Entomology, Integrated Pest Management

Episode 6: Biological Control in Relay Study

Join Emily as she talks to Dr. Jeff Bradshaw about biological control and what impacts that has in his dry edible bean and wheat relay study.

This transcript has been edited for clarity.

00:21 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’re talking to entomologist Dr. Jeff Bradshaw about conservation biological control and entomology, specifically in his relay plot study. So sit back, relax, and let’s go find out all about this.

So Jeff, can you explain what biological control is?

00:46 Jeff: So biological control is a part of integrated pest management. So it’s a tool – a tactic if you will – that’s used along with a number of other tactics in integrated pest management to reduce pest numbers, regulate those populations in a different way. So an alternative approach sometimes in a compatible way with other approaches, tactics, tools that might be used for for pest management .

01:13 E: What kind of strategies are typically used within biological control?

J: So generally speaking, there’s kind of three strategies to biological control. There’s classical biological control, which historically has involved and focused more on invasive species where you have a non-native insect – a pest whether it’s a pest of ornamentals or crops or other situations that a pest might arise in – that are introduced into the non-native habitat to that particular insect. And then you – the classical approach would be to go to the location where it’s native for the in the pest – in the case of the pest – you’d go to a location where the pest is native. And you would study and seek out the the natural enemies and maybe the parasitoids that might be highly specific to that species. And then there are a number of approaches then to introduce that that parasitoid, for example, into that new environment to try to see seek opportunities for control of that non-native species. So a classical approach is really focused generally on invasive species and trying to import those regulatory – regulating organisms into the environment.

Now the other approaches – augmentative biological control is where you have some understanding of what the pest’s existing natural enemy complex might be and you are releasing another natural enemy – such as a parasitoid – to augment or to increase the mortality of that pest through adding more natural enemies into the environment. And then conservation biological control is where you’re using different strategies or tactics in the environment through maybe changing the cropping system, rotation strategy, or some strategy that you might be using in the landscape – certain plantings of flowers or woody habitat maybe – that would provide habitat for natural enemies to to survive the winter or survive when the pest isn’t around. So three kind of general tactics um strategies that are considered in biological control.

03:31 E: What are the specific focuses you have within your study?

J: So currently, we’re looking at – we’re focusing on kind of two different areas of biological control. We’re looking at augmentative biological control with parasitoid wasps that attack the western bean cutworm and then we’re also looking at conservation biological control, primarily within the field, and looking at different strategies that we could use in cropping production systems that would bolster natural enemy populations; again specifically to attack western bean cutworm.

04:07 E: What are the differences between cover crop and relay biological control?

J: Relay cropping is a type of cover cropping. The main difference is termination time. So we’re looking at this study, our hypothesis is that if we have crops growing – we have something growing in the field before our main cash crop – dry beans in this case – that that

that that crop can provide habitat to natural enemies. So like I mentioned earlier, that would be a conservation biological control approach, and the main difference and the hypothesis we’re looking at is that the length of time that we have a crop in the field, in this case winter wheat, prior to our cash crop, dry beans, that length of time will influence the natural enemy population that is then available for the control of western bean cutworm. So in the case of the cover crop, we’re using a cereal winter wheat and we’re – we terminated that in late May, early June

as opposed to the release – relay system which is also using winter wheat as the cover, if you will, but instead of terminating it in June, we’re allowing that wheat to senesce naturally so that it will dry down and become ripe in around now – first week of July and so we think – there’s a possibility anyway – that that timing of when that winter crop is either terminated or senesces

naturally, will have an influence on the abundance and ecological function of those natural enemies in that system.

05:52 E: Can you share some of the arthropods that you expect to see within these systems?

J: Yeah, so the cover or relay crop in this case – uh winter wheat – is uh is a cereal and as a cereal, it can be a host to a number of aphid species like the Russian wheat aphid for example, and typically, those while – those insects can be very numerous and be economic pests in their own right in wheat. Generally that’s not often the case, at least in recent years, but they’re always present, so those aphids can serve as a food source for natural enemies so those would be lacewings,
ladybird beetles, big-eyed bugs, a number of different chewing or sucking insects that are generalist natural enemies that might attack aphids. We know they have a fairly large diverse diet and so they will also go after other pests.

So in the case of dry beans, what we’re hoping is of course, those those aphids are cereal aphids so they don’t go – dry beans aren’t a host for those aphids. So that’s a key aspect in the system that that helps make it work. Obviously, if the aphids in the wheat were pests of dry beans then we’d be setting ourselves up to a pretty bad situation. But in this case, again, the aphids aren’t compatible with the dry beans, but the natural enemies that they attract in
the wheat will feed on western bean cutworm eggs or thrips, either of which could be pests in in dry beans.

So our hope then is that we’ll have a early season establishment. Some of those aphid species for example, over-winter in wheat and so those can be available as a food source for those natural enemies as soon as they finish overwintering and start to come out in the spring. So that should give a lot of time for those natural enemies to feed, lay eggs, and build up those natural populations over time. And again, we would – our question is – that those populations might build up to larger numbers because they’ll have more time to develop in the relay system as compared to the cover crop system, at least under our conditions and the way that we’re looking at the system here.

And so timing wise, then we’re really kind of focused on the western bean cutworm – because it is a key pest of dry beans and as soon as – pretty close to when wheat senesces and typically is harvested in first or second week of June in any given year. That’s also really close to when we typically start to see one to five percent emergence of western bean cutworm and that can fluctuate given the year and the – you know the temperatures – and how they accumulate over the season. But that’s that’s kind of our goal is to try to target those natural enemies flushing off the wheat in high numbers to be present to uh – basically munch on those Western cutworm eggs that are are laid in dry beans.

09:03 E: You went into some detail on conservation biological control within your study. Can you elaborate a little bit on the augmentative biological control aspect?

J: Yeah, so the other part of our study we’ve looked at is augmentative biological control using Trichogramma ostrinae as a parasitoid of western bean cutworm eggs. And it was originally introduced into the US through a classical biological control program against the European corn borer. So that was a non-native introduced pest many years ago. And the biological control lab at Cornell University looked at this particular parasitoid wasp as a potential biological control agent.

Through the years, there had been some research, some science done looking at – um – the ability for that particular wasp to attack a couple other pest groups and we had done some early work looking at whether or not it would –
it found western bean cutworm eggs to be suitable, and we confirmed that they did at least in a laboratory. And then we did some field releases a couple years back, in – in cages to try to see if – in the field to see if there was uh any hope that there – you know if we showed it in a laboratory, but what you find in a lab doesn’t necessarily translate to what you find in the field. So we did sort of a semi-caged design in the field and kind of showed that yeah, it was still compatible host – the western bean cutworm eggs to trichogramma wasps there. So for a couple years, for three years actually, we did large-scale field releases on commercial dry bean fields and we used sentinel egg masses and sticky cards over – in every case a 10 acre square to look at the dispersal and dispersion of those wasps as well as their ability to attack western bean cutworms over that very large area.

And we’re still working on analyzing those findings, but generally we found that it seems like Trichograma ostrinae doesn’t really like Western Nebraska that much. It seems to work really well on the east coast, whether it’s green peppers or potatoes or sweet corn but for reasons we’re still sort of kind of fine-tuning what the next hypothesis might be as to why they might not work as well. But right now, we think it has to do with the environment, the climate that we live in is quite a bit different than than the east coast. If you’re not familiar with western Nebraska, it’s a semi-arid environment and semi-arid is definitely not how you defined upper New York state. So we think that probably plays a part in the success and why we had fairly low, fairly low parasitism rates.

12:12 E: Awesome, thanks Jeff. Folks, today we talked to Dr. Jeff Bradshaw about biological control and the different methods they’re using within the relay plot study. Join us next time as we go into more methods in these studies. Be sure to like this video, comment below, and subscribe to our channel for more updates. Visit our website at farmsci-ed.com for more videos and transcripts. Follow us on Twitter @theFarmSciEd for more information and for catching up on all those things you may have missed. Have a good one!