Population Suppression and Sterility Rates Induced by Variable Sex Ratio, Sterile Insect Releases of Ceratitis capitata (Diptera: Tephritidae) in Hawaii

Abstract

Sterile insect releases of a pupal color-based genetic sexing strain of the Mediterranean fruitfly, Ceratitis capitata (Wiedemann), were made during the summer and fall of 1991 in coffee plantations in Kauai, HI. Four treatments compared with respect to trap recapture and sterility rates induced in native populations were: (1) genetic sexing strain (≈99% males = males only), (2) genetic sexing strain (males and females), (3) genetic sexing strain (high % ♀♀), and (4) standard strain (males and females). Each week either 2 liters (≈120,000) of irradiated pupae for the bisexual populations or 1 liter of irradiated pupae for the unisexual populations were dye-marked and ground released in buckets. Adult flies emerged and dispersed throughout individual (≈1 ha) coffee fields. Flies were trapped weekly in standard dry traps or in liquid protein traps. Coffee berry samples were collected weekly to determine egg sterility rates, and females trapped in liquid protein were dissected for presence of sperm and sperm type. A new technique was developed to type sperm as either sterile (irradiated) or wild in mated females. An estimate of sterile fly competitiveness based on relative degrees of egg hatch suppression indicated an overall three- to five-fold increase in competitiveness of the males-only strain compared with the standard bisexual strain. Significantly, however, this difference even widened to a qualitative degree by the end of the test.