Genetic control of Lucilia cuprina: analysis of field trial data using simulation techniques.

An analytical version of the genetic control simulation program GENCON has been used to further analyze the data obtained during field trials of genetic control of the sheep blowfly, Lucilia cuprina, in 1976-79. In the simulations, population trends from a nonrelease area were used as an estimate of the rates of increase that would have occurred in the target population if there had been no releases. Genetic data from the target area (frequencies of matings by released males) were used to predict the frequencies of descendants of released males, the resulting genetic death, and the effects of this on population trends. In simulations that assumed no migration and full survival and competitiveness of all field-reared descendants of released males (translocation-bearing males and males and females heterozygous for deleterious mutations), neither the predicted genetic changes nor the predicted population trends agreed well with the observed data. Further simulations suggested that reduced survival or competitiveness of field-reared descendants did not account for this disagreement, but that immigration of wild flies into the test areas was probably a major contributor to the failure to achieve suppression. However, immigration alone was not sufficient to explain all the differences between observed and expected results. Other plausible contributors to this failure were: (1) lower survival of translocation males due to the effects of a dieldrin resistance allele carried on the translocation, and (2) increased survival of immature stages of L. cuprina at low population densities.