Insect success can be measured in the number and survival of the progeny produced. Tiny insects have tiny abdomens and little room to devote to reproduction. A space saving arrangement in some featherwing beetles (Ptiliidae) is a reduction in the reproductive system from two to one gonads in both the male and female.
Eggs and sperm must be a minimum size to function and in tiny insects, they may be disproportionately larger in relation to the adult than in larger relatives. In tiny featherwing beetles (Bambara spp) the small eggs are so large that a female can only accommodate one mature egg at a time.* In order for the sperm to function, they are longer than the insect itself. The minimum size for viable egg and sperm may constrain further miniaturization in this group of beetles
*Dybas LK, Dybas HS. 1987. Ultrastructure of mature spermatozoa of a minute featherwing beetle from Sri Lanka (Coleoptera, Ptiliidae: Bambara). J. Morphol. 191:63–76