The codling moth, Cydia pomonella, is a constant threat to apple production in Pennsylvania. This species, along with another internal fruit feeder, oriental fruit moth, Grapholita molesta, and lesser appleworm, G. prunivora, has been known to infest the majority of fruit in untreated orchards. Despite similarities in the way the larvae damage fruit, each species require a special set of treatments at different times during the season. Proper identification of the problem is a crucial to effectively control the pest.
The adult codling moth is approximately 3/8 inch long and grayish in color. The wing is generally a darker shade of gray near the base, with a dark patch containing coppery scales near the inside wing tip. The larvae have a cream to pinkish body and a brown head with dark speckles on the prothoracic shield (the collar behind the head). When fully grown, larvae are from 1/2 to 5/8 inch long. Larvae of the other two species are smaller but otherwise closely resemble the codling moth. The eggs, laid singly, appear as flat, slightly ovoid, discs.
The codling moth overwinters as a full-grown larva within a cocoon under leaf litter, loose bark scales, or any other sheltered place it might encounter. Pupation occurs at about first pink bud, with first flight occurring about the first week of May (full bloom), and peak flight occurring approximately 2 weeks after full bloom. First-generation eggs are laid on leaves near the fruit or on the fruit itself and develop in about 8 to 14 days (first cover spray, about 2 weeks after petal fall on apples). The newly hatched larvae bore through the fruit surface, generally at the blossom or calyx end, and feed near the surface for a time before boring to the core. Here the larvae feed on the seeds and surrounding flesh until they are fully grown in 3 to 4 weeks. Then, they exit the fruit, seek shelter, spin a cocoon, and may or may not pupate. Some first-generation larvae that do pupate emerge as adults in 2 to 3 weeks (fourth or fifth cover spray, July 15 to August 1) and produce a second generation. The majority of the second generation overwinters as mature larvae.
First-generation larvae that do not pupate enter a quiet phase, overwinter as larvae, and pupate and emerge as adults in the spring. Individuals of the second generation may also pupate and attempt to produce a third generation (seventh or eighth cover spray, September 1 to 15). This generation, which does not survive the winter, is termed a suicide generation. Individuals can, however, inflict additional late-season fruit injury.
Codling moth damage to apples can appear as tunnels or "stings." Tunnels originate in the calyx or, particularly in the later generations, from the side of the apple and extend to the core. Codling moth larvae that feed on the core characteristically leave frass (excrement) exuding from the point of entry. Stings result from limited feeding and are often small, shallow holes the size of pinpricks with a little dead tissue on the cavity walls. They are caused by early instar larvae that have been poisoned and die shortly after puncturing the apple skin. Oriental fruit moth larvae are less likely to feed on the seeds than are the larvae of codling moth; lesser apple worm larvae feeding is limited to just beneath the skin, either on the side of the fruit or in the calyx.
Controlling the codling moth requires careful monitoring and timing of insecticidal applications, which must coincide with the hatching of larvae. If insecticides are applied too late, the larvae will have had time to tunnel into the fruit and will be sheltered from the effects of any treatments. Applications should begin at late petal fall. To protect pollinators, spraying should not be done during full bloom. Following the petal fall application, cover sprays are necessary to protect the fruit from recently hatched larvae. Controls might be necessary with the hatching of the second and possibly the third generations, depending on conditions in the orchard. Fruit should be examined in mid- to late June for evidence of frass and to determine the need for control of the second generation. Some level of codling moth reduction can be achieved by maintaining good orchard sanitation and removing loose bark from old trees. It might help to place corrugated cardboard bands around apple trunks in September to trap larvae, which should be removed and destroyed in December. If pesticide applications are necessary, the broad-spectrum insecticides (e.g., carbaryl, compounds from the pyrethroid group, rotenone) are recommended. The attract-and-kill material Last Call CM mating disruption can also be successfully used to control this pest as well. In orchards where excellent spray coverage can be achieved, the natural product codling moth granulosis virus can be applied to reduce the codling moth population.