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Published: September 28th 2008
My final weeks in Canada were spent, crawling on my hands and knees, hands in the dirt, pulling weeds out of the ground in order to help my sister out with her PhD research. On the plus side - her project was located in the Okanagan valley, a very beautiful part of British Columbia. The landscape is similar to that of Central Otago, NZ (including the numerous vineyards). It's also the fruit basket of western Canada - loads of fruit.
The weed we were pulling out was Knapweed (Centaurea diffusa
), an agricultural weed in Canada, that probably slipped its way in with alfalfa sprouts. Andrea was actually more interested in the three introduced biological control agents of the knapweed (two that fed on the seed heads, and one that fed on the roots) and the interactions of these herbivores with each other and their host plant. The interactions between these agents could potentially decrease their ability to control knapweed. One of the goals of her research is to improve our understanding of how biological control agents may compete through their impacts on the host plant. This would allow for better selection of new agents, in light of those
She has a bunch of stuff planned but the questions the field work we did was to answer the following three questions
1. How do changes in knapweed population density affect the interactions between herbivores?
2. How do seed-head herbivores and pollinators interact to determine the seed set of diffuse knapweed?
3. What impact does adult feeding by the weevil
( Larinus minutus) on the stems and leaves of the plant have on the next generation larvae which feed in the seed-heads
Our focus was primarily on question one. At each of her sites we measured the density (using randomly placed quadrats) of the knapweed and dug up a sample of plants for further analysis in the lab (where Andrea will open up each seed head and root to count infestation rates). At Anarchist Mountain, field cages where used to determine the importance of one of the biological control agents Larinus minutus
acting as a pollinator for knapweed and whether Larinus
needs the plant to be pollinated to survive (Question 2). We hand pollinated the flowers in half of the cages, to be compared with the remaining cages. Half the hand pollinated cages and half
so those we didn't pollinate had Larinus
in them. Also at another site we took down a series of cages and harvested the plants where Andrea had been assessing seed set with a few different combinations of herbivores and pollinators. We dug up 200 plants for Question three that Andrea has been measuring and assessing the stems for adult Larinus throughout the season. She will now compare the level of adult herbivory to the number of larval Larinus she gets out of the seed-heads.
This field work wasn't without its hazards. The plant itself is spiky (cows don't like it much) and has all these tiny spines that embed themselves into your hands and then there's this cactus that if you walk anywhere near, will impale itself in you leg (or if your not careful then your bum) with spines 2 or 3 cm long. If that's not enough then there is always the danger of running into a snake or two (I only saw small grass snakes, but rattle snakes are also present). And then there's the ticks (think a spider that sucks your blood) which transmit Lyme disease and Rocky Mountain spotted fever But then if work
got too hot, then you could always go for a swim in the lake, or maybe sample the wine from a few of the vineyards.
Once we had finished the field work, Andrea left me in Penticton to explore. I went for a few walks among the vineyards and up a few of the hills surrounding the lake. Cristina and Francesca (whom I met in the hostel) hired a canoe paddled in circles (literally! - we never figured out how to make the thing head in a straight line) around Lake Okanagan. Cristina and I headed back down to Vancouver together, stopping off in Hope to explore bits of the Fraser valley. In Vancouver Andrea, Rich and I went for a couple of walks, explored the shops and I did a day trip over to Bowen Island.
Right now, I'm back in NZ. So this will probably be the last of my blogs. Thanks for reading them!
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