ALCOHOL-DEHYDROGENASE POLYMORPHISM IN BARREL CACTUS POPULATIONS OF DROSOPHILA-MOJAVENSIS

Starch gel electrophoresis revealed that the alcohol dehydrogenase (AD H-2) locus was polymorphic in two populations (from Agua Caliente, Cal ifornia and the Grand Canyon, Arizona) of cactophilic Drosophila mojav ensis that utilize barrel cactus (Ferocactus acanthodes) as a host pla nt. Electromorphs representing products of a slow (S) and a fast (F) a llele were found in adult flies. The frequency of the slow allele was 0.448 in flies from Agua Caliente and 0.659 in flies from the Grand Ca nyon. These frequencies were intermediate to those of the low (Baja Ca lifornia peninsula, Mexico) and high (Sonora, Mexico and southern Ariz ona) frequency Adh-2(s) populations of D. mojavensis that utilize diff erent species of host cacti.