We suggest a new phylogenetic hypothesis for the tripunctata radiation based on sequences of mitochondrial genes. Phylogenetic trees were reconstructed by parsimony, maximum likelihood and Bayesian methods. We performed tests for hypotheses of monophyly for taxonomic groups and other specific hypotheses. Results reject the monophyly for the tripunctata group whereas monophyly is not rejected for the tripunctata radiation and other specific groups within the radiation. Although most of the basal nodes were unresolved we were able to identify four clusters within the tripunctata radiation. These results suggest the collection of additional data before a proper taxonomic revision could be proposed.

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The presence of three dark spots on the abdomen is typical of the tripunctata group of Drosophila, which is the second largest Neotropical group, with 56 species. In some species, such as D. mediopunctata, the colour pattern varies considerably: ranging from flies showing no spots up to flies with three dark spots. In this paper, we present a genetic (chromosomal) analysis of this character showing that this colour polymorphism is genetically determined mainly by the second chromosome. Since this chromosome is the most polymorphic for inversions in this species, we also examined the influence of the inversions on this character. We used strains in which different second chromosomes were placed on the same genetic background and the offspring between them. We found a nonrandom association between the number of spots and the inversions PA0 and PC0. Thus, our results are consistent with the idea that the factors or genes determining a conspicuous polymorphism are likely to be associated, forming a supergene, and this association would be most efficiently accomplished through a chromosome inversion. Moreover, this is the first time that an association between a conspicuous morphological polymorphism and chromosome inversions has been described.

Cochliomyia hominivorax and Cochliomyia macellaria are endemic Neotropical Calliphoridae species. The former causes severe myiasis in hosts while the latter is Sarcosaprophagous, but commonly found as a second invader in wounds. Due to the morphological similarity between them and the potential losses that C. hominivorax represents for cattle breeders, the rapid and correct identification of these two species is very important. In addition to a correct identification of these species, a good knowledge of C. hominivorax biology can be helpful for designing control programs. We applied geometric morphometric methods to assess wing differences between C. hominivorax and C. macellaria and conduct a preliminary analysis of wing morphological variation in C. hominivorax populations. Canonical variate analysis, using wing shape data, correctly classified 100% of the individuals analyzed according to sex and species. This result demonstrates that wing morphometry is a simple and reliable method for identifying C. hominivorax and C. macellaria samples and can be used to monitor C. hominivorax. Both species show sexual dimorphism, but in C. hominivorax it is magnified. We suggest that this may reflect different histories of selection pressures operating on males and females. Significant differences in wing size and shape were obtained among C. hominivorax populations, with little correlation with latitude. This result suggests that wing variation is also a good morphological marker for studying population variation in C. hominivorax.

An excess of females in progenies is commonly referred to as sex-ratio (SR). In this report, we describe three new occurrences of SR in species of the tripunctata radiation, Drosophila neocardini, Drosophila ornatifrons and Drosophila paraguayensis. Repeated backcrosses with males from normal strains were used to maintain the SR strains in the laboratory, always with all-female broods. The egg-larva viability of the SR strains was approximately half that of a normal strain, and antibiotic treatment restored the production of males in SR strains. PCR screening with Spiroplasma-specific primers showed that only SR strains tested positive for Spiroplasma. The results showed that in the three species, SR was maternally inherited and involved early male-killing bacteria, most likely spiroplasmas. These new occurrences increase the number of cytoplasmic male killers described in Drosophila from 11 to 14. In this particular collection of flies, one quarter (3 out of 12) of the species from the tripunctata radiation of Drosophila was infected with a male killer, suggesting that this group may be a hot spot for the presence of male-killing organisms.