Pinus monticola and Leptoglossus occidentalis

Today’s entry is courtesy of Hannah Bottomley from Simon Fraser University, who has recently co-authored a paper on today’s subjects. We’ve Hannah to thank for the write-up and thermographic images and Stephen Takács for the conventional photographs. Hannah writes:

Pinus monticola (western white pine) cones glow warmly in contrast to cool conifer needles in the infrared spectrum (top right; bottom left). Cones can be up to 15˚C warmer than needles (as indicated by the temperature bar on the right) and emit significantly stronger infrared radiation. Infrared radiation is a type of electromagnetic radiation that the human eye is unable to perceive; it has longer wavelengths than visible light (380-750 nanometres), but shorter wavelengths than microwaves (1 millimetre to 1 metre).

These thermographic images of Pinus monticola cones were taken with an infrared camera, exposing a previously unknown way in which insects are able to hone in on their host plant. Recent research by Takács and his colleagues reveals that Leptoglossus occidentalis (western conifer seed bug) has infrared receptors and is able to exploit the difference between cones and needles in the infrared spectrum, and zero in on cone-laden conifers from afar. This insect is a specialist herbivore that feeds on the contents of developing conifer seeds; in the second photo, it can be seen feeding on a Pinus monticola cone.

This phenomenon of warm cones is not limited to Pinus monticola – it has also been observed in Pinus contorta var. latifolia (lodgepole pine), Pseudotsuga menziesii (Douglas-fir), Picea engelmannii (Engelmann spruce) and Larix occidentalis (western larch). It is attributed in part to the fact that larger objects retain more heat than smaller objects, as well as to the tendency of a cone’s surface to reflect solar radiation. In all likelihood, seed development (and associated metabolic activity) is also generating warmth, contributing to the relatively high temperature of conifer cones.

Although there are a few recognized infrared-detecting insects, this is the first study to show that herbivorous insects are using infrared emission from a specific part of a live plant as a foraging cue. This research is yet another testament to the complexity of plant-insect interactions and reminds us that there is a world of nature that exists beyond our own perception.

Daniel adds: For a popular summary of the paper, see “Heat Sensors Guide Insects to a Hot Meal” from ScienceNews. To view the scientific paper, see: Takács, S. et al. 2008. Infrared radiation from hot cones on cool conifers attracts seed-feeding insects. Proceedings of The Royal Society B. 276(1657):649-655. doi: 10.1098/rspb.2008.0742. For those of you who are particularly keen, I note that mast-seeding is mentioned in the abstract as a hypothesized method of producing a cone-crop large enough to exceed the capabilities of the insect herbivores to eat them all.

Horticulture / Garden Design link: Les jardins de Quatre-Vents, a garden I first learned about yesterday from the guide (thank you, Luana!) at Montréal Botanical Garden. Here are some photographs of the landscape and the plants. Virtual tours (in English) are available here: Virtual Tours of Les jardins de Quatre-Vents.

Pinus monticola
Leptoglossus occidentalis

18 responses to “Pinus monticola and Leptoglossus occidentalis”

  1. Sheila.

    Fascinating and amazing. Thank you for the pics and write up.

  2. Carole Miller

    And those photos may give a clue as to why some beetles and other insects are attacking our Southern Pines? Just sheer conjecture on my part.

  3. Lj

    Really fantastic pix. Thanks for this (new to me) knowledge!

  4. Patricia

    Very Cool!!! (or warm I guess) 🙂

  5. Bruce V.

    I wonder if this is one of those tip of the iceberg things: will botanists or etymologists see this seemingly everywhere they look? Will there be a revisiting of flowering plants as well?

  6. Hannah Bottomley

    Regarding bv’s comment: yes, I expect that scientists will soon be investigating whether or not pollinators are using infrared radiation emitted from flowering plants as a foraging cue. If you’d like to read a little more on this, the article touches on the subject in the ‘Results and Discussion’ section. This is all very new and exciting stuff – we really don’t know how widespread it is at this point! The fact that several different orders of insects are now known to have infrared receptors suggests that there may indeed be quite a few insects that are able to perceive infrared radiation emitted from plants, and utilize to their advantage.

  7. Mary

    Amazing and exciting! Thank you for sharing.

  8. elizabeth a airhart

    well i went outside to look
    at the pines i live in florida
    west central coast -and i looked
    at the pines in a whole different way
    some of the pines are growing what
    i call candle sticks and i did wonder
    how do the tne pollinters find the plants
    perhaps just not instinct and how did
    that happen

  9. A

    warm pinecones, totally strange, amazing and unheard of! I learned something new today!

  10. Arian Ndoni

    What the physyological process inside the cells of the cone? Is any explanations? The articel and photos are wonderful. Deas this phenomena happens to all Pinus sp, or only on P. monticola?

  11. phillip

    …we are but babes in arm tryin to decipher the complexities of our nature…

  12. A

    wow philip, that’s exactly what I think! it’s amazing the new things around every corner!

  13. SoapySophia

    Amazing it is that hot! It like, 25 C in the center of those things, or am I reading it wrong?

  14. Liz

    What are the implications of climate change on the sensing mechanisms of the insects? How can we use this knowledge to increase food protection and productivity?

  15. Chungii V

    I wonder if this is why some species seem to attract more insects than others?

  16. Equisetum

    Wow, what germinal questions, bv and Carole and Chungii!

    I wonder how much an infra-red sensor costs… we could be doing backyard research.

  17. Hugues CREPIN

    Very interesting article, shared and included on the Thermograpic’s Library, résumé in french (

  18. Hugues CREPIN

    One little detail I omit is that you don’t take into account the fact that cones and needles have probably not the same emissivity. Ok, no importance for the insect who will perceive it the same manner but only about the claimed 15°C of temperature difference who could be quite different.

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