The modern cockroaches do have an ovipositor which is either a very short or internal ovipositor, which is also different from the cockroaches ancient ancestors, which had long external ovipositors.
The internal ovipositors in modern cockroaches are used to deposit the egg case, or ootheca, which the female then carries before they leave it in a safe place to hatch.
Ancient cockroaches also called roachoids, had long, external ovipositors for laying of eggs directly into a substrate.
But modern cockroaches have evolved a much reduced, internal ovipositor.
The internal ovipositor in modern cockroaches is used by the female cockroach to produce and lay the egg case called the ootheca.
The difference between a stinger and an ovipositor is that a stinger is a modified ovipositor, and both are sharp, tubular organs that are found in female insects and the primary functions of a stinger and an ovipositor differ.
An ovipositors main function is to lay eggs, either on or into a substrate like a host insect or plant.
A stinger is a weapon for use as defense, which is created through the evolution to inject venom, although some insects that have ovipositors use their modified ovipositors for both injecting venom and laying eggs.
Ovipositors are not only for eggs although egg laying is the primary function of ovipositors.
Ovipositors can also be modified for other functions and most notably to be used as stingers or for paralyzing prey.
The ovipositors are a versatile organ that has functions that depends on the species that has the ovipositors, which can use the ovipositors to drill into plant tissue, wood or even the host insect to deposit the eggs.
Sawflies use a modified, saw like ovipositor to allow them to slit the tissues of plants to lay their eggs in.
And some wasps use their ovipositors to inject eggs and often a paralyzing agent into another host animal, like a caterpillar.
Grasshoppers use their ovipositors to burrow into the earth, and cicadas use their ovipositors to pierce twigs to lay eggs.
And in many social bees, ants and wasps, the ovipositors have been modified into a stinger for use as defense.
And some ovipositors also have sensory organs that help the insect with the ovipositors in determining the best location to lay their eggs.
And in some species of insects, the ovipositors is also used in gathering of a spermatophore during mating.
The ovipositor is a tube like organ that is used by some animals and especially insects, for the laying of eggs.
Not all insects have ovipositors, but most female insects do possess an ovipositor, but it's absent in some species, including certain termites, parasitic lice, and many mayflies and stoneflies.
Ovipositors are tube like organs which are mainly used for laying eggs but some insects like bees and wasps have modified ovipositors that they use as a stinger.