Jeff talks with Emily about insect sampling and collection for his entomology studies.
This transcript has been edited slightly for clarity.
0:23 Emily: Hi everyone, and welcome to Farm Sci-Ed, the show where we go into the science and education behind farming. I’m Emily Stine and today we’ll be talking to Dr. Jeff Bradshaw about entomology sample collecting and the different processes he uses to get samples. So sit back, relax, and let’s go see what Jeff uses in the field.
0:42 So Jeff, can you explain the importance of sampling to entomological research?
Jeff: Insect sampling in general has a couple purposes, when it comes to pest management at least and some other disciplines as well, but there’s sampling for research essentially, and then there’s sampling to make a decision as in applied field crop pest management, and then sometimes you’re doing sampling for research for the purpose of making the decision. So the reason that’s important is there’s different levels of intensity of sampling that you might use, depending on if you’re a crop consultant and you’re trying to you know make efficient use of your time and not spend a bunch of time in the field sampling, you just need to make a decision at some level that you’re comfortable at versus when you’re doing sampling as a researcher – as a scientist – and you’re trying to use that data for other purposes, to learn more about the insect, when it occurs, how to control it at a high level of accuracy and precision.
So um sampling then for our study and for anything is one. There’s different tools that we use for sampling and then the purpose of the sampling. In our case, we’re collecting a number of different species and then using that sample to identify which species are present and then how many of those species are present within the sample.
2:06 E: What are the differences between sampling types?
J: Yeah so one other difference uh between sampling methods as I mentioned earlier: sampling for research or sampling for a decision. A lot of times we’re doing sampling for research, we’re using more than one tool. Basically attack a problem – if you will – from more than one angle, which is very common in science. Use more than one kind of method that you’re asking for, which you’re addressing, the same question because every sampling technique and tool has a slightly different bias, maybe towards different species or towards different catch efficiencies. Yeah, really what you want to do for research is you want to capture – kind of encapsulate all the different methods that you can, to try to see well, at the end of the day, if you have more than one sampling methodology or tool that you’re using, and they all kind of point in the same direction ultimately with their data, in terms of the conclusions that you can make, then you have a much more powerful conclusion because you have more than one method that you use to to arrive at it.
3:05 E: What do some of these methods look like?
J: Some of the methods that we’re using – specifically to our study – are vacuum sampling. So we have a leaf blower, which we put on the intake side of the leaf blower to use as a sucking tool and uh we cover the end with a mesh, and then move for a certain – well there’s different ways you can do it – you can move through a canopy for a certain period of time or certain distance or a combination thereof, so you have a standardized way of collecting with that tool. And so it sucks everything into the mesh and then you close the mesh around the around the sample and then put it into a plastic bag. So we’ve got vacuum sampler, got a sweep net that we use kind of similar type of sampling, you’re sampling the canopy of the plant just like you are with a with a vacuum sampler.
We have sticky cards that we leave out for a period of time and we’re targeting aphids or minute pirate bugs, aerial insects that are moving through the air and some of which are attracted to that yellow color color of this yellow sticky card. Then we use pitfall traps to ensnare organisms that are running across the soil. So essentially it’s a little more fancy than that, but it’s essentially a hole in the ground um and then the insects fall into the jar that’s within the hole and then we can pull the sample out of that.
And then we have pheromone traps that we use and those are much more specific. In this case, we’re using a pheromone to target the the pest of preference, in this case western cutworm and to trap them and to use that as just a general sampling tool to try to understand what their numbers are. And then a black light trap that we use again for for sampling purposes, and our purpose black light trap is really we’re trying to collect egg masses ultimately um from the western cutworms that are being attracted to that black light trap. And then other – you know – all those sampling tools are looking at ways to capture and then ultimately identify and count the specimens that are the species or organisms and numbers of organisms that are within the plot.
But we also have tools that we use to sample function, different tools that we use to sample function would be like sentinel prey. So we might use sentinel egg masses – so for example with a black light trap, we sample adults and then we go into the black light trap and we gather the females in the trap – well actually, gather all the western cutworms that are present in the black light, drop and then release them into a cage with corn or dry beans um and then give them 24 hours to lay eggs.
And we use those eggs that they lay on the dry bean leaves or on whole plants and we put those out into the field and then measure over a 24 hour period how many eggs are gone. You can put the eggs underneath the microscope and determine whether or not they’ve been sucked dry by a piercing insect or whether they’ve been chewed off by a chewing insect. And so that gives you just greater insight, not only the predation but maybe the type of predators that would be present and so that would sample the insects that are moving through the canopy of the plant.
Another layer of sampling would be to functionally sample the insects that are on soil – that we would use wax worms sometimes affectionately referred to as “truffles.” The way we lay out – basically clay um modeling clay with a pin that we attach the uh the wax worm to and then we leave it for a period of time, sometimes overnight, and then just we’ll have them in open cages and closed cages to expose them to the predation within individual plots. And then again, the the the data it will glean from that would be – you know – is the waxworm after 24 hours alive or dead? Is it still present? Has something ripped it off of the the pin and carried it off? um Has a piercing insect attacked it again? You can gain all those insights by – you know – kind of studying the specimen that you left, the sentinel prey that you left out with a microscope.
7:37 E: And what do you do with the samples after you’ve collected them?
J: All these different sampling methods whether we’re sampling for counts or sampling for function um take a lot of time. When we’re we’re sampling for individuals, like with the sticky cards or vacuum sample, you end up with a collection of individuals and so you have to go through the sample and identify the specimens that are there. Typically you’re not necessarily looking for everything that’s in the sample – sometimes you’re targeting specific groups or maybe specific orders.
And then at some point, you’re making educated estimate on which of those species might have high enough counts to give you some measurable differences when you start comparing treatments that is. If you have an extremely rare thing that only occurs in one sample, and it’s like one species of something that you’re you’ve rarely ever seen the sample, well, when you look at the data you’re going to have one and then a bunch of zeros and you can’t do anything with that comparatively. Whereas you may have a group – like when we’re sampling um for pitfall samples for example – again you have a bunch of insects in that sample, we know from prior research and prior soil sampling type work that ground beetles are typically have a lot of species or you can capture a lot of species with that method. And so that that family of beetles we might look specifically for and identify them to species, because we we think that that could tell us more, because we have more data associated with – this has more species or the species change between plots, where the numbers of individual species change between plot can then tell you something about either the habitat or the growth form of the canopy and different things different insights you can glean from that.
So when we collect them, they’re generally dead or we freeze them and make them dead. But generally we’re looking we’re looking at dead insects that we’re then counting. Sometimes on the sticky cards they might not be. The only sampling methods that we’re using where we’re actually looking at live insects are with the black-like trap sampling and again we’re we’re looking to keep them alive, so that the female moths can lay eggs and the eggs are alive. And so the sentinel eggs that we put out are living eggs, they’re not frozen so they they would be viable enough that they could even hatch within the plots and that again can give us some insight about that treatment and whether or not it had enough predators to kill enough the eggs that the larvae don’t hatch versus plots where you didn’t see that predation, now you have an infestation of western cutworm larvae that can then injure injure the plots.
10:45 E: What is the intent of all this collecting?
J: Yeah, so you know first we sort through it and there may be specific groups that we’re targeting. Within those specific groups, we might um identify them further to species uh or maybe the genus only and then from there you end up with a large database for each plot. Typically we might have three, four, maybe sometimes five sampling periods, so you could take that sample and repeat it throughout the season so you can multiply the numbers even more. And so so our data sheet would look like certain numbers, certain numbers of individuals, a certain species by date.
And so what we then hope to learn from that or things that you can learn are how treatments might impact the occurrence across the season of certain species. So in our wheat relay, or wheat only, we might anticipate the presence of cereal aphids and we might anticipate that they might start out pretty low in the season and increase as the wheat grows, we have more and more of those aphids and then once we harvest the wheat, probably won’t see that many of those aphids anymore since they’re pretty specific to grasses, in some cases fairly specific to wheat and and closer associated grasses.
So um so then that relationship we see with the with the ebb and flow across the sampling dates of the aphids, we can then look at the data set that has our predators and see if they track along that same line and whether or not there’s any relationship between that seasonal change in aphid numbers and the predators that are present in the field to see if kind of one begets the other, in a sense. We look across the season, we see an increase in pests and then the predators track in association with that increase and then we harvest the wheat. And those um across the season we can see that those aphids now are no longer present, but maybe the um predators stick around and then we can start to see if then those predator numbers that have maybe stayed in those plots after the wheat’s gone shifted over to western bean cutworm, or if that changed the nature of the predation rate of the sentinel egg masses, or if it changed the predation rate as a result of our wax worm truffles.
So once you have the data, there’s different ways of looking at it, you know. We could look at the species diversity of the predators, and see if that changed. We could look at species numbers to see if that changed by treatment. Obviously you could see if the treatments had no impact on either those whatsoever. And then we could – we’ll also look at correlative items like relationships between prey and predator and if any of those relationships changed as a result of the treatment or not.
13:58 E: What are you hoping to learn from it?
J: Yeah, so once we have that data set and we look at those relationships, we can look at higher order relationships between those ecological functions that we were trying to measure – the individuals and and species diversity we’re trying to measure – and see if there’s if they track at all with the yield that is reported out from the plots or the injury that we see on those beans. And usually there’s um obviously there’s a lot of variables in the field, a lot of other variables contribute to yield and quality other than just the things that we’re measuring. So typically what we would do is constrain the conclusion that we’re trying to make, so we don’t overblow the conclusion. We can say, well, this proportion of the population can account for 30 percent of the yield increase or accounts for 10 percent of the damage that we saw. We can say it’s related to this relationship.
14:50 E: Well folks, there you have it. Today we talked to Dr. Jeff Bradshaw about entomology sampling and what he does with the samples he collects from the field.
Join us next time as we go into more depth on our other topics in plant pathology entomology and weed science. Follow us on Twitter @TheFarmSciEd, be sure to check out our website at farmsci-ed.com for transcripts and more information about this program. Have a good one!