Npc1a^unspecified males in which lethality has been rescued by expression of Npc1a^{Scer\UAS.T:Avic\GFP-EYFP} under the control of Scer\GAL4^2-286 are sterile. The seminal vesicles of the mutant males are much smaller than wild type and contain essentially no mature sperm, but an accumulation of sperm debris is seen in the basal region of the testis. A mild cytokinesis defect (penetrance 5.79%) is seen, but the mutants have a similar number of spermatids per cyst as wild type at the elongated stage. The individualisation complex assembles normally at the head region of the spermatid bundle in the mutant males. However, it gradually disintegrates as it moves along the cyst and scattered actin cones are seen. Some sperm nuclei are scattered along the cyst in the mutant males (in wild-type males they are clustered at the head of the cyst) and these scattered sperm nuclei lose their needle-like shape, becoming more condensed and rounded the further away from the head region they are. 28 +/- 16% of mutant spermatids show defects in individualisation and the average number of spermatids per cyst after individualisation is reduced to 54. Mutant spermatocytes show sterol accumulation and sterol trafficking defects. Individualisation defects are more severe at higher temperatures.

The fertility of Npc1a^unspecified males in which lethality has been rescued by expression of Npc1a^{Scer\UAS.T:Avic\GFP-EYFP} under the control of Scer\GAL4^2-286 is significantly increased by addition of 7-dehydrocholesterol in the food, but is not increased by the addition of cholesterol, ergosterol or sitosterol in the food.