Most isopods reproduce sexually and have two separate sexes. However, there are some species known to be hermaphroditic and even some that can reproduce via parthenogenesis. Parthenogenesis is a form of asexual reproduction in which an egg does not need to be fertilized to produce a viable embryo. This means even a single isopod kept alone can still produce viable offspring. The dwarf white isopod, Trichorhina tomentosa, is an example of a commonly kept isopod species that can exhibit this trait. 

For the most part, though, you will need a culture with both males and females present in order to have offspring. As a form of courtship, males will engage in a practice called "mate guarding." When a male finds a potential mate, he will grab onto the female's back and ride on top of her until she's ready for or receptive to mating. If the male successfully fertilizes a female, she will then produce a clutch of eggs known as a "brood."

The brood will be kept in a special pouch called the marsupium on the underside of the female until they are fully developed. The female will then release the baby isopods, called mancae, from the marsupium and will protect the babies for several days. The length of time spent protecting their offspring will vary by species. Mancae will look almost like tiny adults, and can even roll into protective balls (if this is a trait the species has as adults). As they grow, they will molt their exoskeleton several times. The growth rate, reproductive size, and reproductive age will vary by species.

The size and frequency of broods will depend on species, environmental factors, and food availability. Some species will produce larger broods or reproduce more frequently if they have access to additional protein sources. Some species will reproduce consistently through the year, and some will only reproduce at certain temperatures. Others may only produce one or two broods in a year, like some Cubaris species, and others may only produce a single brood in a lifetime, like Helleria brevicornis. You will have to research the traits of your specific species and adjust the care as needed.