Living With Insect Eggs

Squash bug eggs. Eggs are white when first laid, but turn brown due to sclerotization (cross-linking of proteins).

The eggs of insects consist of a nutrient yolk surrounded by a proteinaceous outer layer. In many insects, the eggs, when first laid, are soft and white or colorless. Over time the eggs harden and darken, often to a brown color. The color change is due to sclerotization, the cross-linking of the proteins in the outer layer of the egg by reactive chemicals. The sclerotization shields the eggs somewhat from potential predators and pathogens. However, hardening is not the only protection. The reactive chemicals responsible for the sclerotization can also react with the proteins of pathogens to inhibit or kill a pathogen. This raises an interesting question for physiologists. Is the egg hardening necessary for protection of the embryo and proper development? Or is the hardening a by-product of the reactive chemicals that protect the egg from pathogens?