Apple maggot—Rhagoletis pomonella
Apple maggot is native to the northeastern United States and Canada. It was not discovered attacking apples until about 100 years after trees were introduced from Europe. It is now considered a major pest of apples in several apple-growing regions because it directly damages the fruit. Apple maggot is currently established only in northern California from Sonoma County north. It is established in Del Norte, Siskiyou, Humbolt, Trinity, Shasta, and Sonoma counties in California. Please report sightings in other counties to your county agricultural commissioners.
Identification of species
Adult maggots have clear wings with black bands, a pronounced white spot on the back of the thorax, and a black abdomen with light crossbands. Females have four crossbands on the abdomen; males have three. Apple maggot is closely related to walnut husk fly and cherry fruit fly. It can be distinguished from these other pests by the banding on its wings.
Apple maggots overwinter as pupae in the soil. Generally there is one generation a year, although there may be a partial second generation in warm years. Adults emerge in mid-June to early July; emergence usually peaks between mid- and late July and is over by late August. In some places, some of the pupae may remain in the soil and will not emerge until the following year.
When flies emerge in summer, they are sexually immature and must feed on honeydew produced by aphids, psyllids, and scales before they are ready to mate. Female flies lay eggs singly under the skin of apples and then mark the apple with a pheromone to keep other females from laying eggs. Females lay about 300 eggs over a 30-day life span. Eggs hatch in 2 to 10 days, depending on temperature. Larvae are cream colored with a blunt posterior and a tapered front end that contains two black mouth hooks. They feed within the apple and pass through three instars before completing developing in 20 to 30 days. Infested fruit fall to the ground; larvae leave the fruit, burrow into the soil, and molt into a fourth instar and then into a pupal stage to overwinter.
In soft-fleshed apple varieties a small, dark, decayed spot occurs at the oviposition site. In hard-fleshed varieties, the oviposition site results in a dimple. Young larvae tunnel throughout the apple flesh, leaving a small, brown, irregular, threadlike trail. The tunnels enlarge as the larvae grow; eventually decay organisms enter the fruit and cause internal rotting and fruit drop.
Sanitation is very important in controlling apple maggot. Clean up fallen fruit and discard. To detect presence of adults, hang yellow sticky traps in trees; traps attract flies in search of food. If you find apple maggot in counties where it has not been reported, contact your local Agricultural Commissioner's Office or UC Cooperative Extension office. Sticky red sphere traps hung in trees can help control maggots. Applications of spinosad made mid-July and repeated every 7 to 10 days if necessary can also help control this pest.
flies; male (left) and female (right)
Decayed areas indicate egg-laying sites
Maggot larvae tunneled into apple flesh