Fruit IPM Fact Sheet Fruit IPM Fact Sheet PLUM CURCULIO
From NCR-63:Common Tree Fruit Pests, by Angus H. Howitt, Michigan State University
The Plum Curculio is one of the most important
insects attacking tree fruits. It is particularly destructive, and the problem is
intensified where stone fruits and apples are interplanted.
Overwintering adult beetles
attack the fruit soon after it forms and eat holes through the skin and feed on the pulp,
usually next to the pit. The female makes distinctive, crescent-shaped wounds on the skin
when laying eggs.
Plum curculio is capable of causing great damage and is considered a difficult pest to
control. Unfortunately, there are no pheromones for this insect and no reliable monitoring
methods other than jarring branches over a beating tray or light-colored ground cover for
collection and identification. If using this monitoring method, do so during the
petal-fall or shuck-split stage or during the first-cover period, especially after a few
days of warm weather. Select trees near wintering hibernation areas such as woodlots,
fences or ditches.
Apply sprays at the petal-fall and shuck-split stages. Be aware that if weather is
unfavorable during bloom and shuck-split, adults may not leave hibernation quarters until
after shuck-split is over. Under such conditions, you may need a first-cover application
and possibly a second-cover spray.
Life Stages:
Egg: T
he egg is 0.4 mm
wide, 0.6 mm long, pearly white and elliptical. The female first constructs a cavity under
the skin of the fruit to receive the egg. Then, turning around, she deposits the egg near
the mouth of the cavity, forcing the egg into the cavity with her ovipositor or beak. She
then cuts a crescent-shaped, oblique slit underneath the egg cavity to leave the egg in a
flap of flesh. Crescent-shaped scars present on apple fruit at harvest result from eggs
that did not hatch or that were killed by pressures exerted by the growing fruit.
Larva: The larva is whitish and legless. When
full grown, it measures about 6 to 9 mm long. The larva is slightly curved or bow-shaped
and tapers slightly at each end. It has a brown head and a light brown shield behind the
head. There are four larval instars.
Pupa: The pupa, which is found in the upper 1 to 2 inches of soil, is whitish or cream-colored and measures 5 to 7 mm. All of the adult structures, such as eyes, mouthparts, etc., are visible just before transformation into the adult.
Adult: The adult is a small, rough snout beetle, 4 to 6 mm long and mottled with black, gray and brown. Four pairs of ridges occur on the wing covers, but because the middle humps on each wing cover are larger, it appears to have only two humps. The sharp, biting jaws are located on the tip of a long curved snout.
Host Range
The hosts of the plum curculio are apple, nectarine, plum, cherry, peach, apricot, pear and quince. The plum curculio can survive on wild plum, hawthorn and native crabapple. The plum curculio is generally distributed over the eastern states and in Canada, east of the Rocky Mountains.
Injury or Damage
Injury caused by the plum curculio can be grouped into four principle classes:
and egg laying by
the overwintering beetles early in the spring appear as crescent-shaped scars (oviposition
injury) on the fruit, or as bumps (feeding injury) that protrude from the fruit at
harvest. Badly attacked fruit my be knobby, gnarled and scarred at harvest. 
Factors Affecting
Abundance
Moisture and temperature regulate plum curculio activity. Moisture is necessary early in the spring to restore normal water relationships within the beetles. The exact role of water in the biology is not known, but it has been observed that beetles need water before much activity takes place. Also, beetles are more active on warm, damp, cloudy days and in thick, heavy trees that provide abundant dampness in the centers.
Temperature is the most important factor in plum curculio activity, particularly early in the spring. Several formulas have evolved to predict when beetles leave hibernation quarters and move to the trees to lay eggs or feed. They are:
All formulas work out about the same under field conditions. High winds, which cause considerable movement of the trees, will shake the beetles from the trees. High winds and low humidity cause beetles to leave the trees and burrow into the soil in search of moisture.
The beetles' activities are about equally distributed between day and night.
Life History
When temperature and moisture conditions are favorable in the spring, the adult beetles leave their hibernation quarters in trash on the ground, woodlots or hedgerows, and migrate to the trees. This usually occurs just about the time of bloom.
Migration continues for up to six weeks after bloom, with the largest migration occurring within the period up to 14 days after petal fall. The adults do not like strong light and prefer the dense shade of the tree's inner canopy.
After mating, the female deposits eggs into the fruit. Each female is capable of laying from 100 to 500 eggs. The incubation period for the eggs is about one week. The young larvae bore to the center of the fruit, where they feed until reaching maturity. Many infested fruits drop to the ground in June. After about 16 days in the larval stage, the full-grown larvae leave the fruit, enter the soil to a depth of about 1 inch, construct pupal cells and pupate. The length of time between larval entrance into the soil and the emergence of the new adult is about 30 days. The complete cycle from egg to adult takes about 50 to 55 days. After the adults emerge from the soil in late summer, they will feed on maturing apples until cold weather forces them into hibernation quarters.
Monitoring
During petal fall and the first cover period, tap the foliage or small limbs in early morning and catch the adults on a beating tray. Check the developing fruit for feeding and oviposition injury, especially after rain. The activity of this pest is closely related to temperature-75 degrees F is highly favorable, and activity decreases at lower temperatures. Below 60 degrees F, activity is negligible. If temperatures reach 70 to 75 degrees F for two days before the petals fall, the beetles have opportunity to feed and mate.
Control
Petal-fall sprays and the first and second cover sprays are directed at the adult and the egg-laying period. Once the fruit is exposed, the females can lay many eggs in a short time cause considerable damage. Under these conditions, a prompt petal-fall spray should be applied. If the weather is cool at bloom time and petal fall, the beetles may not leave hibernation quarters and move into the fruit trees until first cover. Under these conditions, a first cover application and possibly another application at second cover will be needed. Applications made at petal fall will not be fully effective under these conditions. Plum curculio is considered a difficult pest to control and requires a full dosage of an effective pesticide.
The Plum Curculio is a major pest of stone fruits, affecting (in ranking order) nectarine, plum, cherry, peach and apricot. Overwintering adult beetles attack the fruit soon after it forms and eat holes through the skin and feed on the pulp, usually next to the pit.
The female makes distinctive, crescent-shaped wounds on the skin when laying eggs. In many cases, the beetles introduce spores of brown rot fungus to fruit during feeding. Infested fruits usually fall prematurely, though cherries remain on the tree until ripe. In early peach varieties, the fruit matures about the same time as the curculio larvae, and larvae may be found in these peaches at harvest.
To distinguish between 
larvae of plum curculio and Oriental fruit moth , examine the leg area. Plum curculio
larvae have no legs; Oriental fruit moth larvae have three pairs of true legs and five
pairs of prolegs on the abdominal segments.
To distinguish between cherry
fruit fly larvae and plum curculio larvae, examine the head capsule. Plum curculio
larvae have distinct, hard brown head capsules with well developed opposable mandibles.
Cherry fruit fly larvae (maggots) do not have head capsules and have curved mouth hooks
rather than mandibles (jawbones). Furthermore, cherries infested with maggots will sink in
water cooling tanks at harvest; cherries infested with curculio larvae will float because
of large air spaces left around the pit during feeding. Cherries infested by plum curculio
may be floated off the rest of the cherries and disposed of.
