Photosynthetic Insects?

Over 3 billion years ago, some cells evolved the ability to capture energy directly from sunlight in the photosynthetic process. Photosynthesis is similar in all plants and bacteria and is thought to have evolved only once. The only photosynthetic organisms characterized have been plants and bacteria. Some interesting new evidence recently published in Naturwissenschaften (available by subscription only) by a group in Israel suggest that some insects may derive energy directly from the sun.

The oriental hornet, Vespa orientalis, has a yellow patch on its abdomen and an unusual cuticle structure that is a stack of 30 layers thick. This is intriguing because it brings to mind the structure of chloroplasts, the energy capturing organs of photosynthetic plants. Chloroplasts also have stacked membranes containing the the light sensitive pigment, chlorophyll. The cuticle of the oriental hornet does not contain chlorophyll, but it does contain another light sensitive pigment, xanthopterin.

Xanthopterin is a yellow pigment that creates a yellow stripe on the abdomen of the wasp. Usually, we think of yellow pigment on wasps as strictly warning coloration. Does xanthopterin serve a dual function of warning coloration and energy collection?

To test the ability of xanthopterin to serve as photoreceptive pigment, the team created a solar collector using a coating of xanthopterin as the light transforming dye. Upon exposure to light, the device was capable of producing electrical current and had a conversion efficiency of 0.335 percent. Xanthopterin is certainly capable of functioning as a photon receptive dye in an electron generating solar collector.

Does the insect actually uses the xanthopterin containing abdominal structure to create electrical energy from the sun? This is still uncertain. However, there are a number of pathways that could be used to generate ATP or store energy from this system. Enough is known about the system that solar collection is a possibility. If the hornet is collecting energy directly from the sun, what percent of its total energy is derived this way? If the wasp indeed is capable of deriving a significant amount of energy directly from the sun, this will change how ecologists think about food chains and energy pyramids.

Vespa orientalis with arrows pointing to areas of yellow pigment
Photo from: Plotkin et al., Naturwissenschaften Vol. 97 (2010) p. 1069.