The olive fruit fly (Bactrocera oleae) is the most serious pest for olives. It is widely distributed from the Canary Islands to India and common throughout the Mediterranean region. The olive fruit fly was introduced into California in the late 1990s and is now causing extensive damage there as well.
Life cycle and appearance of Olive fly
The adult olive fruit fly is about 4-5 mm long. Its head, thorax, and abdomen are brown with darker markings and several white or yellow patches on the top and sides of the thorax. The wings are transparent, with dark veins, positioned horizontally, and are held away from the body. Eggs are laid in the olive fruits and are 0.7-0.8 mm long and white and opaque. Larvae are yellowish white, legless maggots, up to 7 mm long with pointed heads. After hatching, the larvae immediately start to tunnel within the fruits. They are tiny and difficult to see. After they have been feeding for a while, they are easier to locate, especially when the fruit has begun to rot. The puparium is 3.5-4.5 mm long and yellowish brown.
In the field, olive fruit fly development, and the resulting number of annual generations, are not only dependent on ambient temperature, but also on humidity and microclimate within the olive canopy, and on the availability and quality of the olive fruit.
In most regions, the olive fruit fly appears to be best adapted to develop in the autumn period, when its larval food (i.e., olive fruit) is at optimal condition for larval growth. Sexual maturation of females is delayed by high temperatures in summer.
Larvae of the spring and summer generations mainly pupate in the fruits. In autumn, larvae actively leave the fruits and drop to the soil for pupation.
The typical population fluctuation during the year is as follows: In spring, flies emerge from overwintering pupae in the soil and lay eggs into olives. There are 1-3 generations pupating mainly in the fruits in spring. When the weather becomes hotter in summer, newly hatched flies do not become sexually mature. They “hang around” as adults until autumn when temperatures decrease. Then they reach sexually maturation and start to lay eggs to produce another 1-2 generations. Contrary to the spring generations, most of the larvae of the autumn generations drop to the ground to pupate and to overwinter as pupae.
The larvae (maggots) of the olive fruit fly feed inside the fruit, destroying the pulp and allowing the entry of secondary bacteria and fungi that lead to rotting of the fruit. Feeding damage can cause premature fruit drop and reduce fruit quality for both table olive and olive oil production.