Further development of a low-cost release method for sterile Queensland fruit fly Bactrocera tryoni (Froggatt) in rural New South Wales

Abstract

Sterile Queensland fruit fly (QFF) Bactrocera tryoni (Froggatt) were released using a pupal-release technique in part of Wagga Wagga. Between August 1997 and May 1998, sterile flies were released using initially sand and later vermiculite mediums in the bed technique. A total of 234.16 million pupae were delivered, with an overall emergence rate of 41.4% and male recapture rate of 0.0365% based on emerged flies. A male recapture rate of 0.0141% was calculated from the male pupae deployed, not corrected for emergence. Released sterile flies were recaptured up to 74 days after release. Of the 16 563 males recaptured, 99.3% of sterile flies were trapped within 1�km of release sites. The CLIMEX model was used to rank the climate at Wagga Wagga to better understand emergence and recapture rates during this and earlier programs. CLIMEX indicated that the 1997–98 year was hotter and drier than both the 2 previous years and the long-term average. The Meats daily survival rate decrement formula was also used to compare quality of sterile flies. Results from previous suppression programs were compared using these parameters. In winter 1998 at Junee, pupae were deployed in foam eskies where emergence varied from 0 to 29%, with CLIMEX Cold Stress at an average of 481. Emergence occurred over a 4-week period. In the 1998–99 summer at Lake Cargelligo, sterile flies were deployed using the pupal-release technique. Foam containers replaced the metal trays from the previous season to afford better insulation from the heat. The average emergence rate was 64% for the program. A male recapture rate of 0.071% was calculated from the 9.12 million pupae deployed or 0.11% from the estimated emerged males. An overflooding ratio of 3.2 was achieved for the season, with some apparent suppression of wild fly populations. The last recaptured sterile fly was trapped 77 days after the final release. CLIMEX, with and without irrigation, was used to assess the suitability of Lake Cargelligo and surrounding rural areas for QFF survival.