Larvae in Pears: Codling moth, Oriental fruit moth or something else?

Although oriental fruit moth is frequently mentioned as a pest of rising importance in pears, codling moth (CM) is an ever-present pear pest. Several samples of pears thought to be infested with oriental fruit moth (OFM) were brought to me last year and late this summer but the offending larvae turned out to be 80 - 90% codling moth. Other unwelcome pests can be found inside pears, including plum curculio grubs and lesser appleworm larvae.

Individual orchards, even though geographically close, can have very different pest pressures, so orchards need to be evaluated separately. If you suspect a problem, collect a good sized sample of damaged fruit (30 - 50 or more). Look for obvious signs of insect damage such as entry or exit holes and "frass" (insect excrement) on the fruit when sampling in the orchard. Sample fruit that have ripened early, including any in storage that ripen earlier than most. Early ripening is not a diagnostic feature of any particular insect damage; premature ripening will occur with infestation by any pest.

Codling moth and oriental fruit moth damage is usually obvious, but sometimes it is very hard to see on the exterior of the fruit. Some early ripening pears may have almost unnoticeable exterior signs of infestation, but will have extensive internal damage.

Codling moth larvae, when mature, are about twice as large as OFM larvae. Colour is not a good distinguishing characteristic between CM and OFM; CM larvae are usually a bit paler than OFM larvae but both are cream-coloured to pale pink. Look for signs of feeding on the seeds - CM larvae will often feed on seeds but OFM rarely do. Do not try to determine which pest is present by where the entrance or exit holes are on the fruit because there is too much variability in this feature. However, as a rule of thumb, OFM larvae leave by the same route that they entered the fruit more often than CM do. It's far better to base your identification by examining the actual larvae, rather than their feeding patterns.

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The best diagnostic feature to separate OFM and CM is the presence of an "anal comb" at the rear end of OFM larvae (Figure 1). On mature larvae, this feature is quite easy to see with a good 16 X hand lens or a dissecting microscope. The smaller the larvae, the harder this feature is to find and the easier it is to confuse it with the small hooks called "crochets" on the back prolegs. Unfortunately, lesser appleworm larvae also have an anal comb and are pinkish in colour. Lesser appleworm prefer apples, cherries and plums and are only occasionally found in pears. Specialists may be able to distinguish lesser appleworm larvae from OFM larvae and when uncertain, will rear the insects to adults for definitive identification.

Plum curculio grubs may also be present in pears. They are legless, white, slightly curved larvae and are easy to distinguish from the various moth larvae.

Growers need to be sure which pests are in their fruit because control programs will be different for various pests as their life cycles (peak flight, susceptible stages, etc.) vary. It's not good enough to go into a control program thinking you had 'worms' in your fruit last year - those 'worms' could have been plum curculio, codling moth, oriental fruit moth or some other insect. To control a pest properly, you first need to know what it is. Once you have it identified then you can plan a proper control strategy. Remember that spraying any product after the fruit is infested is pointless.

The best way to have larvae identified is to send them to the Pest Diagnostic Clinic in Guelph (519-767-6256). Complete information on what kind of things to send, how to package them, and a submission form is available in OMAFRA Publication 360 - Fruit Production Recommendations. Alternatively, you could have an experienced entomologist or crop consultant examine some specimens from your pears - they will have the right tools and knowledge to identify insect larvae.

Figure 1. Anal comb on rear end of oriental fruit moth larvae.
Photo: University of California - IPM for Stone Fruit Guide.

Learn more

• Pest Diagnostic Clinic
• Fruit Production Recommendations, OMAFRA Publication 360
  

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