Larval selectivity for yeast species by Drosophila mojavensis in natural substrates.

The yeast flora found in the major substrates of Drosophila mojavensis and in larval guts was studied both qualitatively and quantitatively. Quantitative studies show that, in four of the five substrates tested, the larvae did not contain a random sample of the yeasts present in the substrates. One widely distributed cactus yeast, Pichia cactophila, was typically in greater frequency in the larvae than in the substrates. Another cactus yeast, Candida sonorensis, typically exhibited the opposite relationship. Laboratory tests support larval preference behavior rather than differential digestion as being primarily responsible. Larvae are capable of distinguishing between patches of different yeast species and spend more time in patches of preferred yeasts. D. mojavensis appear to be ecological (host plants) generalists and physiological (yeasts) specialists in contrast to the other cactophilic Drosophila. Selective feeding by D. mojavensis larvae in natural substrates may represent optimal foraging behavior.