Having learned some valuable lessons from the pilot run (see last post); and encouraged by initial data analysis showing potential differences between both trap type, and plot; I decided to start the first run of trapping with subterranean and standard pitfalls at Brooms barn.
Unfortunately the grass was harvested just before my run, damaging and obscuring the traps in these plots; so for this first run we set out in just wheat and barley. Still, this comprised 14 of the 20 plots I will be using from the rotation experiment (see picture) and 42 traps of each type!
The weather conditions were still rather unfortunate, and combined with my long pole markers not being delivered (finding traps still time consuming), my gingerness under extreme high temperatures forced us to split the setting and collecting into two offset trap occasions.
The drought did provoke some interesting distinction in the trap types however: the standard pitfalls nearly all dried out, despite my entomologically expert assistant advocating extra water in in the trap fluid. This caused the traps to be filled with live specimens: particularly carrion beetles who were attracted to the rather ripe odours; an unanticipated pleasure for me, since they are so gorgeous!
This is a great comparison to the subterraneans that did not dry out, and had a pretty equal volume of coleopteran catch, including smaller and undamaged beetles, yet more general invertebrate catch (since live carabids predated). Whilst this run is obviously biased: I cannot know to what extent the subterranean nature of the trap affects the catch composition, against in-trap predation; it suggests a clear advantage of subterranean traps in drought conditions.
The time since the traps were collected on the 26th and 30th of July has been spent entirely counting beetles. So many beetles. Around 3,800 carabids. Identification has been a steep learning process, even given my past experience. I haven’t yet identified all the tiny ones, but I wanted initial data to present at an upcoming conference, hence the full on rush. A couple of tips:
- 1) Don’t rely on just one guide. Alex Greenslade of the Rothamsted insect survey kindly pointed me to Duff, which I found much more accessible than Luff, and some great online guides including mike’s insect keys (https://sites.google.com/site/mikesinsectkeys/Home/keys-to-coleoptera/carabidae). I found going between these sources was much easier and cleared up subjectiveness in singular interpretation.
- 2) Ask others. If you’ve been banging your head against a dichotomous key for hours, it’s easy to lose the plot. Chris Shortall and Dion Garrett, my entomological PhD colleagues, have been most benevolent in this regard.
- 3) Utilise past data/ collections. Consulting species records for Brooms barn gave me a springboard on a couple of species, and Alice Mauchline, my Reading uni mentor kindly lent me her beautiful reference collection of carabids, caught in agri-environments.
Though I have just started data analysis, I am already seeing some stark differences in trap type (incorporating those weather biases of course) and crop. I have also found some larvae, despite an overall dearth of soil moving invertebrates!
With so many traps I hope to pick apart some nice nuances, especially since the experimental plots comprise till and no till treatments… The next run should elucidate and further the distinctions, especially with inclusion of soil core samples and grass plots.
But if you want to know more you’ll have to wait awhile; or come and chat to me at Ento 18! https://www.royensoc.co.uk/event/ento-18