Collateral Glands

The collateral glands of insects are organs linked to the female genital apparatus. Collateral glands are two extremely branched tubular glands in cockroaches, which are uneven in size. Both the glands open at the back of the genital chamber. The secretion generated by these glands forms the oothecal case of the ootheca.

It consists of standard proteins and some substances that cause hardness all over the eggs, which provide protection and stability. Its appearance is dark reddish-brown in colour. Its shape is upright. 

Functions of Colleterial glands

The collateral glands are found in the third and fourth abdominal sections of the female cockroach. The secretion from the collateral glands forms the oothecal case. The water balance is maintained by ootheca through the difference in the surface i.e., in the dry climate to protect against over-saturation. The protein may not be directly related to the development of ootheca although the latter possibly secretes resistance within the outer layer of the ootheca.

Scientific Classification

The collateral gland of insects is primarily an organ linked to the female genital apparatus. A cockroach is from the kingdom of Animalia, its subphylum is Hexapoda, its phylum is Arthropoda, its order is Blattodea, its superorder is Dictyoptera, and its class is Insecta.

Cockroaches are dioecious in nature, i.e., they contain separate female and male sexes. A cockroach is also known as a roach. The cockroach chooses a warm, wet, gloomy environment and usually lives in tropical or other moderate temperatures. Both female and male cockroaches have external genitalia. 

The male external genitalia contains three phallomeres or male gonapophyses. They encircle the male gonopore at the end of the abdomen. An ovipositor is present in the female external genitalia, which is formed by two gonapophyses. They remain concealed in the gynatrium. The ovipositor is used to conduct fertilised eggs to the oothecal chamber. 

The internal male reproductive system of cockroaches is made up of the conglobate gland, utricular gland, ejaculatory duct, vasa deferentia, and a pair of testes. The internal female reproductive system has a couple of ovaries, spermatheca, collateral glands, a genital pouch, and a vagina. Glands unique to female cockroaches are the collateral glands. The pair of glands join and then open into the dorsal side of the genital chamber.

The collateral glands are tubular glands in cockroaches, which are not the same in size. Both glands are not closed on the back, in the genital chamber. Secretion generated by these glands forms the oothecal case of the ootheca.

The female cockroach contains two collateral glands that form a hard egg case all over the egg, known as an ootheca. The ootheca is composed of protein structures that cause the protein to get harder around the eggs, in order to protect them.

The collateral glands of the cockroach are the sexual accessory glands that generate the brown, strong, flexible material of the egg capsule. There are two glands, a right and a left, and each are composed of a mass of branched tubules. The two vary in size, features, and appearance. 

The left gland, which is much bigger, generates an opaque, white, bulky secretion consisting primarily of the structural protein, which later constitutes the largest part of the egg capsule, and a glucoside of aromatics participating in the further hardening of the protein. The secretion also reveals the powerful phenoloxidase activity. The right gland is known to secrete a β-glucosidase.

Cockroach Gestation

This section covers reproduction in different types of cockroaches:

• American cockroach
  These cockroaches lay eggs in a case, which is termed an ootheca. Approximately a week after the mating period, an ootheca is produced by a female. On average, a single ootheca is produced by females every month for a period of ten months, which lays around 16 eggs per case.

• German cockroach
  This type of cockroach generates more eggs per ootheca compared to other cockroaches. The German cockroach can carry 30 to 40 every time. Female German cockroaches hold the ootheca on their body, until the eggs are ready to hatch. 28 days is the gestation period (on average) for a German cockroach.
• Brown-banded cockroach
  In brown-banded cockroaches, around 16 eggs per ootheca can be carried. The ootheca is held by a female cockroach for nearly a day or two. The egg case is then stuck to cardboard, wall, furniture, or another surface that is rough. Within approximately 50 days, the eggs will begin to hatch.
• Oriental cockroach
  Oriental cockroaches hold an average of 16 eggs per ootheca. The female of this type of cockroach drops the egg cases in areas that are warm and protected, and where food is easily available. The period of incubation lasts approximately two months.

Conclusion

In cockroaches, during oviposition, collateral glands generate secretions that cover two parallel rows of eggs. In oviparous species, these secretions turn into the sculpted, tanned, and rigid outer casing of the ootheca.