Field trial of a compound chromosome strain for genetic control of the sheep blowfly Lucilia cuprina.

In 1979-80 a field trial of a compound chromosome (CC) strain of the Australian sheep blowfly Lucilia cuprina was conducted in the isolated Brindabella Valley, N.S.W. New genetic material was introduced into the strain before release by inducing 104 new CC elements by irradiation of recently captured field strains, and combining the resulting strains. Weekly releases, averaging 1.1 million larvae per week, were begun in November 1979 and continued to May 1980. Field-inseminated females were trapped weekly and their genotypes and those of their mates were determined through genetic testing. The proportion of wild X wild matings declined from 16% in December 1979 to 1% in April 1980. During this period the proportion of CC X CC matings rose from 50% to 90%. Larvae sampled from infested sheep had compound chromosomes, indicating that compound chromosomebearing females can successfully oviposit in the field. Trapping of flies resumed at the start of the 1980-81 season, without further releases. Progeny tests revealed the presence of both CC and wild flies. The proportions of CC X CC matings among field-inseminated females were 90% in October, 44% in November, nil in December, and 12% in January. No CC X CC matings were detected in 33 field-inseminated females trapped and tested during April, and 70 tested males reared from myiasis samples in April 1981 proved to be wild type. These results indicate that the CC strain overwintered in the field and strongly suggest that it bred in the field for at least one generation following the spring emergence before being eliminated from the population.