The following is a guest post from ESC student member Sharleen Balogh. Sharleen is a Masters student at the University of Northern British Columbia (UNBC) working with Dezene Huber and Staffan Lindgren on Warren Root Collar Weevils. She recently took home a President’s Prize for best talk at the ESC/ESS JAM in Saskatoon.
For the past two years, I have been studying the Warren root collar weevil (Hylobius warreni). These weevils are fairly large and long-‐lived (for insects anyways, they are about 12-‐15 mm, and live for up to five years). I think they are big enough to have distinct faces and personalities, although some people have told me that I’m personifying them just a bit too much and I need to take a step back from my work, but that’s another story altogether.
I am studying them because of their effects on coniferous trees, especially young lodgepole pines regenerating after the mountain pine beetle infestation in the interior of British Columbia. The larvae feed on the roots and root collars of trees, causing mortality of young trees and growth reductions in older trees (Cerezke 1994). They are native to the Prince George area (where I am doing my research) and can be found across much of Canada. They are often fairly common within their range. However they really can be described as “everywhere and nowhere”, since you can find them in almost any forested area in the region, just in low numbers and often well-‐hidden.
I have specifically been looking at the mechanisms by which they locate their host trees. The weevils can’t fly, so they walk along the ground in search of hosts. We know that they use vision (Machial et al. 2012a) to locate trees, but not much else about their host location. There are higher rates of attack by larvae on larger trees, but this could just be a result of a larger area of roots available, not an actual preference when finding hosts. So far no one has been able to find any chemical cues that they use, although this is very unusual for an insect. Some evidence suggests that at least in some situations their movements may be predominantly random and non-‐directional (Machial et al. 2012b, Klingenberg et al. 2010).
In order to study them, I decided to track the weevils using harmonic radar technology. This is the same technology that is used to locate avalanche victims. It functions by the detector sending out a signal in the microwave range that is passively reflected back by a transponder, attached to whatever you want to find. For use in locating avalanche victims, the transponder is the large Recco® tags you often see in ski jackets. In the case of the weevils, I used a miniaturized transponder– a tiny diode soldered to a 4 cm long piece of copper wire.
When I first decided to use this method, and to construct the transponders myself, I went online to learn how to solder. I was told by several different tutorials that it is “very easy, almost impossible to get wrong”. This may be the case when soldering computer circuit boards, but not so when soldering two tiny pieces of metal together under the microscope. In the end though, I did get it to work, and I tagged 115 weevils over two field seasons. I released them into individual plots in a lodgepole pine stand, within which I had mapped all of the trees, and I relocated them at regular intervals.
Although I’m still analyzing my data, my results suggest that the weevils preferred to go to closer trees, larger trees, and that the preference for larger trees increases when the trees are further away. Otherwise, their movements appear to be primarily random and non-‐directional. So, as strange as it is, maybe they do just use vision and random movements. If this is true, and their host selection process is predominantly random, this may have implications for forest management. It might make finding ways to limit their spread into new stands difficult, and it may make it difficult or impossible to identify potential genetically resistant trees for planting.
Cerezke, H.F. 1994. Warren rootcollar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae), in Canada: ecology, behavior, damage, relationships, and management. The Canadian Entomologist. 126: 1383-‐1442
Machial, L.A., B.S. Lindgren, R.W. Steenweg, and B.H. Aukema. 2012b. Dispersal of Warren root collar weevils (Coleoptera: Curculionidae) in three types of habitat. Environmental Entomology. 41: 578-‐586
Klingenberg, M.D., N. Bjorklund, and B.H. Aukema. 2010. Seeing the forest through the trees: differential dispersal of Hylobius warreni within modified forest habitats. Environmental Entomology. 39: 898-‐906