The introduction of exotic plants creates potential new niches for endemic animals. European tradespeople brought the cactus Opuntia ficus-indica in the 16th century from Mexico to Europe to serve as substrate for the cochineal insect (Dactylopius coccus), which is used for the production of red dye. Cosmopolitan frugivorous Drosophila species as D. melanogaster, D. simulans, and D. hydei are known to use the fruits of this exotic plant (Carson, 1965; Haouas et al., 1984, Santos et al., 1999). Whereas the cactophilic species Drosophila buzzatii is not known to breed outside its plant-specific niche, i.e. decaying cladodes and cactus fruits (Carson, 1965), we show that D. simulans made a start to adapt to the non-fruit part of 0. ficus-indica. (A) Naturally rotting 0. ficus-indica pads were collected in a semi-abandoned 0. ficus-indica plantation in southern Spain, 3 km north of Carboneras (37 OI'N, I 52'W) (Eisses and Santos, 1997).
However, in rotting cladodes, larvae can survive only if they can tolerate the slow release of nutrients the decay of cactus material provides, which is one of the adaptations made by cactophilic Drosophila species. D. simulans from the Carboneras area showed a broad range of development times in fresh and rotting cladode patches. Comparative experiments with D. simulans strains from geographically separate areas would show whether these results apply only to adaptation'> of a local race of D. simulans or to D. simulans in general. The fact that D. simulans can develop into viable adults utilizing the resources in cladodes probably allows it to persist in the area between the successive fruiting seasons. Flies were trapped in the Carboneras area in April 1995, when no prickly pears were present: D. simulans was present in similar numbers to D. buzzatii. The beginning of a niche expansion by D. simulans may have been witnessed in the arid area of Carboneras.