The Codling Moth: A Global Pest

Scientific Name (Authority)	Order: Family	Common Name
Cydia pomonella (Linnaeus, 1758)	Lepidoptera: Tortricidae	Codling Moth

Codling Moth (Cydia pomonella) in Washington Apples

The codling moth belongs to the family Tortricidae, which includes over 11,000 species commonly known as “leafrollers.” Many of these species are economically important pests like the oriental fruit moth (Grapholita molesta), an orchard pest, and the spruce budworms (Choristeuna sp) that attack conifers. Leafroller moths are generally small (3 cm or less); many species are marbled brown and typically rest with their wings folded back.

The codling moth (Cydia pomonella) is one of the most destructive pests of apples (Malus domestica) worldwide. Originating in Europe, the codling moth has spread globally, particularly to regions with temperate climates, and is now found in North America, South America, Asia, Australia, and New Zealand. In North America, it was introduced over 200 years ago by early settlers (Chelan County Horticultural Pest Board).

In the Pacific Northwest (PNW), where it has been present for over a century, wild populations are prevalent. Without effective management, codling moth infestations can devastate apple orchards (PNW Pest Management Handbooks). The pest’s economic impact on the apple industry is substantial, as its larvae bore into fruits, causing direct damage, premature ripening, and reduced market value. Secondary infections by fungi or bacteria often exacerbate damage. A single larva can render an apple unsuitable for fresh market sales. Damage thresholds as low as 1% can result in rejection of fruit loads by processors or exporters.In Washington, where apple production is a $2 billion industry, codling moth infestations can lead to significant economic losses.

The codling moth’s can enter diapause during unfavorable conditions and produce multiple generations per year, making it a persistent challenge for growers. Over time, pest management strategies have evolved significantly, incorporating chemical, cultural, and biological controls. Before synthetic insecticides emerged, growers applied lead-arsenate sprays that only partially controlled the pest, causing annual crop losses of 10–25%. The introduction of DDT in 1948 and azinphos-methyl (Guthion) in the 1960s significantly improved moth control. However, as resistance developed and regulatory bodies restricted these chemicals, growers adopted integrated pest management (IPM) strategies in recent decades. The introduction of mating disruption techniques in the 1990s marked a turning point in for IPM, reducing reliance on broad-spectrum insecticides (Good Fruit Grower).

The Sterile Insect Technique (SIT) has emerged as a promising addition to codling moth management in Washington apple. orchards. SIT is a pest control method that involves mass-rearing, sterilizing, and releasing a large number of insects to reduce wild population through infertile mating. It is an environmentally friendly alternative to chemical pesticides, targeting specific pests without harming other organisms, like natural enemies. Most SIT programs for dipterans (e.g. mosquitoes and fruit flies) only release males. However, lepidopterans pests benefit from bi-sexual releases, where both sterile males and females are released. This dual-sex approach enhances the effectiveness of SIT by acting as a “mobile mating disruption” tool. The long-term success of the Sterile Insect Release (SIR) program in British Columbia, Canada underscores its effectiveness—and provides a robust model for similar fruit-growing regions in the USA. Drawing on this proven track record, M3 Agriculture Technologies refined the technique to suit local conditions, aiming to enhance apple quality and orchard profitability through an integrated, sustainable approach to pest management.

Codling moth hosts

Table 1: Codling Moth Host Preferences

Host Type	Primary/Secondary	Notes on Susceptibility
Apples (Malus domestica)	Primary	Highly susceptible; no fully resistant cultivars; variation based on skin thickness and tannin levels
Pears (Pyrus spp.)	Primary	Similar vulnerabilities to apples; key target for infestations
Walnuts (Juglans spp.)	Primary	Occasionally attacked; less prevalent than apples and pears
Quince (Cydonia oblonga)	Secondary	Infrequent infestation; can serve as a reservoir in mixed orchards
Apricots & Plums (Prunus spp.)	Secondary	Rarely attacked; supplementary hosts

Table 1: Primary and secondary hosts of codling moth. Secondary hosts, particularly in mixed orchards, can serve as reservoirs, complicating management efforts.

Notes on Host Preference or Resistance

Certain apple cultivars exhibit varying levels of susceptibility to codling moth. For example, cultivars with thicker fruit skins or higher levels of natural tannins may deter larval penetration. However, no commercially grown apple variety is entirely resistant.

Life stages / Life history

Egg Development and Hatching

Codling moth eggs are deposited by females during the early stages of their reproductive cycle. Eggs are laid primarily during warm evenings when temperatures exceed 60°F (15.5°C). The incubation period for eggs is temperature-dependent, typically lasting 6–20 days. Warmer conditions accelerate development, with eggs hatching faster during mid-summer compared to cooler spring conditions.

Eggs are highly vulnerable to environmental factors, including desiccation and predation by natural enemies such as predatory mites. This vulnerability underscores the importance of monitoring egg-laying periods to time control measures effectively. Pheromone traps and degree-day models are critical tools for predicting peak egg-laying periods (WSU Tree Fruit).

Larval Feeding and Damage Progression

Upon hatching, neonate larvae immediately seek out fruit, often targeting the calyx or stem end. They burrow into the fruit, creating entry holes that exude frass (insect excrement). Inside the fruit, larvae tunnel toward the core, feeding on seeds and surrounding tissue. This internal feeding renders the fruit unmarketable and often leads to secondary infections by fungi and bacteria, further exacerbating losses.

Larvae pass through five instars during their development, growing from approximately 1 mm to 20 mm in length. The feeding period lasts 3–4 weeks, after which mature larvae exit the fruit to pupate. In Washington, fruit damage is most severe during the second and third generations, which coincide with peak harvest periods for many apple varieties (Good Fruit Grower).

Pupation and Overwintering

Mature larvae exit the fruit and seek sheltered locations for pupation, such as under loose bark, in soil crevices, or within orchard debris. Pupation typically lasts 10–14 days during the growing season but is extended for overwintering larvae, which enter diapause to survive cold winter conditions. This stage is critical for survival during Washington’s cold winters. The duration of diapause can vary based on regional climate and orchard management practices.

Overwintering larvae are highly resilient, with survival rates influenced by environmental factors such as temperature and moisture. Studies have shown that larvae can survive temperatures as low as -20°F (-28.9°C) when adequately insulated by bark or soil. This resilience makes overwintering larvae a critical target for cultural control measures, such as removing orchard debris and using trunk banding to capture larvae before pupation (WSU Tree Fruit).

Adult Emergence and Mating Behavior

Adult codling moths emerge in spring, with the timing dictated by degree-day accumulations. In Washington, the first generation typically emerges at 250–300 degree-days (base temperature 50°F). Males locate females using sex pheromones, which are emitted by females to attract mates. Mating occurs primarily during dusk when temperatures exceed 58°F (14.4°C).

Females begin laying eggs 2–3 days after mating, with each female capable of producing 50–100 eggs over her lifetime. Mating disruption techniques, such as pheromone dispensers, exploit this behavior by saturating the orchard with synthetic pheromones, confusing males and reducing successful mating events (Good Fruit Grower, Codling Moth Management and Chemical Ecology).

Generational Overlap and Regional Variations

In Washington, codling moth typically completes two to three generations per year. The first generation emerges in late spring, while subsequent generations occur in mid-summer and early fall. The first generation usually coincides with apple bloom. The exact timing is temperature-dependent and is often predicted using degree-day models. In warmer regions of Washington, such as the Yakima Valley, codling moth populations may produce a partial fourth generation during extended growing seasons. This generational overlap complicates management, as larvae from multiple generations may be present simultaneously, requiring continuous monitoring and treatment.

In cooler regions, such as higher-elevation orchards, codling moth development is slower, with only two generations per year. These regional differences highlight the importance of localized degree-day models and phenology tracking to optimize control strategies (WSU Tree Fruit).

Table 2: Codling Moth Life Stages Overview

Life Stage	Key Characteristics	Location/Behavior
Egg	Oval, flat, ~1 mm; laid singly on leaves, fruit, or bark	Typically on upper leaf surfaces near developing fruit
Larva	Cream-colored with a black head capsule; grows to 12–20 mm; bores into fruit	Feeds inside fruit, creating entry holes and frass deposits
Pupa	Brown, ~10 mm; encased in a silken cocoon	Found under loose bark, in soil, or among orchard debris
Adult	Gray with dark wavy lines and a copper band; 15–20 mm wingspan	Active at dusk; strong fliers capable of dispersing several kilometers

Table 2: Developmental stages must be identified by growers for management efforts.

Monitoring methods & tools / Treatment thresholds

Growers in Washington use the WSU Decision Aid System (DAS) to access real-time degree-day data and management recommendations. This system integrates weather data with pest models to provide actionable insights, such as the optimal timing for pheromone dispenser deployment or insecticide applications (WSU DAS). Tools like the WSU Decision Aid System provide access to degree-day models, enabling growers to optimize spray timing and reduce unnecessary applications. Degree-day models predict codling moth development based on accumulated heat units.

Key Degree-Day Benchmarks:

Biofix: The first sustained moth capture in pheromone traps marks the start of degree-day accumulation.
Egg Hatch: Begins at approximately 250 degree-days after biofix.
Larval Peak Activity: Occurs around 500-600 degree-days.

First-generation moth emergence: 250–300-degree days (base 50°F). First egg hatch: 375-degree days. Second-generation moth emergence: 1175-degree days. Second egg hatch: 1400-degree days (WSU Tree Fruit).

Growers in Washington use the WSU Decision Aid System (DAS) to access real-time degree-day data and management recommendations. This system integrates weather data with pest models to provide actionable insights, such as the optimal timing for pheromone dispenser deployment or insecticide applications (WSU DAS).Tools like the WSU Decision Aid System provide access to degree-day models, enabling growers to optimize spray timing and reduce unnecessary applications.

Damage is assessed by visually inspecting fruit for entry holes, frass deposits, and internal feeding tunnels. Sampling protocols involve inspecting 30–40 fruit per tree across multiple trees in an orchard. Damage is often concentrated in the upper canopy, where larvae are less exposed to natural enemies and insecticide sprays. Accurate damage assessment is critical for determining the effectiveness of control measures and adjusting management strategies (WSU Tree Fruit).

Pheromone traps are widely used to monitor adult male populations. These traps contain synthetic female sex pheromones that attract males, providing an indication of moth activity and population density. Traps are deployed before the first expected moth flight, typically in early spring. They are placed at canopy height with at least one trap per 2.5 acres in orchards using mating disruption and higher densities in untreated orchards. Traps are used in conjunction with degree-day models to predict egg hatch and larval activity. This helps growers time interventions more effectively.

In Washington, economic thresholds are typically set at 1-2% fruit damage. Exceeding these levels prompts intervention to prevent further losses. Action thresholds vary but generally range from 5-10 moths per trap per week in untreated orchards. A consistent weekly catch of 2-3 moths per trap may indicate the need for supplemental insecticide applications.

Table 3: Monitoring Methods and Treatment Thresholds for Codling Moth

Monitoring Method	Key Approach	Threshold/Timing
Degree-Day Models	Calculate accumulated heat units to predict development stages	Egg hatch ~250 DD; larval peak at 500–600 DD
Visual Inspections	Regular checks of fruit and foliage for eggs, larvae, and damage	Focus on upper canopy; sample 30–40 fruits per tree
Pheromone Traps	Use synthetic pheromones to attract male moths	5–10 moths per trap per week in untreated orchards; 2–3 in mating disruption areas

Table 3: Monitoring techniques and associated treatment thresholds provide growers with actionable data for timely interventions.

Management Strategies for Codling Moth in Washington Apple Orchards

Integrated Pest Management (IPM) Framework

Environmental factors, such as orchard sanitation and weather conditions, play a significant role in codling moth dynamics. For example, wet conditions during the growing season can increase fungal infections in damaged fruit, while dry conditions may reduce egg survival. Integrated pest management (IPM) strategies that combine cultural, biological, mechanical, and chemical controls are essential for minimizing these secondary impacts while reducing environmental impact (Plantwise Knowledge Bank).

Sterile Insect Release (SIR)

The Sterile Insect Release (SIR) program is an emerging strategy in Washington. This method involves releasing mass-reared, sterilized codling moths into orchards to reduce wild populations through unsuccessful mating. Between 2017 and 2020, Washington State University (WSU) conducted trials to assess the feasibility of SIR in local orchards (WSU IPM).

Key findings from these trials include:

Baseline trap captures indicated that SIR could significantly suppress codling moth populations in isolated orchards.
SIR is most effective when used in the context of Integrated Pest Management to reduce initial pest densities.
Challenges include ensuring synchronization of sterile moth releases with wild moth emergence and maintaining the fitness of released insects.

Mating Disruption Techniques

Mating disruption (MD) uses synthetic pheromones to confuse male moths, preventing them from locating females and reducing successful mating events. Pheromone dispensers, such as hand-applied dispensers, puffers, or aerosol emitters, are deployed early in the season, typically at 100-degree days (base temperature 50°F), before the first generation of moths begin mating.

Research demonstrates MD is most effective when combined with other control measures, such as insecticides or biological agents, to address residual populations in high-pressure areas.

Chemical Control Strategies

Chemical control remains a critical component of codling moth management, particularly in high-pressure orchards or when other methods are insufficient. However, reliance on chemical insecticides has decreased due to resistance development and regulatory restrictions on broad-spectrum products like azinphos-methyl (Guthion).

Targeted Insecticide Applications

Modern chemical control strategies emphasize targeted applications based on degree-day models and pest monitoring data. For example:

The first spray is typically applied at 250-degree days after biofix (the date of first moth capture in pheromone traps) to target newly hatched larvae before they enter the fruit (Good Fruit Grower).
Subsequent sprays are timed at 1250-degree days for the second generation, with additional treatments guided by trap counts and fruit inspections.

Insecticides used include ovicides (e.g., novaluron) to target eggs and larvicides (e.g., spinosad) to control neonate larvae. To prevent resistance, growers rotate products with different modes of action, following guidelines from the WSU Crop Protection Guide (WSU Tree Fruit).

Reduced-Risk Pesticides

Washington growers increasingly adopt reduced-risk pesticides, such as codling moth granulovirus (CpGV) and insect growth regulators (IGRs), to minimize non-target impacts and align with sustainable practices. CpGV is highly specific to codling moth larvae and can be applied multiple times during the season, particularly in organic orchards. However, its effectiveness may be limited by high population densities or UV degradation, requiring frequent reapplications.

Cultural and Mechanical Controls

Cultural and mechanical controls are essential for reducing codling moth populations and complementing other management strategies. These methods focus on disrupting the pest’s life cycle and reducing overwintering sites.

Orchard Sanitation

Orchard sanitation practices, such as removing fallen fruit and pruning infested branches, are critical for reducing overwintering larvae. Studies show that eliminating fruit drops can reduce codling moth populations by up to 30% (Montana State University). Additionally, shredding or burying pruned branches can destroy pupae hidden under bark.

Tree Banding and Trunk Barriers

Tree banding with corrugated cardboard strips is a mechanical method used to capture larvae migrating down the trunk to pupate. These bands are removed and destroyed before adult emergence in spring. Trunk barriers, such as sticky bands or netting, can also prevent larvae from reaching pupation sites, further reducing overwintering populations.

Biological Control

Biological control agents, such as Trichogramma wasps and codling moth granulosis virus (CpGV), are increasingly used in Washington orchards. Codling moth infestations can lead to increased pesticide use, which may disrupt beneficial insect populations and contribute to resistance development. Conserving natural enemies through reduced pesticide use and habitat enhancement can improve biological control, creating a more sustainable IPM framework (WSU Tree Fruit, USDA ARS).

Environmental factors, such as orchard sanitation and weather conditions, play a significant role in codling moth dynamics. For example, wet conditions during the growing season can increase fungal infections in damaged fruit, while dry conditions may reduce egg survival. Integrated pest management (IPM) strategies that combine cultural, biological, and chemical controls are essential for minimizing these secondary impacts (Plantwise Knowledge Bank).

Biological control agents:

Parasitoids: Trichogramma minutum Mastrus ridibundus, M. ridensand Ascogaster quadradentata are notable parasitoids of codling moth eggs and larvae. Field studies indicate that parasitism rates can exceed 40% in orchards where these wasps are established (USDA ARS).
Predators: Generalist predators, such as lacewings and spiders, contribute to natural control.
Pathogens: Codling moth granulovirus (CpGV) is a widely used microbial control agent in Washington. It is highly virulent and specific to codling moth larvae, making it an ideal choice for organic orchards. Entomopathogenic nematodes (EPNs), such as Steinernema feltiae, are another option for targeting overwintering larvae in soil or bark crevices. However, EPNs require adequate moisture and temperatures above 10°C to remain effective (USDA ARS).

Biological control agents, such as Trichogramma wasps and codling moth granulosis virus (CpGV), are increasingly used in Washington orchards. These agents are most effective when combined with cultural practices and reduced pesticide use, creating a more sustainable IPM framework (WSU Tree Fruit, USDA ARS).

Table 4: Integrated Pest Management (IPM) Strategies for Codling Moth

Strategy	Proposed Change/Approach	Expected Outcome
Sterile Insect Release	Release mass-reared sterile moths to interfere with reproduction	Suppress wild populations when integrated with other controls
Mating Disruption	Deploy synthetic pheromones early in the season (around 100-degree days)	Reduce successful mating; lower overall population density
Targeted Insecticide Applications	Time sprays using degree-day models (first at ~250 DD)	Minimize larval survival; rotate products to prevent resistance
Cultural & Mechanical Controls	Implement orchard sanitation, tree banding, and trunk barriers	Reduce overwintering sites; lower pest pressure
Biological Controls	Utilize natural enemies (e.g., parasitoids) and CpGV	Enhance control through environmentally friendly measures

Table 4: Key IPM strategies for codling moth management and anticipated benefits for sustainable control in apple orchards.

The codling moth granulovirus (CpGV) is a widely used microbial control agent in Washington. It is highly virulent and specific to codling moth larvae, making it an ideal choice for organic orchards. Entomopathogenic nematodes (EPNs), such as Steinernema feltiae, are another option for targeting overwintering larvae in soil or bark crevices. However, EPNs require adequate moisture and temperatures above 10°C to remain effective (USDA ARS).