PECAN NUT CASEBEARER
The pecan nut casebearer, Acrobasis caryae Grote, is the major pest of pecans in Texas. Early in the spring, the overwintered generation feeds first in the buds and then in the developing shoots, causing them to wilt and die. Succeeding generations feed on the nuts during the late spring and summer, [Figure 9]. Severe infestations may destroy the entire crop of pecans.
The adult is a light gray moth which is about one third inch in length. The wings are gray, and the forewings have a ridge of dark scales across them about one-third the distance from the base. The moths fly at night and spend the day in concealment.
The young larvae are white to pink, but later become olive gray to green and attain a length of about one-half inch.
This insect passes the winter as a partially grown larva in a tiny silken cocoon called a hibernaculum, which is usually attached to a bud, [Figure 10]. In the spring, the larvae feed for a short time on the buds, after which they tunnel in the developing shoots until they reach maturity, [Figure 11]. Pupation usually occurs in these burrows, and the moths emerge in late April and May.
Two or 3 days after the adults emerge, they deposit eggs on the tips of the nuts, [Figure 12]. Each female may deposit from 50 to 150 eggs. The eggs, which are just visible to the naked eye, are greenish white when they are deposited but assume a reddish appearance a few days later. The first-generation larvae hatch from the eggs in 4 or 5 days and migrate to the buds below the nuts to feed. After a day or two, they enter the nuts, usually at the base, and feed in them, each larva frequently destroying an entire cluster. Bits of frass and webbing may be observed projecting from the injured nuts. Upon reaching maturity, the larvae pupate in the nuts and emerge as adults in June and early July.
Figure 9. Injury to nuts caused by first generation larvae of the pecan nut casebearer.
The adults deposit eggs in grooves on the tips or bases of the nuts. Second-generation larvae which hatch from these eggs also feed in the nuts. Less injury is produced by this generation because the nuts are larger and each larva requires only one or two nuts to complete its development. Pupation takes place in the hollowed out nuts, [Figure 13], and the moths emerge from late July to early September.
A third generation usually follows, but the shells of the nuts have become hard, and only a few of them are penetrated by the larvae. Instead, they feed in the shucks. A number of third-generation larvae construct hibernacula, while the remainder pupate and appear as adults, emerging from late August to October. These adults deposit eggs, which hatch into fourth-generation larvae. If nuts are available, their shucks constitute the principal food of the larvae of this generation. In the absence of nuts, the larvae feed on buds and leaf stems. Overwintering hibernacula are constructed by the partially grown larvae by the middle of November[2].
Control.—The necessity for control of this pest may be determined by examination of the trees when the shoots appear in the spring. If a number of them are wilted, the following control measures probably will be required.
A spray application should be made when eggs of the first generation appear on the tips of the young nuts in late April or May. The period of egg deposition usually coincides with the completion of pollination, at which time the tips of the nuts turn brown. Satisfactory control may be obtained by using any of several insecticides. See spray schedule, [page 4].
Ordinarily, only one application of spray is required to control the nut casebearer. However, if trees surrounding the treated area are not sprayed, moths may enter the sprayed area and a serious infestation of second-generation larvae may develop. Under these circumstances, a second spray may be required in June or early July when second-generation eggs are deposited[6], [11].