Control of codling moth (Cydia pomonella ( L.)) is the key to almost all other pest programs in pome fruit orchards. Some of the chemicals registered to control codling moth have adverse effects on beneficial insect species, which contribute to biological control of other pests. Use of such disruptive chemicals often results in the need to apply more pesticides for control of minor pests.
Description of life stages
The adult codling moth has a wingspan of about 12 to 18mm and is about 10mm long when at rest with the wings folded (Figures 1 and 2).
Males are smaller than females. The forewings are brownish grey with several grey crosslines. An iridescent coppery-brown spot is present near the tip of each forewing. The hind wings are pale brownish-grey with fringed borders. At rest the codling moth has its wings folded behind its back (Figure 3).
The female moth lays eggs singly on leaves and fruit. The egg is flat, oval, 1mm long, opaquely white when first laid and develops a red ring towards maturity. Just before hatching the black head of the larva becomes visible in the egg.
A newly hatched larva is white with a black head. There are generally 5 larval stages, which can be identified by the width of the head. Average widths of larval head for the 5 stages are approximately 0.3, 0.5, 0.8, 1.2 and 1.7mm respectively.
Fully mature larvae are about 15mm long and creamy pink with a dark brown head. They leave the fruit and form cocoons under loose bark on the tree or amongst leaf litter on the ground beneath the tree. In summer most of the cocooned larvae form a pupa from which the adult moth emerges about 2 weeks later. A small percentage of the cocooned larvae in summer enter diapause (become dormant) until the following spring. As day length decreases towards autumn a higher percentage of cocooned larvae enter diapause and all of the larvae that cocoon in autumn enter diapause.
Young larvae chew through the fruit skin and excavate a cavity just below the skin where they moult before starting to bore their way to the core (Figure 4).
At the core they feed on the seeds. The presence in fruit of one or more holes plugged with frass (excrement) is characteristic of attack by codling moth (Figure 5). The larvae enter the fruit through the sides, stem or calyx end and a syrupy substance may exude from the holes as the fruit matures. Similar damage can be caused by oriental fruit moth where pome fruit is grown near stone fruit but oriental fruit moth generally do not feed on the seeds.
Shallow entries called 'stings' result when larvae die from insecticide poisoning or natural causes while excavating the cavity below the skin (Figure 6).
Some of the overwintering larvae start to pupate early in spring, if they have experienced enough winter chill, as temperatures increase. This first cohort of the overwintered population begins to emerge as moths about the time of bloom. The moths emerge usually in one or more periods of peak activity, each period referred to as a 'flight'. A second cohort of the overwintered population starts to pupate when the day length increases to around 14 hours and begin to emerge as additional flights of moths a few weeks later depending on daily temperatures. Eggs laid during these flights give rise to the first generation of the new season. Adults of the first generation produce the second generation. Up to 3 generations per season may occur in Victoria, depending on prevailing weather conditions. The first and second generations include the progeny of both cohorts as distinct but overlapping populations but generally the third generation only includes progeny of the first cohort of the second generation.
A varying proportion of mature larvae from the second generation enter diapause instead of emerging as adults during the current season. The proportion of larvae entering diapause depends on the temperature conditions during the season and the decreasing day length. All of the larvae in the third generation enter diapause after they leave the fruit and establish cocoons. Larvae that enter diapause spin cocoons within which they survive the winter.
Effect of temperature on codling moth
The body temperature of insects is closely related to the temperature of the surrounding environment. The growth of an insect increases as temperature increases until the optimum temperature for the particular type of insect is exceeded; at this point the growth rate rapidly declines. The temperature below which the growth of a given type of insect is assumed to be zero is called the lower developmental threshold.
The lower developmental threshold for codling moth is 10°C. When temperature is traced through a series of days and compared to an insect's lower developmental threshold the amount of its growth on any given day can be estimated and converted to physiological time units called degree-days.
It is important to note that physiological time varies from day to day but chronological time is constant. The eggs, larvae and pupae of codling moth each have specific physiological time requirements to complete development before they transform to the next stage. Temperature also affects the flight, mating and egg laying activities of the adults. Although the minimum threshold for emergence of moths is 10°C, male moths do not fly until temperatures exceed 13°C and codling moths do not mate until temperatures exceed 16°C .
Adult female codling moths release a sex-attractant chemical (pheromone) to attract male codling moths. Synthetic pheromones are used in traps to indicate the presence of male codling moths in orchards. Pheromone-trap catches and temperature records can be used to predict when the eggs resulting from a particular moth flight will be hatching. Such predictions allow better timing of spraying. Traps containing a combination of pheromone and host plant volatiles are also available and attract both sexes, which is useful for monitoring moth activity when mating disruption products are in use.
Biological and cultural control
Mating disruption is a technique in which the orchard air is saturated with pheromone emitted from slow-release dispensers. This disrupts moth communication and makes it difficult for male moths to locate and mate with the females. Mating disruption products are available commercially for large-scale orchards and, although they do not entirely eliminate mating, they do delay it and reduce the number of eggs being laid.
Codling moth eggs are preyed on by earwigs and mirid bugs but neither gives significant control. Wasps such as Trichogramma parasitize codling moth eggs and have been used with some success in Russia. Under Australian conditions, the rate of parasitism is too low for commercial use as a stand-alone treatment but research is underway to integrate egg parasitism with other biological control options.
Removal of over-wintering sites by scraping loose bark from trees and maintenance of general orchard hygiene may help to reduce the survival of over-wintering populations. Similarly, provision of artificial cocooning sites such as bands of cloth or corrugated cardboard wrapped around the trunks allows overwintering larvae to be trapped and destroyed but if not done properly can enhance survival of overwintering larvae. These methods are generally too time consuming and expensive for adoption by commercial growers.
A parasitoid wasp, Mastrus ridens, that attacks codling moth larvae in their cocoons has been introduced and released into commercial orchards with promising results. This wasp is particularly effective at reducing overwintering populations of cocooned larvae. A parasitic nematode has also shown promise for control of overwintering larvae and is available as a commercial product.
Codling moth larvae are susceptible to infection by a virus when they are stressed. The virus is available as a commercial product but timing of application is critical because the larvae have to ingest the virus and the only time the larvae are exposed to it is when they hatch from the egg and walk across a treated leaf or fruit surface on their way to a feeding site. It usually takes several seasons of persistent use, usually in combination with other treatments, to bring the codling moth population down to commercially acceptable levels. Since the larvae have to ingest the virus before it can infect them, they have to take it in while feeding and because it takes a while to kill them some feeding damage ('stings') occurs.
Chemical control is often one of the methods available for plant pests as part of an integrated pest management program. Further information is available from your local nursery, cropping consultants, chemical resellers and the pesticide manufacturer. For information on currently registered and or permitted chemicals, check the Australian Pesticide and Veterinary Medicine Authority (APVMA) website and always consult the label and Safety Data Sheet before using any chemical product.
- Todd M Gilligan and Marc E Epstein TortAI Tortricids of Agricultural Importance USDA APHIS PPQ Bugwood.org
- Todd M Gilligan and Marc E Epstein TortAI Tortricids of Agricultural Importance. USDA APHIS PPQ Bugwood.org
- Whitney Cranshaw, Colorado State University, Bugwood.org
- Ross Courtney
- Whitney Cranshaw, Colorado State University, Bugwood.org
- Ward Upham, Kansas State University, Bugwood.org