Some Eggs of Insects That Change Color during Incubation

Abstract

When the chorion is opaque the original deposition color of the egg usually remains unchanged during incubation. Many examples of these occur among the Orthoptera, Coleoptera, Hemiptera, Homoptera and Lepidoptera, but there are some exceptions to this generalization such as the exposed overwintering eggs of many Aphididae (Homoptera) which are black or a very deep brown. At deposition time they may be cream colored, green or a light brown. For example the eggs of the apple grain aphid, Rhopalosiphum fitchii (Sanderson) and the apple aphid, Aphis pomi DeGeer, on twigs of apple trees are green when deposited, while the eggs (3)2 of Longistigma caryae (Harris) on twigs of sycamore (plane) trees are light brown. A few days to several weeks after deposition these colors change to black or near black. The pigment in these eggs is located in the tough, membranous chorion which is completely covered with a thin, transparent, adhesive coat secreted by the female when the egg is deposited. Upon exposure to air it hardens and glues the egg to the twig or leaf. It also serves as an insulation against evaporation of the embryonic fluid. Among some species the external adhesive covering is very sticky and dries slowly. This is the case with the eggs of Longistigma caryae (Harris). It is not unusual to find eggs of this species covered with numerous grey or brown dust particles, especially if the host plant is adjacent to a dusty field or road.