Canada Thistle Weevil as a biocontrol agent

A mating pair of Canada thistle bud weevils
Many of you know about thistles.  Nasty, spine equipped plants with attractive purple flowers, they are the bane of gardeners and farmers.  Creeping Canada thistle especially, as it will expand aggressively through root propagation and out-compete neighbouring plants.  Every pound of thistle in a farmer's field reduces the crop yield by two pounds.  You can imagine it wouldn't be long before an out-of-control thistle invasion would decimate a farmer's harvest.

Enter the Canada thistle bud weevil.  Although not equipped with red capes or flashy chest insignias, they are one of the heroes of thistle control.  Brought in from Europe in the 1960s, these snout beetles (weevils) were introduced as a biological weapon against the herbaceous pest.  Since then they have spread far and wide; I have encountered them in numerous places on my travels.  They are not the best natural tool for controlling thistle populations though; a relative, the thistle stem weevil, is far better at culling the plant.

I photographed this mating pair using a 105 mm macro lens on an APS-DSLR camera equipped with a pair of TTL macro lights mounted on the lens.  I have found this particular combination effective at capturing insects of modest to large sizes.  Smaller insects benefit from the addition of an extension tube on the lens or the use of a bellows with a reverse mounted 50 mm manual lens.

Thanks for reading.  www.ericspix.com

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