The plum curculio is widely distributed east of the Rocky Mountains and is native to North America. The plum curculio can be very destructive, attacking not only plums, but also apples, peaches, pears, cherries, quince and other wild and cultivated fruits. Injury results from the spring feeding of adult beetles, from female ovipositioning in the fruit, from the feeding of larvae within the fruit and finally from the early fall feeding of adult beetles.

Description:

The adult plum curculio is a small, hard-bodied, brownish-black snout beetle mottled with white and orange areas. It has four prominent black humps on its top surface. It is about 6 mm (1/4 inch) long and has a long snout, the end of which bears chewing mouthparts. The fully-grown larva is about 9 mm (3/8 inch) long and is a yellowish-white, legless grub with a brown head.

Life Cycle:

The plum curculio overwinters as an adult under yard debris or in protected parts of an orchard. In spring, shortly after peaches bloom or when apples are near the pink stage, the beetles come out of hibernation and begin to fly to fruit trees to feed. Egg-laying begins as soon as the young fruits form and continues for three or four weeks. To lay eggs, the female cuts a small, round cavity directly under the skin of the fruit with her mouthparts. She then lays a single tiny white egg in the cavity, just under the skin of the fruit. Next she cuts a crescent-shaped slit nearly halfway around the cavity, creating a dead flap in the surface of the fruit. A single female lays about 60 to 150 eggs. Within seven days, larvae emerge from the eggs and begin to eat their way through the flesh of the fruit. In stone fruits, the larva works its way toward the pit, around which it feeds extensively until it is fully grown. On apples, few if any of the young larvae survive if the apple continues to grow on the tree because the egg or larva is crushed by the growing tissues of the fruit. If the apple drops prematurely or is picked from the tree while the larva is still alive, or if the variety is early-ripening, the larva can complete its feeding and growth. The larva spends about 10 to 16 days feeding.

When fully developed, the larva burrows out of the fruit, making an oval exit hole, and enters the soil. In the soil, the larva constructs a small cell in which it transforms into a whitish pupa and then into an adult. The time between the entrance of the larva into the soil and the appearance of the new beetle above ground is about five weeks.

Summer brood adults emerge in July and August. They do not lay eggs but instead feed on fruit, showing a preference for smooth-skinned fruits such as apples and plums. On apples, the beetle makes a small hole in the skin of the fruit and then devours all the flesh of the fruit it can reach with its snout. This feeding takes place until the adults enter hibernation, which occurs from September through early November.

Damage:

Both the adult and larval stages injure fruits. In spring, adults feed on buds, blossoms, leaves and new fruits. Feeding scars appear as shallow cavities on the fruit surface. The major injury occurs from the laying of eggs by the curculios (weevils) as described above. The early feeding and egg-laying punctures can cause marked scarring and malformation of the fruit. Early feeding on the surface of peaches often causes severely deformed fruits known as "cat-faced" peaches. Larval feeding in apples can cause distortion of the fruit. The mechanical injury by adults in feeding and egg deposition can cause premature fruit drop. When the summer brood of adults appears, feeding cavities again can be found on the fruits.

Control:

Physical: Mechanical control--jarring the sluggish beetles from trees in the morning and capturing them on sheets--is practical on a small scale. Natural control of the curculio results from winter mortality, attacks by birds and other predators, and from parasites. Sanitation can also lessen damage. Pick up fallen fruit two to three times a week and put it in a plastic bag, tie the bag tightly and place it in the trash can. This will help keep larvae in fallen fruit from developing in the soil and, if done regularly, can minimize damage.

Chemical: On apples and pears, apply an all-purpose fruit tree spray or the insecticide phosmet (Imidan) when the petals fall from the blossoms and again 7-10 days later for the first generation beetles. Second generation beetles only feed on the fruit skin and their damage can be tolerated. For an overview of home apple tree management and sources of disease-resistant fruit trees, see "Home Tree and Small Fruit Pest Management Guide," or visit the URI Apple IPM website at http://www.uri.edu/research/IPM.

Adapted from the Ohio State University Extension, 1999