Life history and habits

The codling moth overwinters as a full-grown caterpillar within a cocoon, pupating in winter or early spring, typically within days of apple bloom. Mating occurs within a few days of adult emergence, followed by egg laying thereafter. Eggs are deposited singly on leaves; each egg is about the size of a pin head. The number of eggs laid per female ranges from 30 to 70. The eggs will hatch in six to 14 days, depending on temperature. Within 24 hours of hatching, the larvae bury into the fruit. As the caterpillars grow, they molt five times, going through five larval stages before they are full-grown. Once full grown, the larva emerges and seeks a protected site to spin a cocoon. Sites are typically beneath bark or underneath debris around the base of the tree. A second, and sometimes third, generation can be produced in a single summer.

Injury

Caterpillars tunnel through the flesh of apples, often attacking areas that provide some cover, such as the end, calyx, stem end, or where two fruit touch. Codling moths can also infect pears and are rarely found in cherries, peaches, and large-fruit crab apples. Although caterpillars’ tunnel through the fruit flesh, most of the feeding is on developing seeds in the core. When the caterpillars are fully grown, they tunnel out of the fruit, creating larger wounds and leaving behind piles of brown excrement. 

Monitoring

Several traps can be used in management of codling moth. Some are helpful in detecting when moths are active, which allows for more targeted use of pesticides. The spring emergence of codling moths can be easily monitored using the use of pheromone traps. Pheromone traps only attract males, but can be used for scouting.

Biological control

There are many natural controls of codling moth: some parasitic wasps and a host of generalist predators (e.g., assassin bugs, minute pirate bugs, green lacewing larvae). These predators provide important supplemental control on unsprayed trees or trees where insecticides are selective in their effects. Of the natural enemies, Trichogramma wasps have a great biological control potential. However, due to the serious nature of codling moth injury in which a single larvae can destroy a fruit, natural enemies often will not provide effective control.

Cultural control

There are no apple or pear varieties that are completely resistant to codling moth, although firmer fruits are somewhat less susceptible. It is recommended to remove infested fruit, debris from the vicinity of the tree base, and flaps of bark on older trees. Banding tree trunks with cardboard or burlap bands can provide sites where codling moth will pupate where they can then be collected and destroyed. Individual fruit can be enclosed in a small paper bag to exclude codling moth. Thinning fruit that are in contact is also recommended, which will improve spray coverage.

Chemical control

There are limited numbers of insecticides on the home/garden consumer market available for managing codling moth in home orchards. All require repeated application, timed for periods when eggs are being laid and hatching, and thorough coverage of fruit.  

Additional reading

Brunner, J. 2018. Codling Moth. Washington State University – Extension. Available https://treefruit.wsu.edu/crop-protection/opm/codling-moth/

Caprile, J., C. Costa, and P. Vossen. 2011. Codling moth. University of California Agriculture and Natural Resources. Available https://ipm.ucanr.edu/PMG/PESTNOTES/pn7412.html

Murray, M., and D. Alston. 2020. Codling Moth in Utah Orchards. Utah State University – Extension. Available https://extension.usu.edu/pests/research/codling-moth-in-Utah-Orchards#:~:text=Exclude%20codling%20moth%20larvae%20by,applied%20to%20prevent%20early%20infestation.