Even though apple maggot flight is not particularly strong in most N.Y. orchards this season, we are entering the traditional period of peak emergence. Following is some general information on the biology and life history of this well-known insect.

The apple maggot overwinters as a pupa in the soil. Adults from the single generation of flies begin to emerge in late June to early July. Females cannot lay eggs until they become reproductively mature, 7-10 days after emergence. Females lay eggs in fruit and larvae develop there, emerging in the autumn after the fruit has fallen and entering the soil to pupate. Flies are active from July to mid-September, but commercial orchards generally require protection only from about mid-July through August. Flies do not reach orchards in large numbers until mid-July, and before this date fruit remaining on the tree is unfavorable for larval development, so early infestations do not cause sustainable populations in the orchard. In addition, for unknown reasons, fly activity between about August 20 and September 15 does not usually cause serious damage in commercial orchards in New York.

Larval tunneling inside the fruit causes it to become rotten and unmarketable. Early stings caused by punctures from the female's ovipositor may severely deform the fruit of some varieties, even though no larvae survive.

Monitoring to determine whether control sprays are necessary is recommended primarily in orchards that are not near large sources of outside infestation (such as abandoned orchards), and those with no indigenous infestations of flies. Theoretically, there is absolutely no tolerance for AM damage in fruit. In practice, AM damage is not usually detected in normal fruit inspections unless there is approximately 5 percent fruit damage.

Small wasps parasitize AM larvae in fruit, and predators such as birds and crickets may eat larvae or pupae in or near the soil. In natural, unsprayed apple and hawthorn trees, AM populations are not regulated by natural enemies. Parasites and predators are also ineffective at controlling AM in commercial orchards.

AM flies have a limited migratory capability, so all apple and hawthorn trees within 1/4-1/2 mile of commercial orchards should be removed if possible. Do not allow dropped fruit to remain beneath the tree for more than one to two days. Eliminating fruit drops will break the life cycle of flies in an orchard by preventing larvae from exiting the fruit and entering the soil.

AM flies can be "trapped out" in small, well-pruned trees that are not near large sources of outside infestations. A relatively high density of sticky red spheres (plain or volatile-baited) is required, approximately 1 trap per 100 apples. Mass trapping is usually less effective than chemical control, and AM may still damage 1-5% of fruit from mass-trapped orchards.

Most commercial orchards have no indigenous populations of flies. Therefore, chemical control sprays are usually directed against flies immigrating into orchards from outside, unsprayed hosts, including both apples and hawthorns. Most insecticides, particularly organophosphates, are remarkably effective in controlling adults. Insecticides must kill females before they oviposit in the fruit. Residual effectiveness of insecticides is particularly important in controlling AM in commercial orchards when flies are continuously immigrating.

Insecticides can be applied according to trap catches as described in the 1997 Pest Management Recommendations for Commercial Tree-Fruit Production (p. 84), or on a standard or modified IPM schedule. The standard schedule requires an initial spray 7-10 days after the first emergence of flies, followed by additional sprays at 10-14-day intervals until August 15-20. (The first AM fly in Geneva was trapped on 7/7.) The modified IPM schedule requires only three sprays, on approximately July 15, August 1, and August 15. We would suggest that growers in high maggot-pressure areas maintain a standard spray schedule, or at least be vigilant in checking traps twice a week, in order not to be caught unprotected during this peak flight period.

A few words may be in order here about when to terminate sprays for apple maggot in late summer. Most people are aware that each year in N.Y. orchards, substantial numbers of AM flies are captured on monitoring traps late in the season, and growers are naturally concerned about potential fruit infestation from these late season survivors. For the past few years, we have conducted trials in a heavily infested research orchard of McIntosh and Cortland trees by applying bi-weekly applications of Guthion beginning in early July and continuing for 2, 3, 4, and 5 total sprays.

New oviposition punctures were checked weekly on "scout" apples clipped to the trees, and female AM flies captured throughout the flight period were dissected to check for the presence of eggs. The results of these studies can be summarized as follows:

1) Gravid female flies were present in the orchards in September and October.

2) Although peak oviposition times varied among apple varieties from year to year, only trace amounts of oviposition occurred in September.

3) AM fruit damage in the unsprayed check trees was substantial in both varieties (between 20-45%), with higher damage levels occurring in the Cortland apples. However,

4) There was no statistical difference in fruit damage among any of the treatments regardless of spray termination date, which ranged from August 3 to September 7.

We regard these results as corroboration of our long-standing recommendations that a final spray be applied around the middle of August to effectively control apple maggot in most commercial orchards.