Expression of LardsRNA.Scer\UAS.THFC in 2 to 16-cell spermatogonia under the control of Scer\GAL4bam.T:Hsim\VP16 results in almost complete male sterility. The testes of the transgenic animals have defective elongating and elongated spermatids and no mature sperm. Some cysts close to the testis apex lack germ cells in animals expressing LardsRNA.Scer\UAS.THFC. As a result of transgene expression, enhanced somatic cell proliferation and differentiation, a likely compensatory effect to the loss of germ cells, is also observed.