Medflies undergo a complete metamorphosis, beginning life as larvae and transforming into completely different-looking adult fruit flies. Females lay their eggs approximately 1 mm beneath the skin of host fruit. Although each female lays only 2 to 10 eggs in a given fruit, multiple females may lay their eggs in the same location, so that the slim, smooth, white eggs, about 0.1 cm long, may be clustered together in a single spot of seventy-five or more.
After 1.5 to 3 days (longer if the temperature is lower) the eggs hatch. The larvae carve tunnels, eating their way through the fruit. Larval life may last a mere 6 to 10 days (when temperature is around 25ºC). Along with temperature, the type of host fruit affects the length of the larval stage. In citrus fruits, 14 to 26 days may be required to reach pupation. Development in a green peach is completed in 10 to 15 days.
There are three larval stages, or instars. In the first, larvae are slender, cream colored, translucent, and about 0.1 cm long. In the second instar, larvae are partly transparent, revealing the fruit in the gut. By the third instar, larvae are opaque white and 0.6 to 0.8 cm long. These larvae can be distinguished from other fruit fly larvae by their thoracic spiracles, with 7 to 11 small protruding tubules.
Most larvae begin to pupate at sunrise, an inch or two into the soil. The pupal stage lasts from 6 to 13 days at around 24.4ºC. This range significantly increases (possibly to about 19 days) when the temperature drops to around 20.5ºC. The pupal stage is resistant to temperature extremes and dessication, so it may last much longer if conditions are not right for emergence. It is typical for the new adult medflies to surface on warm mornings. At this early adult stage, they are capable of flying short distances, and may disperse further distances via the wind.
Development - Life Cycle: metamorphosis