Induction of suppressed ADH activity in Drosophila pachea exposed to different alcohols

Laboratory-reared males of the cactophilic Drosophila pachea exhibit a spontaneous and sex-specific suppression of alcohol dehydrogenase (ADH) activity within 4 days after eclosion. A lack of ADH activity also is usually seen in wild-caught males, although relatively high activity is always seen in female flies. In the present study we examined the effectiveness of different alcohols and related compounds, including several found naturally in necroses of the host cactus, to induce suppressed ADH activity in wild males of D. pachea and to serve as enzyme substrates. The primary alcohols (methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol), and the secondary alcohols (2-propanol and 2-butanol), each induced activity after 24 h exposure, although to different degrees. 1,2-Propanediol was usually effective as an inducer, but 2,3-butanediol usually was ineffective. Little or no induction was seen with 1-octanol, 2-pentanol, 3-methyl-1-butanol, 3-hydroxy-2-butanone, or acetaldehyde. Although the compounds tested varied in their ability to function as ADH substrates, methanol was the only alcohol that showed no activity staining. Ethanol induction of ADH activity was apparent after 3-6 h exposure and induced activity decreased dramatically within 1 week of flies being placed in an alcohol-free environment. Ethanol exposure did not induce ADH in adult female D. pachea, or in adult males and females of D. acutilabella in which control males show reduced ADH activity compared to females. The implications of the loss of ADH activity in adult males of D. pachea, as they relate to feeding ecology and fitness, are discussed.