You may start to feel sloth-like when the sun slips away during the winter months, but this little hornet actually derives energy (not just motivation) from sunlight, using its exoskeleton's nanostructures and pigments. Researchers first noticed something odd about the Oriental hornet in the early 1990s: Instead of being lazy-bums during the bright midday hours like other wasps, the Oriental hornet was extremely active. When the late entomologist Jacob Ishay started studying the hornets in 1991 he discovered some mind-boggling features of their exoskeleton, explains John Rennie at PLoS Blogs:
Ishay found that shining light on the hornets—live, anesthetized or even dead—could produce voltage differences of several hundred millivolts across their hard exoskeletons, which suggested that the cuticle material making up the exoskeletons was effectively an organic semiconductor converting light into electricity. Indeed, Ishay even found that shining ultraviolet light on an anesthetized hornet would wake it up faster, as though the light were recharging the insect.
The latest research
(pdf), reported in the journal Naturwissenschaften, was led by Marian Plotkin, who worked with Ishay before his death. Plotkin started by looking at the nano-level structure of the wasps exoskeleton, and found differences between the brown areas, which were covered in layers of grooves (about 500 nanometers apart, 160 nanometers high), and the yellow stripe across its abdomen, which was covered in flattened, oval-shaped structures (about 50 nanometers high) with "pinhole" depressions. These structures scatter the light instead of reflecting it, splitting it into beams that penetrate the deeper layers of the insect's exoskeleton, explains Gizmag
These beams proceed into the cuticle, where they encounter a several-layer-thick sheet-like structure. Within each layer are rod-like structures embedded in a protein matrix, the rods made from chains of the polymer chitin. It is this complex structure that keeps the solar light beams trapped within the cuticle, bouncing between layers.
But trapping the light is just the first step. To convert it into energy, the hornet's pigments come into play. As Plotkin tells BBC News
"The pigment melanin gives the hornet its dominant brown colour. The pigment xanthopterin, in the head and abdomen in a form of stripes and bands, gives the Oriental hornet its bright yellow colour," explains Dr Plotkin. "Xanthopterin works as a light harvesting molecule transforming light into electrical energy."
The researchers don't have quite enough evidence yet to claim that they've found the first photosynthetic bug, but they're working on it. Future work will try to determine if the hornet does change the energy captured into energetic molecules its cells can use, like ATP or glucose. Related content: Discoblog: Meet the Suicidal, Child-Soldier, Sexless Cloned Wasps
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Image: Wikimedia Commons/MattiPaavola