Genetic maps of the sheep blowfly Lucilia cuprina: linkage-group correlations with other dipteran genera.

Linkage data and revised genetic maps for 72 autosomal loci in Lucilia cuprina are presented. Comparison of the linkage relationships of biochemically and morphologically similar mutations in Ceratitis capitata, Drosophila melanogaster, and Musca domestica supports the hypothesis that the major linkage elements have survived relatively intact during evolution of the higher Diptera. The relationship of the linkage groups of the mosquito Aedes aegypti to these species is less clear.

Male crossing over and genetic sexing systems in the Australian sheep blowfly Lucilia cuprina.

Field-female killing (FK) systems based on deleterious mutations and Y-autosome translocations are being evaluated for genetic control of the Australian sheep blowfly, Lucilia cuprina. Experience during field trials has shown that mass-reared colonies of FK strains are subject to genetic deterioration, caused mainly by genetic recombination in males. A previous study found higher male recombination frequencies in two Y-linked translocation strains than in chromosomally normal males. However, the results of the present study indicate that breakage of the Y chromosome is neither sufficient nor necessary for increased levels of male recombination. The frequency of male recombination appears to be unrelated to the presence of specific chromosome rearrangements.

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.

Simulation of genetic control. Homozygous-viable pericentric inversions in field-female killing systems.

The GENCON simulation program GC5 is designed to simulate genetic population control using field-female killing (FK) systems carying pericentric inversions in addition to Y-linked translocations and deleterious mutations. Homozygous-viable pericentric inversions are included on the same chromosomes as the deleterious mutations, in repulsion to the Y-linked translocation. Released males transmit the inversions and mutations to their daughters and the translocation to their sons. Daughters are semisterile regardless of the type of male they mate with, because products of crossing-over within the inversions carry inviable duplications and deficiencies. Compared to present FK systems, inversion-containing strains give higher levels of genetic death, with both faster initial suppression and greater persistence of genetic death from field-reared descendants if releases are interrupted. At low release rates, both types of FK system are more effective than sterile males.

Homozygous-viable pericentric inversions for genetic control of Lucilia Cuprina.

The isolation of homozygous-viable pericentric inversions for inclusion in field-female killing (FK) systems in Lucilia cuprina is described. From 7,236 irradiated chromosomes screened, 16 pericentric inversions were isolated. Four of these were viable as homozygotes. One of these, In (3LR) 14, possesses the properties required for inclusion in FK systems (tight linkage of one inversion break-point to the white-eye gene and substantial genetic exchange within the inversion in heterozygous females).

Chromosomal inversions and genetic control revisited: the use of inversions in sexing systems for higher Diptera.

Genetic sexing systems based on sex-linked translocations and deleterious mutations are subject to breakdown from genetic recombination in males. Including inversions in these strains may provide a solution to this problem, by ensuring selective elimination of recombinant products. Inversions could be used either in coupling to or in repulsion to the translocation. The latter system, requiring homozygous-viable inversions, would be more difficult to construct, but would offer several advantages not available with coupled translocation/inversion systems. A system proposed for the blowfly Lucilia cuprina is outlined, which combines homozygous-viable pericentric inversions in repulsion to existing sex-linked translocations. This system should both stabilize the genetic sexing system and increase the suppressive potential of such strains.

Computer simulation of genetic control. Comparison of sterile males and field-female killing systems.

A computer program, GENCON, designed to simulate genetic control using field-female killing systems, is described. These systems incorporate sex-linked translocations and conditional lethal mutations. Genetic death in field populations is caused by semisterility of the translocation and by homozygosis of the mutations in females and non-translocation males of field origin. Simulations using the program compare the effectiveness, in populations regulated by density, of genetic control using this type of system with control using sterile-male release. At high release rates, sterile males cause more rapid suppression and earlier eradication than sex-linked translocation strains. However, if releases are interrupted before eradication, the rate of recovery of density-dependent populations is more rapid following sterile-male release than following suppression with translocation strains. In such populations, the cumulative population suppression (number of individuals killed) is greater with translocation-strain release than with sterile-male release. At low release rates, sex-linked translocation strains can be much more effective at suppressing and eradicating density-dependent populations than sterile males. In continental Australia, eradication of the sheep blowfly Lucilia cuprina is probably not practicable. A suppression campaign using sex-linked translocation strains could yield a higher benefit to cost ratio than one using sterile males.

Ecological analysis of field trials conducted to assess the potential of sex-linked translocation strains for genetic control of the Australian sheep blowfly, Lucilia cuprina (Wiedemann).

Field trials were conducted with translocation/eye colour (TE) strains of L. cuprina to measure the mating ability of the males under field conditions and assess their potential for suppressing sheep blowfly populations. Rates of increase in L. cuprina were highest in spring (3.9-9.1 per generation), consistently low during summer (0.1-0.6 per generation) and somewhat higher during autumn (1.1-3.4 per generation). The TE strains released had the potential to prevent population increases of this magnitude. Their failure to do so during these trials resulted from their low mating competitiveness (0.33) relative to that of field-reared males (1.0), inadequacy of the larval release method and the limited capacity of the experimental mass-rearing facility.

Genetic analysis of field trials of sex-linked translocation strains for genetic control of the Australian sheep blowfly Lucilia cuprina (Wiedemann).

The results of progeny tests of males and females captured during two field trials of sex-linked translocation strains for genetic control of L. cuprina are presented. Males released as mature larvae survived to adulthood and mated with field females. However, the levels of genetic death introduced into the population were insufficient to suppress the native population. This was due partly to seasonal ineffectiveness of the release method, and partly to poor performance of the released males. On average, the mating competitiveness of the released males was only one-third that of field males, whereas their field-reared, translocation-bearing sons were fully competitive with native males.

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.

Viability and fertility of sex-linked autosomal duplications in Lucilia cuprina (wiedemann).

Viable and fertile Y-linked duplications have been recovered in Lucilia cuprina for autosomal segments ranging in size from 2-12% of the autosomal polytene chromosome complement. No viable deficiency in this size range was recovered. Survival to adulthood of the duplications decreased with increasing duplication size. Genetic background also influenced recovery of some duplications. Recovery of duplications from fertile duplication-male parents was frequently much higher than from translocation-male parents, possibly due to low adjacent-1 segregation in some translocations or to meiotic-drive-type events. Chromosome 4R may contain a triplo-lethal locus. The use of sex-linked duplications in female-killing systems for genetic control programs may have considerable advantages over reciprocal sex-linked translocations, both in terms of fertility and strain stability.

The use of bridging systems to increase genetic variability in compound chromosome strains for genetic control of Lucilia cuprina (Wiedemann).

Genetic variability in the non-compound portion of the genomes of compound-chromosome (CC) strains intended for genetic control can be increased by the use of bridging strains which can be crossed to both CC and normal strains. Two bridging systems are described for chromosome-5 CC strains of Lucilia cuprina. The first system relies on the established viability and fertility of males trisomic for chromosome 5R. Males carrying the (5L.YL)23 half-translocation, a C(5R), and a normal chromosome 5 were crossed successfully to a CC strain and a normal strain. The second system uses a pair of reciprocal whole-arm 4;5 translocations to generate gametes disomic for 5R and nullosomic for 5L, which in combination with C(5L)-bearing gametes form viable near-euploid offspring with only small duplications and deficiencies. These offspring (C(5L); (4L.5R)357; (4R.5R)194; (4L.4R)) were crossed successfully with both CC and T(4;5)357/ + individuals. The latter were in turn crossed successfully with normal strains. The T(Y;5)23 system allows replacement of the non-CC genome with wild material more rapidly than the T(4;5)357/T(4;5)194 system, but unlike the latter does not allow replacement of the Y chromosome in the CC strain. The double translocation system is currently being used in L. cuprina.

Genetic instability in mass-rearing colonies of a sex-linked translocation strain of Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) during a field trial of genetic control.

Genetic breakdown occurred in a strain of Lucilia cuprina constructed for the purpose of genetic control of this pest. The strain incorporated autosomal recessive eye colour mutations linked in repulsion with a translocation involving the Y chromosome (male-determining) and two autosomes. In the original strain females had white eyes and males were wild type. The spontaneous breakdown involved a failure of the sex-limited inheritance of the eye colour mutations. Characteristically the frequency of white-eyed males increased rapidly in the strain, whereas the frequencies of the three other phenotypically recognizable breakdown products did not. This suggested that the white-eyed males had a selective advantage over both the wild type males and the other breakdown products. Genetic analysis revealed that recombination, which is normally rare in L. cuprina males, is considerably more frequent in the presence of a Y-autosome translocation, but that recombination alone was insufficient to account for the rate of increase of the white-eyed males in the colony. Genetic and cytological analysis of the breakdown products revealed that reversion of the multi-break translocation also occurred, and that many of the white-eyed males had either only a Y-single-autosome translocation or no translocation at all; thus these males were more fertile than the wild type multi-translocation males. In addition, under colony cage conditions the white-eyed males may have had a behavioural advantage in competition with the wild type males.

The synthesis of compound autosomes in the Australian sheep blowfly Lucilia cuprina.

The synthesis of the first compound chromosome strain in Lucilla cuprina (Diptera: Calliphoridae) (Weidemann) is described. Crosses between the compound chromosome strain and a chromosomally normal strain produce no offspring, whereas crosses between compound chromosome-bearing individuals are fertile. Cytological evidence is presented that compound chromosome arms assort art random with respect to one another during spermatogenesis.

Genetics of lucilin, a storage protein from the sheep blowfly, Lucilia cuprina (Calliphoridae).

Lucilin, the main storage protein of larval fat body and hemolymph in the sheep blowfly, Lucilia cuprina, has been isolated as a series of trimers composed of subunits of 83,000 +/- 5%, daltons. Extensive electrophoretically detectable polymorphism of lucilin subunit patterns occurs in wild and laboratory populations of Lucilia; from four to nine bands are seen in any one individual. Evidence from genetic, electrophoretic, immunological, and structural studies suggests the existence of a series of 12 or more closely related structural loci (designated Luc-1 to Luc-12) which may have arisen through gene duplication. Codominant allelic variation has been found at several of these loci. Luc-1 and Luc-3, and probably the other structural loci of the series, are located on chromosome 2.

Negative complementation at the notch locus of Drosophila melanogaster.

Four Abruptex alleles (AxE1, AxE2, Ax9B2, and Ax16172) have been mapped within the Notch locus. Based on their visible phenotypes and their interactions with one another and with N mutations, the Ax alleles can be divided into two groups. Heterozygous combinations of members of the same group are intermediate in phenotype compared to the respective homozygotes, whereas heterozygotes of Ax alleles from different groups exhibit negative heterosis, being much less viable and more extremely mutant than either homozygote. It is suggested that the Notch locus is a multi-functional regulator ("integrator") gene, whose product possesses both "repressor" and "activator" functions for the processes it regulates.