigan at two distinct times: first in the spring around bloom (May-June) and again in late summer-early fall shortly before burrs erupt (September-October). Weevils may be seen munching on catkins when they develop in the spring. When the number of catkins decreases, the population vanishes. It’s unclear if these spring weevils will return to the soil or go on to feast on other plants. A second wave of smaller chestnut weevils emerges in September and October. The bulk of egg laying happens as burrs begin to open for both spring and fall emerging adult weevils.

Eggs are normally laid in the downy lining around the nut and hatch in about 10 days, after which the larvae feed on the kernel and grow within the shell. Larvae gnaw an exit hole in the nutshell and fall to the earth after two to three weeks. The majority of weevils overwinter as larvae the first year, pupate in the soil the next fall, then overwinter as adults the following year. The entire lifespan takes two to three years to finish.