Codling Moth

The codling moth is so pervasive that it is stereotypically called the “apple worm”, leading to the common phrase “wormy apple”.

Codling moths are a major pest of apple and pear orchards. Caterpillars will bore into fruit which leads to premature ripening and inedible fruit. Without intervention, codling moths can infest 20-90% of a fruit tree. In warmer conditions, codling moths can have up to five generations in a season and caterpillars are able to enter a diapause state to survive poor fruiting seasons or cold winter temperatures. 

Codling Moth Species, Types, and Scientific Name

There is only one species of codling moth. Its scientific name is Cydia pomonella. Pomonella is derived from Pomona, the Roman goddess of fruit trees. The Genus name Cydia is familiar to iOS users as the popular application able to download software not authorized by Apple Inc. A metaphorical worm in Apple Inc’s products.

Appearance: How To Identify Codling Moths

Adult codling moths are rather nondescript with mottled grey wings held tentlike above their bodies. The mottling acts as camouflage, allowing adults to blend with most tree bark. They average ½” to ¾” in size. Males will have a shiny copper band at the end of their wings. 

Eggs are disc-shaped and roughly 1-1.2 mm. As the egg matures, a red ring forms followed by a red dot where the caterpillar head is. When it hatches, the caterpillar is about 2 mm long, 0.5 mm in diameter, and white with a dark brown head. As the caterpillar matures through five instars, it will grow to 12-20 mm long and have a pinker appearance. A fully grown codling moth caterpillar will be light pink to light brown with dark brown spots along each segment and a dark brown or black head capsule. 

Codling moth pupae are brown and 12mm long on average. First-generation caterpillars will spin a cocoon of finer silk while second-generation caterpillars will spin a coarser cocoon that incorporates wood bark. 

Female codling moths will oviposit 30-70 eggs individually on the fruit, nuts, leaves, or branches of the host fruit tree. While they’re capable of long-distance flight, up to several kilometers, a majority of adult codling moths remain sedentary. Adult moths are only active for a few hours before and after sunset. They prefer to mate during sunset when it is warmer than 62ºF. 

Caterpillars are somewhat unique Lepidopteran juveniles in that they will bore into the flesh of fruits rather than feed on leaves. To survive the winter or years with poor fruit yield, caterpillars are able to enter a state of decreased activity (diapause) and resume activity when temperature or food sources are more favorable.

Habitat: Where to Find Codling Moths

Codling moths are found everywhere apples are grown, even on solitary trees in urban environments. Adults can be found on branches or the underside of leaves of the host tree while caterpillars will be found inside the flesh of the fruit.  

After the fifth instar, the codling moth caterpillar will drop from the fruit and search for a suitable place to pupate. Most will remain in the soil while some spin a cocoon in the crevices of the tree’s bark. 

While codling moths are found on every continent, it is believed they were native to Asia Minor and were introduced to Europe centuries before they were discovered. They were introduced to North America during the Colonial Period and expanded their habitat to the Pacific coast by 1872. 

Diet: What do Codling Moths Eat?

What do Codling Moths Eat?

Juvenile codling moths are a voracious pest of apple orchards. If left unchecked, they can damage anywhere from 20-90% of the fruit on a single tree. While apples are their preferred food, codling moths are also a pest of pear, walnut, apricot, peaches, plums, cherries, and chestnuts. After emerging from the egg, caterpillars will enter the fruit and tunnel to the center, leaving a hole in the fruit, filled with reddish-brown frass (poop). While there, they will continue to eat and molt through five instars before dropping to the ground to spin a cocoon. 

Adult codling moths rarely eat even though they are able to. Feeding does not affect the adult’s ability to mate and oviposit. 

What eats Codling Moths?

Woodpeckers are the #1 predator of codling moth larvae and will feed as the caterpillars leave the fruit or when caterpillars are in their cocoons. Nuthatches and creepers are also significant predators of codling moth caterpillars. 

A number of arthropods will prey on codling moths, including spiders, harvestman, beetles, earwigs, and ants. Ants will attack all life stages while the other arthropods will generally prey on only the juvenile or adult stages. 

Two species of thrip will prey on codling moth eggs. Haplothrips faurei are nondiscriminant and will prey on eggs from any generation while Leptothrips mali prefers second-generation eggs. 

Prevention: How to Get Rid of Codling Moths

It is almost impossible to completely prevent a codling moth infestation. Instead, growers should focus on monitoring to catch populations early on and implement control. 

Pheromone traps placed during the pink stage of apple flower-bud development can be used to monitor for adult male codling moths. The process of banding trees has been used to monitor for caterpillars. A strip of cardboard is affixed to the trunk of the tree. The mature larvae will then spin their cocoons inside of the cardboard. Both pheromone traps and banding can be used to detect and then estimate the density of codling moth infestations. 

Beginning as early as July, growers should visually assess fruit for codling moth damage. Codling moth caterpillars prefer fruit in the top half of the tree, so sampling of fruit in that area is most effective. 

Treatment Thresholds: When to Control Codling Moths

There are two threshold-based methods one could use to determine when to implement control: damage to fruit and trap capture. 

When visually inspecting fruit, if fruit injury levels are greater than 0.5% of the total yield, it is time to consider a control method for codling moths. Trap methods are a little more complicated but usually require less time and energy to monitor. Deploy one pheromone trap for every 2.5 acres and check traps once a week after the first moths are caught. Replace the trap after 30 moths have been caught or if the trap becomes dirty. 

Thresholds for control using pheromone traps can be set in one of two ways. For the first method, the threshold is set when two moths are caught in two consecutive weeks. The second method involves degree days, which can be calculated here. If 5 or more moths are caught between 175 and 425 degree days, then a control method should be implemented. Second-generation codling moth thresholds are reduced to 3 moths before a treatment plan is implemented starting on the 1175th-degree day. 

Management: How to Control Codling Moths

There are several organic ways to control for codling moths before resorting to pesticides, although most integrated pest management strategies recommend using them in conjunction with a conventional insecticide.

• Choose resistant varieties, such as early-maturing apples and pears, and late-leafing walnuts. 
• Sanitation, or the process of removing and destroying any fruit that shows signs of codling moth caterpillar damage. This should be done every 1-2 weeks roughly 6-8 weeks after the first bloom. 
• Bagging fruit is the best nonchemical option for small orchards. Young fruit is enclosed in a paper bag to prevent codling moth caterpillar from entering the fruit. Beginning 4-6 weeks after first bloom or when the fruit is ½” – 1” in diameter, cut a 2” slit in the bottom of a standard paper lunch bag. Thin the fruit to one per cluster and slip the paper bag over the fruit, creating a seal at the stem. Staple the bag shut. 
• Mating disruption involves applying a pheromone to crops that disrupts or delays the male codling moths’ ability to find and mate with females, reducing the number of offspring for that generation. 
• Walnut and pear orchards can utilize the parasitoid wasp, Trichogramma platneri, in combination with mating disruption or pesticides. This small wasp oviposits in the codling moth egg and the wasp larvae feed on the undeveloped caterpillar. The wasp will then pupate inside the codling moth egg and emerge, effectively killing the codling moth before any damage can be done. 
• Codling moth granulosis virus (CYD-X) is a biological insecticide that does not affect other arthropods, humans, pets, or wildlife. After ingesting the virus, codling moth caterpillars die of the disease in 3-7 days. CYD-X is as effective as conventional insecticides when applied weekly. 
• Spinosad is a biocontrol product derived from the bacteria Saccharopolyspora spinosa. While safe for people, pets, and the environment, it is slightly toxic to beneficial insects. 

Carbaryl is a broad-spectrum insecticide that is effective against codling moths but with significant disadvantages. It is toxic to natural predators and honey bees, so should not be applied when fruit trees are in bloom. Spraying within one month of bloom may cause fruit to drop. More than one application of carbaryl may also cause an outbreak of pest mites. 

Carbaryl has been linked to water quality problems. Nonchemical pest management strategies should be considered before the use of this insecticide. 

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