Other Egg Coverings

The colleterial glands (based on colle from Greek for glue) are accessory glands of the female's reproductive system that produce egg coatings. Most simply, glue is produced to attach eggs to a substrate. In addition, some coatings deter predators or parasites chemically.

Insects in the orthopteroid orders Blattodea, Mantodea, and Orthoptera, as well as some beetle taxa, secrete an egg case or pod surrounding the eggs, to give additional protection from desiccation and predation. As with eggshells, these egg casings must be constructed to allow respiration and hatching. In cockroach eggs, the air space surrounding each embryo opens into a ventilated air duct in the keel. In grasshoppers, the colleterial gland secretions are churned into a froth in which the eggs are suspended. The entire oviposition hole is filled with the frothy material, which then hardens to form a plug. Mantids produce a similar substance from their colleterial glands, which they mold into an egg case that is attached to a flat surface or suitable vegetation.

Beetles are also known to produce egg cases, with the most complex occurring in the cassidine Chrysomelidae. Less complex ootheca have been reported in a variety of other beetle groups as well. Colleterial glands in hydrophilid beetles produce silk that is used to form a cocoon for the egg mass.

Various insect taxa use additional material to enhance protection for eggs. In some beetles, fecal material and/or secretions from anal glands apparently provide chemical defense. Some Lepidoptera use urticating (or irritating) hairs from the larval skin to protect eggs. As adult females emerge from the cocoons, they pick up discarded larval setae (hairs) with their anal tufts and later deposit them on eggs. Nonurticating adult scales, most commonly from the anal tuft, are also used by some species to create an effective physical barrier.

See Also the Following Articles

Accessory Glands • Ovarioles • Reproduction, Female

Further Reading

Hinton, H. E. (1981). "Biology of Insect Eggs," Vols. 1 and 2. Pergamon

Press, Oxford, U.K. Margaratis, L. H. (1985). Structure and physiology of eggshell. In "Comprehensive Insect Physiology, Biochemistry, and Pharmacology," Vol. 1 (Kerkut, G. A., and Gilbert, L. I., eds.), pp. 153-230. Pergamon Press, Oxford, U.K.

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