Genetic sexing in the mediterranean fruit fly, Ceratitis capitata, using the alcohol dehydrogenase locus

Using the alcohol dehydrogenase (ADH) locus a genetic sexing system is being developed in the Mediterranean fruit fly Ceratitis capitata based on the sensitivity of ADH null mutations to environmental ethanol. A series of null mutants have been induced at this locus, however, none proved viable as homozygotes. One of these null mutants was translocated to the male determining chromosome and this line can be used for genetic sexing. When larvae from this line were reared on larval medium containing various concentrations of allyl alcohol, 97% of the emerging adults were males; in the absence of the allyl alcohol the sex ratio in the line is distorted in favour of the females. It is proposed that the higher ADH activity of the females (homozygous positive) in comparison with the males (heterozygous null) is responsible for their lower survival in larval medium containing allyl alcohol. ADH converts the allyl alcohol to the lethal ketone. The possible use of this line to sex large populations of medflies for use in sterile insect release programmes is discussed.