Differential attraction of drosophilids to banana baits inoculated withSaccharomyces cerevisiaeandHanseniaspora uvarumwithin a Neotropical forest remnant

Abstract

BackgroundYeasts are a necessary requisite in the diet of mostDrosophilaspecies that, in turn, may vector their dispersal in natural environments. Differential attractiveness experiments and the isolation of yeasts consumed byDrosophilamay be informative for characterizing this association.Hanseniaspora uvarumis among the most common yeast species isolated fromDrosophilacrops, with high attractiveness to drosophilids.Saccharomyces cerevisiaehas been widely used to collect flies, and it allows broad sampling of almost all localDrosophilaspecies. Pronounced differences in the field concerningDrosophilaattractivity to baits seeded with these yeast species have been previously reported. However, few explicit generalizations have been set. Since late fifties, no field experiments ofDrosophilaattractivity were carried out in the Neotropical region, which is facing shifts in abiotic and biotic factors. Our objective is to characterize preference behavior that mediates the interaction in the wild among NeotropicalDrosophilaspecies and yeasts associated with them. We want to set a broad generalization about drosophilids attracted to these yeasts. Here we present the results of a differential attractiveness experiment we carried out in a natural Atlantic Rainforest fragment to assess the preferences ofDrosophilaspecies groups to baits inoculated withH. uvarumandS. cerevisiae.MethodsBoth yeast species were cultured in GYMP broth and separately poured in autoclaved mashed banana that was left fermenting. In the field, we collected drosophilids over five arrays of three different baits: non-inoculated autoclaved banana and banana inoculated with each yeast. In the laboratory the drosophilids were sorted to five sets according to their external morphology and/or genitalia:tripunctata;guarani;willistoni;exotic; and the remaining flies pooled inothers.Results and ConclusionsUninoculated banana baits attracted virtually no flies. We found significant departures from random distribution over the other two baits (1:1 proportion) for all sets, except the pooledothers. Flies of the setswillistoniandexoticpreferredH.uvarumoverS.cerevisiae,while the remaining sets were more attracted toS.cerevisiae. Previously, various authors reported similar patterns in attraction experiments withS.cerevisiaeandH.uvarum. It is also noteworthy that both yeast species have been isolated from natural substrates and crops ofDrosophilaspecies. Taken together, these results suggest that the preferences amongDrosophilaspecies groups may be reflecting deep and stable relations with yeast species in natural environments. They can be summarized as: forest dwelling species from subgenusDrosophila(such astripunctataandguaranigroups) are attracted to banana baits seeded withS.cerevisiae; while exotic (asD. melanogaster) and subgenusSophophoraspecies are preferentially attracted to baits seeded withH.uvarum.