Drosophila buzzatii and D.koepferae are sibling cactophilic species.The former breeds primarily on prickly pears (genus Opuntia) whereas the latter breeds on columnar cacti of the genera Cereus and Trichocereus,although with certain degree of niche overlapping.We examined the interspecific differences in dial temporal patts of adult emergence from puparia and evaluated whether this behavior is affected by rearing in the different cactus hosts available in nature.We detected important host-dependent genetic variation for this trait differentially affecting the emergence schedule of these species.Dial patt of emergence time was directly correlated with developmental time and negatively correlated with adult wing size,suggesting that early emergences are at least indirectly correlated with increased fitness.We discussed our results in terms of their putative effects on fitness and the genetic-metabolic pathways that would be presumably affected by host’s nutritional-chemical differences.