Roving and stationary release of adult sterile Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera; Tephritidae)

Abstract

Sterile Insect Technique (SIT) is an environmentally-benign, species-specific method of pest control. The Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is a polyphagous pest that may be managed via SIT. Sterile releases of B. tryoni were carried out in two separate field trials to compare the effectiveness of non-chilled adult (stationary release) and chilled adult (roving release) releases under field conditions in eastern Australia. The first study compared the recapture rates of sexually mature sterile male B. tryoni in cue-lure baited Lynfield traps when released as chilled adults and non-chilled adults, each on two release dates in an urban town. In a subsequent field study, trap capture rates of wild and sterile flies were monitored in three isolated towns in New South Wales that received either sterile non-chilled adult releases (Uranquinty), sterile chilled adult releases (Lockhart) or no sterile releases, i.e. control (Cootamundra). Wild fly larval counts (from whole picked fruit) were also obtained in both Uranquinty and Lockhart. In trial 1, for both release 1 and 2 respectively, a greater proportion of non-chilled flies (52.6% and 62.0%) than chilled flies (47.4% and 38.0%) were recaptured per trap. However, over the duration of the trial, recapture of chilled adult flies and non-chilled adult flies was 4.35 ± 0.54% and 3.27 ± 0.54% of all flies released, respectively. Overall, in both releases, adult flies designated for chilled adult release had lower recorded adult eclosion (except for release 2 when more chilled adults emerged) and flight compared with non-chilled adults. In trial 2, Lockhart (chilled adult release) wild fly numbers showed a significant decline four weeks after sterile release, despite both Uranquinty and Cootamundra displaying increases in wild fly numbers at this time. Chilled adults were significantly less likely to take flight than unchilled flies, but of those that dispersed, a greater proportion of the chilled flies were recaptured. Over the entire fruit collection period, there was a significant decline in the number of live larvae and the live larvae per fruit in Uranquinty and for seven consecutive weeks in Lockhart, which was also reflected in the total number of larvae and the total rate per fruit. The results are encouraging, particularly the use of chilled adult sterile release for the control of wild B. tryoni populations, and would provide a valuable tool for wild fly management.