The use of sterile males to control populations of Queensland fruit fly Dracus tryoni (Frogg) (Diptera : Tephritidae) II. Field experiments in New South Wales

Abstract

In the field trials of sterile males against the Queensland fruit fly, Dacus tryoni, irradiated pupae of this species were distributed in three towns of western New South Wales in the period September 1962 to March 1965. All these towns and a number of others which served as controls had a previous history of heavy infestation by Dacus tryoni. The success of this method was estimated by comparing the rate of infestation of ripe fruit in treated and untreated towns. The first sign of success came in Manilla in spring (October) 1963 when 51.0% of the eggs deposited in loquats were estimated to be infertile compared with 6.7% in three control towns. However, our production of pupae at this stage was too low to maintain control in Manilla in the summers of 1962-63 and 1963-64. From late April 1963 to late March 1964 most of our production was released in the town of Warren. With a total release in this period of 5.7 x 106 pupae we achieved infestation rates of 2-8% in the summer fruit between early December 1963 and late March 1964, compared with infestation rates of 8-75% in three control towns during the same period. Towards the end of March 1964 the infestation rates began to rise in Warren apparently owing to the immigration of inseminated females along the Macquarie River. An infestation rate of 20% was reached in Warren in April 1964. Between early December 1964 and late March 1965 the rates of infestation in Warren were even more depressed, reaching values of 0 - 7.5% compared with 10-57% in the new control town of Baradine. The total number of pupae released within the town between August 1964 and March 1965 was 12.57 x l06. However, immigrants again brought the infestation up to 10% in April 1965 even though an additional 2.67 x l06 pupae had been distributed along the river for 6 km on either side of the town. In the same period (summer 1964-65) Dacus tryoni was eradicated from Trangie where its numbers had been brought down by trapping out the males with a male lure (Bateman 1966). No infestation was found from October 1964 to April 1965 after the release of 5.33 x l06 pupae between late August 1964 and late March 1965. The rate of infestation in the control town of Gilgandra which had also been treated with cue-lure in the previous summer rose from 0% on October 21, 1964 to 16.2% by April 23,1965. The method could be used to suppress incipient outbreaks of Dacus tryoni in southeastern Australia and even for the eradication of established populations where these are isolated and can be brought low by other means.