There is one main generation per annum in the UK with a partial second generation in late August and September. The second generation is more marked in hot years which favour rapid development of the first generation.
- Larval development has seven instar stages.
- The pest overwinters mainly as a third, sometimes second, instar larva in a silken hibernaculum beneath a bud scale, between a dead leaf and a twig or spur or in crevices in the bark or other shelter.
- After emergence in spring, shortly after bud-burst, individual larvae feed in or amongst the buds, often tying them and rosette leaves together with webbing.
- Fifth instar larvae feed on developing fruitlets, making cavities in the receptacle, which later heal to form corky scars characteristic of early caterpillar feeding.
- Sixth and seventh instar larvae tend to live on foliage.
- Larvae pupate when fully fed, normally in late May or early June.
- First generation adult moths emerge three weeks later, normally in late June and early July, and often a week or two after the flight of codling moth has exceeded the threshold.
- Eggs are laid in batches on the foliage. These hatch in 2-3 weeks depending on temperature (see ‘Forecasting’ below).
- Cool and wet weather conditions at the time of moth flight and/or during egg-hatch limit population increase.
- The tiny first instar larvae spin webs of silk, usually on the undersides of leaves close to the veins leaves, often at a junction between the main and a side vein, and begin to feed.
- They feed on leaves, often between two spun leaves or where two or more fruits are touching or in the calyx cavities of fruits.
- A greater proportion of third instar larvae feed on fruits. Most larvae overwinter in this third instar stage.
- A proportion of more advanced larvae complete their development in August and a partial second generation of adults occurs in August and September.
- These hatch in September or early October and the young larvae feed on leaves overwintering if they reach the second or third instar development stage.