We used aspirators to catch the flies. The aspirators are constructed using two pieces of tubing attached to a glass bottle. When you breathe in through the tubing, a fly gets pulled in from the other side and is trapped in the container. In case you were wondering, there is a filter to prevent accidental inhalation. Unfortunately, after searching the Cardamine patches we didn't find many Scaptomyza.
It's a disappointing setback, but with any type of field work its always good to have a contingency plan. Nature will always do its own thing and won't necessarily coincide with the desired experimental conditions. Even if we can't get adult flies, we can still perform experiments with larvae. There are plenty of larvae to collect down by Emerald Lake.
Scaptomyza larvae normally feed inside Cardamine leaf tissue. However, they can crawl out and find new leaves to inhabit. It's possible that as the larvae feed, they may be tasting the isothiocyanates that form after hydrolysis of the glucosinolates. Since this is toxic to them, they may prefer to feed on Cardamine leaves with lower levels of toxins. We can present Scaptomyza larvae with Pseudomonas infected and uninfected leaves and see which ones they prefer.