Answer:
Cross the flies with the flies from another population
Step-by-step explanation:
Inbreeding is the mating between the closely related individuals of a population. Inbreeding reduces the viability of the progeny over a generation since it increases homozygosity. When the flies of a small population interbred over generations, the increased homozygosity reduces the viability of the flies. To counteract it, one should mate these flies with the flies from another population. This would increase heterozygosity and thereby would increase the survival and fitness of the progeny.