Family – Pyralidae

Egg: The eggs are ovoid with a strongly reticulated surface of triangular facets. They average 0.35 mm wide by 0.60 mm long. Immediately after oviposition the eggs are white, but they change to a tin hue to pink and eventually to a deep pin-red as they develop. They are laid singly or in small, loose clusters.

Larva: The color of the larvae varies from dusky white to grayish purple with the dorsum darker than the underside, though many specimens taken are dark lavender or dark red. The head capsule, cervical shield and anal plate vary from dark yellow to dark brown and often exhibit indefinite pigmented areas. Only long and distinct primary setae are present, giving the larva a bristly appearance. The larva is 18 to 25 mm long; its head capsule is 1.7 mm wide.

Hibernation: The larvae overwinter in silken cocoons that appear identical to those in which they pupate. All instars are capable of forming them for overwintering purposes. The hibernacula are most often located amidst frass accumulations, though the frass particles are not a structural component of the hibernaculum, as with the lesser peachtree borer.

Pupa: Pupae are enclosed in chitinous cases within silken cocoons beneath the bark near previous feeding sites. Female pupae average 12 mm in length; males, 11mm. Immediately after pupation the pupae are translucent white, but they quickly change to brown and eventually near-black prior to adult emergence, which occurs in about 2 to 2 ½ weeks. When the adult emerges, the remaining pupal skin is usually retained within the cocoon, though occasionally it may protrude slightly.

Adult: The adult males and females are dull grayish purple with an irregular transverse band two-thirds the distance to the outer forewing. The hind wing is entirely grayish tan, and both wings have a short fringe on the outer margin. The average wingspan is between 20 and 25 mm. The female is slightly larger than the male.

The American plum borer has been located in a wide variety of forest, ornamental and fruit trees across southern Canada and the United States. Infestations of this insect have been reported in commercial plantings of sweet and tart cherry, apple, apricot, peach, pear, plum and nectarine.

American plum borer larvae feed on the cambium of the tree. On apple it has been reported feeding on burr knot tissues in association with the dogwood borer. Infestation of healthy, non-wounded tissue is rare. In cherries, 90 percent of all larvae will be found in the 2- or 3- foot trunk area between the ground and the bases of the scaffold branches. They are not commonly found on the branches. They are not commonly found on the branches above the main trunk.

The larvae tend to be somewhat gregarious – for as many as 20 larvae to occur around a single wound site on a tree is not uncommon. As a result of larval feeding, wounds often do not heal properly, and tree vigor is continually diminished as more cambial tissue is consumed. The extent of larval feeding is seldom apparent because the bark directly above the immediate feeding area appears normal, even when the larvae have advanced several inches from the wounded area. With enough time, they will completely girdle the tree. A 4- to 6- inch scaffold limb can be rendered commercially unproductive in two years. Open wounds, sap flows and frass accumulations also act as excellent nutrient reservoirs for fungi and other insects that further damage tissue.

Second-generation larvae feeding on black knot of plum have been observed leaving the black knot to feed on ripening fruit.

The advent of mechanical harvesting of cherries has been responsible for this insect changing from a minor to a major pest of cherries. The highest infestations occur in older orchards that have experienced several years of wounding, especially where mechanical harvesting is used. The larvae thrive on cambium tissue, and any wounds that expose cambium are prone to infestation. Open wounds and sap flows are very attractive to the females as oviposition sites.

Black knot on plums is extremely attractive to the American plum borer. Large populations often develop on these sites.

The insect overwinters beneath the bark as a larva within a hibernaculum formed during mid- to late October. It resumes feeding in early spring as temperatures rise. The overwintering larvae begin pupating in early to mid-April, and first-brood adults emerge in early May. These first-brood adults continue to emerge into early June, with peak emergence in mid-May at the white-bud stage. The adults generally emerge about mid afternoon. They live for a minimum of two weeks. They are nocturnal in habit and, because of their cryptic coloration, are seldom seen in the field. In the resting position, they assume a twig-like posture by resting motionless, with the head and thorax held away from the twig and the abdomen pressed tightly against the bark. They fly over short distances with an erratic flutter. Egg laying occurs throughout this period, with eggs deposited singly or in small clusters in cracks near the cambium, especially in and around wounds. Each female deposits an average of 25 to 50 eggs over a period of two to three days. The eggs are laid at night. The larvae emerge in about nine days. Development time from first-instar larvae to pupae is about five weeks.

The larvae feed beneath the bark, favoring areas with available cambium and frass accumulations for protection. For this generation, pupation occurs from mid- to late June. The second-generation adults emerge from early July to mid- September, peaking in mid-July. This second emergence and egg-laying period coincides with most mechanical harvesting schedules for cherries, thus creating an ideal situation for oviposition because wounds are readily available. The following generation of larvae continues feeding until temperatures fall and trees harden off in about mid-October, at which time larvae seek form hibernacula.

Examine the trunk area up to 3 feet from the ground level for frass and fresh gumming with frass. Place pheromone traps in trees at the end of April. Replace caps and traps near the end of June for the summer generation. Use three traps per block. An average of more than six adults per trap per week indicates a potential problem. Be aware that alternate host plants, especially near wooded areas, can interfere with trap catches.

Apply an effective pesticide with a hydraulic gun directed at the trunk at the white-bud or petal-fall stage on tart or sweet cherries, when the first generation adults are emerging. Some pesticides will provide seasonal control of first and second generations with a single application at the white-bud or petal-fall stage.

This table shows the relationship between the flights of American plum borer, peachtree borer and lesser peachtree borer.