How lethal are homozygous balancers?

[Pasha]

Hi,
The question above will no doubt sound a little odd, but I'll explain.
I did some cuticle preps to look at the penetrance of a loss-of-gene-function cuticle phenotype. Although this penetrance was extremely low, I got a much higher penetrance of cuticle phenotypes showing abdominal denticles 1, 2 and 7 partially missing or missing completely. The strains I am looking at are balanced, and I wonder whether these phenotypes are attributible to embryos/L1s that are homozygous for the balancers (e.g. CyO/CyO).
Does anybody know of any literature on homozygous lethal balancers, at which stage of development lethality takes place and if cuticle phenotypes have been observed for homozygous individuals?
Thanks.