The Peak

Hot cones a hot commodity for seed bugs, SFU researcher discovers

By Stephanie Orford, Associate Staff Contributor

Imagine being able to detect heat from afar as if your eyes were an infrared camera. A research team led by Simon Fraser University’s Dr. Stephen Takács has discovered an insect that can do just that — the western conifer seed bug. Unlike any other known organism, the seed bug uses this special sense to forage from afar for its favourite food, the seeds that grow inside conifer cones. Dr. Takács and his research team’s discovery could help the forestry industry in B.C. deal with these pests, which have been shown to destroy up to 95 per cent of the seeds of the trees they feed on.

“Because they’re a pest species we wanted to understand their biology and their ecology in order to somehow fool them into doing what we want them to do, as opposed to doing what they want to do,” said Dr. Takács. “Right now the only thing the orchardists can do is walk through the orchards, try to find [seed bugs], and as soon as they see one, they start spraying. They have no idea whether they have one, or whether they have to spray the whole orchard because they’ve got a million.” Dr. Takács suggest that orchard owners can use infrared radiation-emitting traps to catch seed bugs, so they can estimate how many inhabit their conifers, and whether they are a threat enough to make pesticides necessary.

Dr. Takács’s research team tested seed bugs in laboratory experiments at SFU and in field experiments conducted in conifer seed orchards in Sechelt, Kalamalka, and Schwartz Bay B.C., and found that the bugs were significantly more attracted to areas emitting IR radiation than to areas that emitted relatively low IR radiation. In other words, when the seed bugs were offered a choice between an area that looked warm and an area that looked cool, they nearly always headed toward the heat. These results strongly support the idea that the seed bug possesses some kind of IR detection sense.

When she tested the various conifers the seed bugs feed on, Tracy Zahradnik, a PhD student and researcher on the team, found that the cones were up to 15°C warmer than the needles and their surroundings. The heat and IR radiation coming from a cone are produced by a combination of reflected IR rays from the sun and heat generated by the busy metabolism of the seeds growing inside. When Zahradnik imaged the conifers using an IR camera, they lit up “like Christmas trees,” said Dr. Takács, with the cones appearing bright against the rest of the tree and its surroundings.

According to Dr. Takács, this is similar to how the seed bugs perceive the tree. The bugs detect the IR radiation, which the cones produce along with the heat they emit, so they can sense the radiation from a long distance away, even when they cannot feel the heat that would normally accompany it at close range. This means that the seed bugs can forage not only during the day, but at dawn and dusk, when humans cannot easily visually distinguish objects, but when the cones are still warm.

When the researchers used an electron microscope to look closely at the bugs and what kind of sensors they use to detect IR radiation, they found IR sensory receptors located on the sides of the insects’ bellies. The exact nature of these receptors is still a question, among many others, that the researchers would like to tackle.

Another question Dr. Takács and his team will continue to pursue is whether there are other species of insects that can detect IR radiation. A few insects and animals are currently known that use IR detection to survive, such as the Australian fire beetle, which uses IR radiation to detect where a forest fire has been so it can lay its eggs there with no threat of competition; or the vampire bat, which uses its IR detection to locate the warm-blooded animals that provide its blood meals. Dr. Takács and his colleagues think these few known species might be the tip of the iceberg, and the researchers are interested in finding more species that have an IR radiation sense. In the future they might investigate blood-feeding insects, as well as the flies and moths that also feed on the cones in the same orchards inhabited by the seed bug. “We want to know, are [the flies and moths] finding these cones in the same way [as the seed bugs]?” said Zahradnik.

Put into practice now, these findings could help seed growers whose conifers are plagued with seed bug infestation. Seed bugs have spread to Eastern Canada and have been found as far afield as Italy. Dr. Takács suggests the possibility of using IR-emitting traps to catch the bugs before they can devour the seed crops earmarked to become seedlings used for tree planting.

The research was conducted over three years through the lab of Dr. Gerhard Gries in the SFU Biology department, and also involved the work of researchers Hannah Bottomley, Iisak Andreller, Joseph Schwarz, Robb Bennett, and Ward Strong. The findings were published in a recent issue of Proceedings of the Royal Society B.