Aphid Aggression

What am I looking at?

This is an image of an aphid on a leaf of a witch hazel plant. The aphid is the blue and red insect in the middle of the frame (1). You can see its stylet (2) – its mouth – poking into the leaf. The yellow and red structures in front of the aphid are plant cells known as trichomes (3), which form tiny hairs on the leaf. The other cells of the leaf (4), at the bottom of the image, are blue. This particular aphid is a first-instar wingless female known as a fundatrix, which hatches in the spring. It might be in the midst of feeding, but more likely it’s injecting a cocktail of proteins into the leaf tissues.

Biology in the Background

Aphids are small insects that feed on the sap of plants. They can be found across the world but are most diverse in the temperate regions of the Northern Hemisphere. Aphids have a relatively soft exoskeleton, but they have developed other forms of protection. In this case, they recruit the plant to help defend them.

These aphids feed on the underside of the leaf of a witch hazel plant, using their sharp proboscis to pierce the leaf and suck out sap. In addition, as they feed, they inject the leaf with their saliva, which contains a cocktail of molecular factors that alter the metabolism and growth of the leaf. These molecules force the leaf to grow around the aphid, encasing it in a protective cavity called a gall. Inside this shelter, the aphid reproduces parthenogenetically – meaning it gives virgin birth to winged aphids and these winged aphids fly from the gall to feed on the insect’s other host plant, river birch trees. Only the first generation of wingless aphids – the fundatrices - can form galls.

A wingless spring-generation aphid nymph is about half a millimeter long, or roughly seven times larger than the width of a human hair.

Technique

This image was created using confocal microscopy.