The plum curculio, Conotrachelus nenuphar (Herbst), is an important early season pest of pome and stone fruits. They can cause considerable damage to apple, pear, apricot, peach, plum, nectarine, cherry, and other fruits. After codling moth, plum curculio is often regarded as the most serious pest of tree fruits in eastern North America.
Biology and Life History
Plum curculio adults are a type of weevil (or snout beetle), approximately 6 mm (¼”) in length with a mottled combination of brown, black, and gray colors over the body (Figure 1). They have four small humps on their wing covers (elytra) and a characteristic curved snout.
The adults overwinter in ground debris within woodlands or along field edges and begin moving into tree fruit plantings in the spring to feed on buds, flowers, and newly formed fruit. Egg laying begins as soon as fruit set occurs. Surface feeding and egg-laying by weevils can scar or deform fruit by harvest (Figure 2). The crescent-shaped scars cut into the fruit surface from egg-laying are a characteristic sign of plum curculio damage.
Figure 1. Adult plum curculio,
Figure 2. Plum curculio damage. Superficial egg-laying (D-shaped marks) and feeding (small spots) scars on a mature apple fruit (black and white image). Photo courtesy of New York State Agricultural Experiment Station Archive, Cornell University. Bugwood.org.
In apple, plum curculio larvae are unable to complete development within growing fruit because of the pressure exerted by the hard, expanding tissue. However, feeding by larvae can cause fruit to drop prematurely from trees and it is within these apples that they are able to complete development. Larvae will generally spend two to three weeks feeding within fruit before exiting to pupate in the soil. The next generation adults emerge in late summer and also feed on fruit, but they generally do not reproduce until the following spring.
There are few effective non-chemical methods for controlling plum curculio in tree fruits. However, home orchardists can help reduce future populations by promptly picking up and destroying any fallen fruit from the ground. Adult populations can be suppressed in the spring with well-timed applications of effective insecticides. Please consult your local production manual for recommendations suitable to your area.