Photo/IllutrationA beetle known as Pachyrhynchus infernalis (Provided by the National Institute of Advanced Industrial Science and Technology)

  • Photo/Illustraion

A weevil species in Okinawa Prefecture uses a parasitic bacillus to form an exoskeleton so strong that it can protect the beetle from pin pricks, researchers found.

A team of scientists primarily from the National Institute of Advanced Industrial Science and Technology made the discovery in Pachyrhynchus infernalis, a weevil around 1.5 centimeters long that is found on the Yaeyama islands in the southern prefecture.

The findings were published in the Proceedings of the National Academy of Sciences.

After the researchers removed a certain volume of the Nardonella bacillus from a weevil larvae, they found the adults developed a soft and reddish exoskeleton, said Takema Fukatsu, a senior researcher at the national institute’s Bioproduction Research Institute.

Normally, an adult weevil’s exoskeleton is much harder than those of other beetles. Researchers have difficulties sticking pins through the Pachyrhynchus infernalis for specimens.

The exoskeletons of insects are made of chitin and protein, but tyrosine, a kind of amino acid, is necessary for the chemicals to bind together.

Pachyrhynchus infernalis likely obtains a large amount of tyrosine from the Nardonella bacillis in its body, the researchers said.

“The bacillus is provided with nutrients and energy by its host in return for helping its host form the strong exoskeleton,” Fukatsu said. “The findings show the depth of their coexistence.”

A genetic analysis pointed to the possibility that Nardonella likely coexisted with ancestors of Pachyrhychus infernalis after infecting an egg in the female of the weevil more than 100100 million years ago.