HAWAIIAN PICTURE-WING FLIES } Drosophila spp.
HABITAT: Hawaiian picture-wings can be found in most natural communities in Hawaii and have adapted to a diversity of ecosystems ranging from desert-like habitats to rainforests and swampland. The larvae of each picture-wing species are dependent upon only a single or a few related species of plants.
RANGE: Each species of Hawaiian picture-wing fly is found only on a single Hawaiian island; listed picture-wings inhabit the islands of Oahu, Molokai, Hawaii, Kauai, and Maui.
MIGRATION: Picture-wings do not migrate seasonally.
BREEDING: Breeding generally occurs year-round, but egg laying and larval development increase following the rainy season. Males occupy territories that serve as mating arenas and attract receptive females. The males of different species use different techniques to ward off competing suitors. When a male has secured his position, he performs a detailed choreography of behaviors for females, with each species having its own ritual. If he does not convey the right moves and messages, she leaves without mating. After mating, females lay between 50 and 200 eggs in a single clutch.
LIFE CYCLE: After larvae hatch, they molt through three successive stages before changing into pupae. Within a month they metamorphose and emerge as adults. Adults generally become sexually mature one month later and live for only one to two months.
FEEDING: Adult flies feed on decaying matter. The larval stages of most species are saprophytic (feeding on decaying vegetation, such as rotting leaves, bark, flowers, and fruits). Some picture-wing species have become highly specialized; for example, some feed carnivorously on egg masses of spiders, while other feed on aquatic green algae.
THREATS: Hawaiian picture-wings have declined because of habitat destruction and the loss of their host plants. Remaining species are threatened by degradation of their habitat due to feral animals and invasive plants, loss of host plants, predation by introduced yellow jackets and ants, cattle grazing, and fire.
POPULATION TREND: Surveys from 1965 to 1999 showed declines of all the listed picture-wing species. For example, the hammerhead picture-wing (D. heteroneura) formerly occurred at 16 sites on four of the island of Hawaii’s five volcanoes. It disappeared from every site and was feared extinct until rediscovered at a single site on the Hualalai volcano in 1993.