Bugs Find Meals With Heat Sensors

The western conifer-seed bug, Leptoglossus occidentalis, has a peculiar world view. Objects stand out against the background as a result not of their color, but of their temperature — and the infrared radiation that comes with it.

Trees, warmed by their active metabolism, appear as if on fire, and their even warmer reproductive organs — in conifers, the cones — seem to glow like embers. The bugs navigate this thermoscape using infrared receptors to locate the precious seed-bearing cones they feed on.

Stephen Takács of Simon Fraser University in Burnaby, British Columbia, and several colleagues discovered the novel system after noticing that conifer-seed bugs are often attracted to warm objects in people’s homes.

To find out more, the team first measured the temperature and radiation of different pine-tree parts. Cones were as many as 27 Fahrenheit degrees warmer than needles and emitted proportionally stronger infrared radiation. Then, they tested the ability of conifer-seed bugs to perceive the radiation. Placed in cooled experimental boxes, the insects were offered the choice of a strong or weak infrared source. Insects overwhelmingly chose the strong radiation. Electron micrographs of the insects’ abdomens revealed eight bristly organs that, when irradiated, responded with frantic electrical activity. Moreover, when the presumed receptors were covered, the bugs lost their infrared “vision.”

Takács and his team suspect that many other insect species can sense infrared, and that some plants use the radiation to advertise to pollinators.