Control insect pests on your land in NSW

Introduction

Good afternoon everyone and welcome to today's webinar: Crop Aphid Identification and Management, brought to you by Local Land Services Central West and Central Tablelands in collaboration. This webinar is part of the Central West LLS Ag Services Adapt Project. This project is supported through funding from the Australian Government's National Landcare Program.

I'm Rowan Leitch, the Mixed Farming Advisor with Central West LLS, and together with my colleague Liz Davis from Central Tablelands LLS, we've invited the experts from Cesar Australia to present on aphids and their significant impacts on agriculture in the southeast of Australia. This is part of a series of webinars Cesar will present on behalf of LLS, so keep an eye out for them in the coming months.

Before I introduce our guests, I'd like to begin by acknowledging and paying my respects to the Traditional Custodians of Country throughout Australia and their connections to land, sea, and community. We pay our respects to their Elders past and present and extend that respect to all Aboriginal and Torres Strait Islander peoples today.

I'd like to welcome Dr Lizzie Lowe from Cesar Australia as today's presenter. Lizzie is a Senior Extension Scientist with Cesar and is based in Sydney, with sustainable insect management and biodiversity conservation the core focus of her research. Additionally, we also welcome Dr Zaritsa Jurich, New South Wales Department of Primary Industries Field Crop Entomologist based in Tamworth. Zaritsa will present on the management strategies currently being advised to producers in New South Wales.

I'll hand over to Lizzie to begin today's webinar.

Presentation

Thanks very much Rowan. What we're going to be covering today: I'm going to be talking about basic crop aphid identification because it's not an easy thing by any means, and a little bit of information about insecticide resistance issues because this can have a huge impact on how you manage these pests. I'm going to quickly talk about some really cool research that we're doing into alternative management of aphids, and then Zaritsa is going to talk about management of aphids in pulse crops in New South Wales with some great examples and a little bit about virus transmission.

I welcome you all to write questions in the chat as well. I've got quite a few links which I'll be putting into the chat, and feel very free to write your questions in there. We will come back to them at the end of the presentation.

Why Do We Care?

So why do we care about aphid identification? They're very small and can be very daunting to identify. There are over 150 species in Australia, so it's no wonder that people often find aphids very difficult to identify correctly. But it is important. Firstly, something that I'll talk about in more detail later is that we do have insecticide resistance in some species such as green peach aphid, so it's really important to know which species you're dealing with. There are also differences in the damage potential of different species, and some species can transmit viruses whereas others don't. There's also different damage by different species at different crop stages, so even if you have quite a large infestation of some species, it may not actually result in any economic damage depending on the crop stage.

Some of the most important features that we use for identifying aphids are what I'm going to run through quickly with you this afternoon. There are lots of different parts of the appearance which I'll talk about, but also one of the really key things is the host. If you know the host and you know a little bit about identification, it's actually much easier to drill down into what species you've got.

A quick talk about aphids: they're not just small but they're complicated little critters because they've got lots of different life stages. When they are juveniles, called nymphs, they're very small and they don't have wings. Adults can be either winged or wingless. Basically, you don't want to be using small juveniles for your identification because they have quite different identification features than the adults. Sometimes you also don't want to be using the winged adults. So when you're looking at aphid identification, you'll often have all four of these different groups all together, but it's best to focus on the adults. The largest ones that you can find without wings are the best for the identification features we're talking about today.

One of the first things that we can look at is body shape. We do have quite a range of different shapes in aphids, and it's one of the most obvious features as well. If we use the Russian wheat aphid and the oat aphid as an example, you can see the long spindle shape of the Russian wheat aphid, which we'll talk more about later, and the oat aphid is quite round and globular. It's quite obvious when you see them next to each other—obviously not quite so obvious when you've just got one by itself—but it's a good comparison if you've got multiple species.

Secondly, one of the body parts that we can look at on the aphid is called the siphunculi, or the exhaust pipes, on the very end of the abdomen. They change quite a lot in color, length, and positioning. For example, the cabbage aphid has tiny little exhaust pipes that don't even reach the end of its body, whereas the turnip aphid has slightly longer ones, and others have quite long siphunculi that extend beyond the end of the body. So that's another identification feature we'll be using to look at different species. I should say this is just me going through all the features, and then we'll get into it with different types of species—so don't worry if you don't know a cabbage aphid from a turnip aphid at this stage.

The other part at the end of the body is the cauda—basically the little tail at the end of the aphid. You can see in this video here that one aphid has a bifurcate (two-part) tail and another has a longer tail. Again, different colors and shapes occur in different species of aphid.

The antennae can also be a really good diagnostic feature. You can see the example here of a very short antenna aphid and a longer one, but it's also very difficult to see sometimes. So when you're looking in the field, you can almost see the antenna here. There is also something called the tubercle, a tiny little gap within the head, but even if you use a hand lens like the ones Liz has sent out to lots of you—if you haven't got your hand lens yet then you can have a chat to Liz—it can be very hard to see the tubercle. So we don't talk too much about that, but if you send it into a lab that's often something we'll look at as a diagnostic feature as well.

Now if we move away from what they look like, behavior can be a really important indicator as well. Something like green peach aphid is often much more sparsely distributed—they're not as social and will move around in individual groups—whereas the cabbage aphid will often clump together. They form quite dense colonies and give off a kind of white powder as well. So we can look at how they're moving around the crop and where they're situated with other aphids as well.

Of course, you can also have lots of different species of aphid, which can make it complicated. Feeding damage is another one that we look at. The Russian wheat aphid is a really good example of this because they have that characteristic long purple striping feeding damage that you can see, and a corn aphid causes the leaves to twist up.

Now, if we actually try and think about determining which species we've got, I've now told you what kind of tools we use. Now I'll be actually making the comparisons. The way that we break it down when we do aphid identification is by looking at the host plants. If we can break it down into what host they're on, then there's usually only a choice of about three or four main species that you're most likely to be dealing with. We can use this to narrow it right down and make it much easier to identify them because the three or four species within each of these groups do have quite major physical differences which we can use. I've got an article from our website that's written up about this as well, which I can put in the chat afterwards for you to refer back to.

Cereal Aphids

If we look at the cereal aphids, we've got oat aphids, corn aphids, and Russian wheat aphids, which are most common in cereals. Very superficially, if we just look at them, body shape is the first thing that jumps out at us as being quite different. We've got the Russian wheat aphid, which we call a spindle-like shape. We've got the oat aphid with that big round body, and we've got the corn aphid with a kind of rectangular shape. So straight off, just looking at body shape, if you've got an aphid on a cereal, that's one way you can use for looking at the differences.

If we focus in on the oat aphid, they also have a mark at the bottom of their abdomen down here—it's kind of a reddish patch at the base. They've got quite blunt siphunculi and medium-length antennae. If we switch over to look at the corn aphid, they've got a slightly different pattern here. They have these dark patches at the base of the exhaust pipes, and the exhaust pipes are a little bit longer and instead of being blunt, they've got a tapering tip and a very oblong-shaped body.

Russian wheat aphid, which many of you might have come in contact with before, has much shorter antennae with little black tips on them. They've got that spindle-shaped body, which you can see here. They have very small siphunculi or exhaust pipes compared to the other two, which were quite a bit longer, and they often have this kind of dusting of wax—this white waxy substance—on them as well.

I will just put in briefly here with Russian wheat aphid management: a tool that can be really useful here is called the Russian Wheat Aphid Threshold Calculator. If you haven't heard of this before, it was developed by Cesar as part of a GRDC project and is based on the GRDC Russian Wheat Aphid web page, which again I will paste in the chat when I'm finished speaking. We can use this calculator to decide whether it's economically justified to spray for Russian wheat aphid because it varies very much with crop stage and with market price. What you need to do for this calculator is input the expected cost of how much it will cost to buy the chemicals to control them, the yield potential, and the market price. This little calculator will then calculate whether it's actually going to cost you more to control than it would save you to leave them in the crop at that stage. This is a really useful tool to make sure that you're not spraying if you don't need to.

Pulse Aphids

Moving on to pulse aphids, we've got three quite different-looking aphids here: bluegreen aphid, cowpea aphid, and pea aphid. These bluegreen aphids, which we will be talking about a little bit more later because they're quite a significant pest, have very long antennae, very long siphunculi, and a blue to gray-green color. The cowpea aphid is quite distinctive because the adults are almost black. The nymphs—the smaller aphids—are kind of a dull gray color, but you'll often see these black-colored aphids, and they do have white banding on the legs, so they're quite distinctive. The pea aphid has these really funny black knee joints compared to the bluegreen aphid, and they're also a slightly different color as well. So that's the main distinguishing feature there.

Canola Aphids

Finally, looking at the comparisons with the canola aphids, we have the green peach aphid. This is where the siphunculi can be used as a diagnostic feature, but again you probably won't see that much when you're out in the field. We've got quite a teardrop shape here and the long siphunculi, so if you're looking in canola then that's one of the main features you're going to be looking at there.

Turnip aphid is quite different to some of the others in that they've got these long dark bars across the abdomen. They've got this quite circular round abdomen as well, and you'll see it more when they're side-on because they're quite bulbous. They've got small siphunculi. Even smaller again is the cabbage aphid, and they're quite a distinctive color as well.

Green Peach Aphid

A note of warning: in species such as the green peach aphid, color can be really deceptive because they change color depending on the time of year and what they've been feeding on. So this can be quite a difficult feature to use as diagnostic, so don't always just rely on color. It also depends on what stage they're at. If they've recently shed, then you won't have some of those features like the powdery color or some of those bars.

Getting back to talking about green peach aphid: this is one of the really key areas where identification is important because if you have green peach aphid in a crop and you spray it with the wrong type of insecticide, you may not have any effect if resistance is present, and you may actually make resistance worse by developing resistance in an area that it previously wasn't.

If we look at the data we've got from 2019, we can see that there's quite widespread resistance in green peach aphid to both synthetic pyrethroids and carbamates. The red dots are where there's already resistance, and the yellow dots are where the populations are showing evidence that they may develop resistance. A similar story in organophosphates: quite a few resistant populations, especially in northern Victoria and central New South Wales, and also to neonicotinoids—quite a few centered down in southeastern Australia. So definitely something to keep in mind: making sure that you've got the right identification for green peach aphid and that you're not using a spray in an area where resistance has already developed.

Sulfoxaflor is an insecticide that can be used against green peach aphid, but we're also seeing shifts towards resistance here. This figure shows what resistance looks like in Europe, where there are quite high levels of resistance. You can spray them with very high concentrations and they still have low mortality. This is what general mortality looks like—what you would expect if there was no resistance—and we're already seeing a shift towards more resistant populations in Esperance. So it's another one that's going to take another insecticide out of our toolkit if this develops resistance. We have to be very wary about how we use them.

Test for Resistance

Insecticide resistance testing is conducted at Cesar Australia, and we rely on agronomists and growers out in the field who report back to us and send samples. One of the really important things for green peach aphid is to actually test for resistance. We have an aphid insecticide resistance testing service, and this is free. It means that we can stay on top of where the resistance is and report back to people in the field about what kind of levels of resistance are in the populations in their fields.

So if you have had a population of green peach aphid which has survived a chemical application, or it's suspected that they might be chemical resistant, or any other aphid species present when there is a control failure—meaning you spray and the aphids aren't affected by that spray—we'd really love to hear from you. We would love to get some samples to test. You can get in contact with me or Samantha Ward. I'll put her contacts in the list as well, and we'd really appreciate anybody that's had any experience in this area to reach out and hopefully provide some samples.

Biological Control

Let's talk a little bit more about what's my passion, which is the non-chemical methods of control. Aphids are a really interesting example because there are lots of fantastic biological control agents which you can use. These videos here are my favorite because you can see a ladybird at the top really chowing down on some of those aphids and a lacewing larva down the bottom. We've also got a huge range of parasitoid wasps and lacewing species. The parasitoid wasps are the ones that will actually lay their eggs inside the aphid, and the wasp then grows up inside and then hatches out, killing the aphid. This is just another reason not to be spraying any old pesticide on your fields because then you'll wipe out the natural enemy community as well, and you'll have a much greater problem with dealing with these aphids over time.

Another thing you can do that will really help with aphid management is keeping an eye on the green bridge. This means two to three weeks before sowing, making sure you've reduced that green bridge around the field. There are many different weeds which are host to aphids such as green peach aphid, capeweed, ox-tongue, wild radish, dogwood, and dandelion. So making sure that you're on top of the green bridge and you don't have too much of a refuge there for them can really affect the numbers of green peach aphid that will come into your crops during cropping season.

If we're talking about trying to limit resistance as much as possible, these are the six key things that you need to be thinking about:

1. Monitor at the critical period – Keep an eye out for these particular aphids at the right time of year, which is all in the resistance strategy down the bottom there.
2. Correctly identify the pest – Make sure you are actually dealing with green peach aphid if that's what it is.
3. Rotate insecticide groups – Instead of just spraying the same chemical active over and over again, rotate groups. Resistance develops when individuals survive and pass it on.
4. Use selective insecticide groups where you can – Use ones that are targeted as much as possible to the pest, which allows natural enemies to come in and help with pest control.
5. Reduce the green bridge – As discussed earlier.
6. Use cultural management such as beneficials – Encourage natural predators.

Again, there are two other links which I'll send out to you. If you have had problems with green peach aphid or resistance, then these are really useful documents for you to have a look through.

Endosymbionts

Finally, I'll just tell you quickly about some really cool and exciting new research that's coming out of Cesar and the University of Melbourne at the moment. We have a big research project called the Australian Grains Pest Innovation Program—our AGPIP program—and one of the projects within this is about endosymbionts. You probably haven't heard about these before, but they're tiny little bacteria which actually live within the cells of other organisms. In aphids, these endosymbionts, which are living within the cells, can actually affect how these aphids respond to things like insecticides, variations in climate, viruses, and predators. So those little cells in there can mean that they survive differently under different conditions.

This means that by manipulating these bacteria, you can actually increase susceptibility to insecticides and natural enemies. So if you have a population which has become resistant to a particular pesticide, you can actually treat them with something like an antibiotic that kills off these endosymbionts, and then the population becomes susceptible again. It's a really interesting new area of research, and there's huge potential here as well. It's a very complicated system because there are lots of species of aphid and lots of species of bacteria, and they have lots of different interactions with the environment. But it's a really exciting way that we could be limiting the amount of insecticides that we use by manipulating the biology of these species.

Community Involvement

Like I was saying before, this is a research project that really relies on people in the community helping us out as well. We really rely on those growers and agronomists that are out there seeing these aphids, and we're always looking for new relationships to test between these aphids and their bacteria because we've already discovered a really wide range of examples of where these bacteria can have an effect. So if you do have any old type of aphid that you feel like sending into us, we're discovering new bacteria all the time. I'd be really excited to hear from you if you have some that you could send in.

I will stop there and stop my sharing. I can put my links into the chat for you and hand over to Zaritsa.

Pulse Aphids and Virus Management

All good, you can hear me? Okay. As you heard, I will tell you today something about aphids, especially aphids in pulse crops and the potential virus management.

Among other aphids that are present in pulses and in canola and oilseed crops, there is one aphid that's pretty important—that's cowpea aphid. Cowpea aphid is primarily a pest of faba beans, then lupins, medics, lentils, vetches, but also lucerne and clover. This aphid is often first observed along crop edges, and their infestation can be patchy inside the paddock. This aphid also, as you can see from the picture below, likes tips of young plants, like you can see on this picture with the young faba bean plants. That's actually a faba bean plant earlier in autumn last year. They usually form colonies on growing tips, and that's the place where you should look for this aphid.

Cowpea aphid likes to form patchy colonies, and the best thing before you apply any management or spraying is to conduct monitoring in your paddock. The best way is to check at least five points in your paddock where you will inspect around 20 plants—so altogether 100 plants. After you find out about their numbers, since they have patchy distribution, then you will know how to apply economic thresholds.

Why do we need to spray this aphid in very low numbers? Because it's very well known as a vector of different viruses, including persistently transmitted and non-persistently transmitted viruses. If you haven't known the difference: persistently transmitted viruses are viruses for which it takes some time for an aphid to acquire and become infected, and after that, the virus stays in the aphid's body until the end of its life. On the other side, we have non-persistently transmitted viruses like cucumber mosaic virus, bean yellow mosaic virus, alfalfa mosaic virus, and pea-borne mosaic virus. Most of these viruses named here that cowpea aphid transmits are non-persistently transmitted viruses, and the main thing about that is that the aphids carry it for a few minutes up to a few hours in their body. The problem is that the aphid can transmit it immediately after feeding on an infected plant.

After you conduct monitoring, you should apply thresholds. According to this table here, it says that in lupins in New South Wales you should treat at the first sign of virus-infected plants or if you spot aphid clusters on flowering spikes. I would stay out of this first option because if you see a sign of any virus, it may be too late. So if you spot any aphids, then you should decide on management, like it says for faba beans in New South Wales: treat very low levels of aphids to prevent virus transmission. For chickpeas, there are no thresholds established.

Pea Aphid

The next aphid that I would like to talk about is pea aphid. Pea aphid is a minor pest of lucerne, for example, and an irregular pest of lucerne, but very often is found in pulse crops—also in faba beans, lupins, lentils, and chickpeas. You can see on this picture here, this is a chickpea. Pea aphid is not so often found in young chickpea crops, but later during the season it can be found if there is nothing more attractive for this aphid. It will stick on chickpea and survive for a very long period. It's enough if this aphid just stops by and feeds for a very short time because this aphid also can transmit non-persistently transmitted viruses like cucumber mosaic virus, bean yellow mosaic virus, alfalfa mosaic virus, and pea-borne mosaic virus. Also, this aphid is very well known as a vector of bean leaf roll virus, which is a persistently transmitted virus.

This aphid makes different damages on plants, including curling of leaves or wilting, and the plant can go stunted often. This aphid is common in spring but can be found during autumn or early winter. Again, you should do some scouting if you want to find out what you have in your field, and again inspect at least 20 plants at five sampling points and decide on the next step. If you want help about that, you can have here some economic threshold levels. For Western Australia, you should apply chemicals if you have more than 30% of growing tips infested, or according to New South Wales threshold, you should treat at the appearance of clusters of this aphid in flowering plants, or according to Victoria, if you have 10% of infested plants after you finish your monitoring.

Bluegreen Aphid

Bluegreen aphid is very well known as an aphid that can transmit different viruses and can be present in different crops, including pulses, but also in lucerne, pasture, and subclover. This aphid can also be found in canola, which is why we have developed an economic threshold for canola too. This aphid doesn’t come in big clusters—you won’t find it in big clusters like cowpea aphid or pea aphid—but it can still be present in big numbers in all these crops, including chickpea. It’s really rare to find bluegreen aphid in chickpea, but as you can see in this picture, we found it on a wild relative of chickpea (Cicer echinospermum) in really big colonies at our site here in Tamworth.

So be aware that all these aphids are capable of adapting to different conditions and different hosts. They can choose from a wide variety of hosts because most of them are polyphagous species. For bluegreen aphid, we have developed an economic threshold for canola in New South Wales: if more than 50% of plants are infested, you should apply chemicals. According to Western Australia, if more than 20% of plants are infested, you should treat. For lupins, you should treat at the first indication of virus-infected plants or first appearance of aphid clusters on flowering spikes. In Victoria, they say for faba beans that you should apply chemicals if you find 10% of plants being infested. For lucerne, if you find in your sweep net around 100 up to 400 aphids in five meters of sweeping. For chickpeas and lentils, there are no thresholds available at this stage.

Green Peach Aphid

Next is green peach aphid. Lizzie already said lots of things about green peach aphid, so I don’t want to repeat that, but it’s a highly polyphagous species that can attack different crops, including oilseed crops, lupins, pulses, and broadleaf weeds. That’s the biggest problem because this aphid has a very broad host range, including weeds like capeweed, marshmallow, wild radish, and wild turnip. All these weeds are host plants for this aphid, which makes our work around managing it more difficult.

This aphid is also very well known as a virus vector, so it can transmit different viruses including turnip yellows virus, turnip mosaic virus, cucumber mosaic virus, and pea-borne mosaic virus. So this aphid can transmit both non-persistently transmitted and persistently transmitted viruses. The biggest problem, as Lizzie already talked about, is that it has developed resistance to different chemicals, which adds additional pressure on us if we want to manage this aphid.

For this aphid, we don’t have an economic threshold developed, but that doesn’t stop you from going into the field and starting monitoring. This species can usually be found on the underside of leaves and doesn’t form clusters like pea aphid or cowpea aphid, but it can come in really high numbers if we do not manage it on time. So please, again, do scouting on time and look for it usually on the backside of leaves.

Faba Bean Aphid

The aphid I would like to mention here is one that’s pretty new for Australia and for faba bean growers: Megoura crassicauda, commonly called faba bean aphid. Cowpea aphid is found in Australia, but faba bean aphid was first detected in 2016 in a Sydney suburb. After that, in 2017, we found it in Tamworth in trials, and then in 2018 and 2019 during two drought years, when we had very few commercial faba bean crops, we couldn’t find it in those few crops in Liverpool Plains. We were hoping that this aphid didn’t establish in Australia, but that was not the case.

In July 2020, we found it in Grafton on faba beans. Later that same year, we found it in Liverpool Plains in northwest New South Wales, then again back in a Sydney suburb on a faba bean crop in Woolley Podwatch and also in gardens. There were also a few positives coming from the Mid-North Coast and central New South Wales. So apparently this aphid is pretty much spread across New South Wales, and there are some data that it’s present in Victoria too.

Faba Bean Aphid – Distribution and Identification

I don’t have official confirmation on this, but last month this aphid was found in Ipswich in Queensland. So obviously this aphid is pretty much established. The thing that you can do is look for it—if you find something suspicious looking like these aphids in the pictures, they are distinctive and easy to recognize. They have intense red eyes, a dark head, dark legs, dark powder, and dark siphunculi. So it’s pretty easy to distinguish. If you find something like that, make a picture and send it to me or anyone at Cesar. I know that Julia Severe was doing some identification with this aphid also, so whoever you want to contact, no problem—just let us know how far the distribution of this aphid is at this stage.

Distribution and Hosts

We’ve conducted some research on this aphid. It has a preference for faba beans in Australia, and also for vetches. We found it in faba beans, woolly-pod vetch, and it also likes common vetch, common pea, and lentils. Lucerne and subclover are alternative hosts—they support limited reproduction, but they can support reproduction for more than two weeks, which is enough for this aphid to make big colonies and start to spread. The biggest problem is that it can also transmit viruses. We did a study with a non-persistently transmitted virus (pea-borne mosaic virus) and a persistently transmitted virus (bean leafroll virus), and both viruses were successfully transmitted from faba beans to faba beans with the help of this aphid—unfortunately.

So keep monitoring your crop because this aphid, once established, can form really dense colonies. Usually, it’s found in patches and can infest all parts of plants—stems, leaves, even pods at the end of the season. The good thing is that this aphid is manageable. Pirimicarb works very well on this aphid, and all these outbreaks that happened, that I was talking about, we managed with pirimicarb. So good luck with that.

Symptoms of Virus Infection

Since I’m speaking about viruses, I’d like to point out some symptoms of different viruses in pulse crops and in canola—just to highlight what you should look for when you are in your paddock.

For example, turnip yellows virus on canola causes leaf distortion and comes with purple or reddish-yellow leaf discoloration. These are symptoms, and other symptoms can come together with these. Turnip yellows virus is a persistently transmitted virus, and the most important vector is green peach aphid.

Other viruses, for example, alfalfa mosaic virus and bean yellow mosaic virus, are non-persistently transmitted viruses. These two viruses were found quite often in faba beans last year. Alfalfa mosaic virus, like you can see on this picture with chickpea, often comes from lucerne, but lucerne doesn’t show any symptoms. In other pulses, you can find yellow mosaic developing or even necrosis in chickpea. Bean yellow mosaic virus is characterized by its yellowing—often with different yellow patterns, not only uniform yellowing. Bean leafroll virus, apart from yellowing, can cause upward leaf rolling, which is one of the most important symptoms.

All these symptoms can vary depending on season and host species. Even though on these pictures they look quite distinctive, it’s not always like that. That’s why I suggest all of you, if you spot something similar to these pictures, please send it to Tamworth or anywhere else. Here in Tamworth, Yaplan Lure and his team conduct analysis which will help you find out which virus you have in your crop. Why am I telling you this? Because, for example, in this picture you have bean leafroll virus, and here is soybean wilt virus, which looks very similar to the previous one, and then subterranean clover stunt virus. So they can expose similar symptoms. Just contact Yaplan Lure and pack samples adequately and send them to us for detailed identification.

Aphid Numbers

I’d like to follow up on numbers of aphids that we found last year and this year in pulse crops and canola in this region. Last year, we had quite high numbers of aphids in almost all of our sites. Numbers were coming up to 50 aphids per square meter. These numbers were quite high even for a normal year, and especially high compared to this year, 2021, when we had quite low numbers of aphids in our yellow sticky traps. You can see that the scale here is quite different—three times more last year. We found great numbers in 2020, especially in faba bean crops, but also in chickpea and lucerne, compared to 2021 when we had quite low numbers.

What we did find in 2020 were great numbers of pea aphid and cowpea aphid, which are known as good virus vectors, compared again with 2021 when we had pretty low numbers of these two aphids. In 2021, only in high numbers we found foxglove aphid in lucerne and canola, and foxglove aphid is known as a very poor virus vector.

Virus Outbreaks: 2020 vs 2021

In 2020, we had a big number of positive examples and significant outbreaks, especially west of Moree, with faba bean samples being infected with bean yellow mosaic virus and alfalfa mosaic virus—both non-persistently transmitted viruses—and low numbers of bean leafroll virus. Comparing to 2021, we had almost no positives in our samples collected from the same area—very low numbers of positive examples in 2021.

Why Did This Happen?

In 2020, after two years of drought, January and February rains in northwest New South Wales triggered the emergence of pasture legumes, which were really good hosts for aphids to start multiplying. These legumes provided a great source for aphids, and with full soil profiles, we sowed faba beans very early in the season, which was a great opportunity for aphids to move early into faba beans and cause problems in establishing crops. As part of that, we had these kinds of problems in paddocks, especially west of Moree, and these infections became a source for later crops like chickpeas. These infections were spread across the whole year. The first part of the year was very favorable for aphids to multiply—mild conditions supported aphid survival and virus transmission across the season.

On the contrary, in 2021, we had very cold and wet conditions. Autumn was cool and wet, and even though we had full soil profiles and early-sown crops, we didn’t have perfect conditions for aphids to establish in crops because we had cool days and nights and early frosts in April. All these conditions affected aphids, and they didn’t manage to transmit viruses. We sampled aphids around paddocks and inside paddocks and found very low numbers. We conducted TBIA tests and found very low virus presence. That’s a really good result because crops looked great and yields were strong. Healthy crops are more likely to resist virus infections, which was an additional advantage for us.

Virus Control Measures

At the end, I’d like to repeat some virus control measures already mentioned before. There is no option to control viruses directly—only preventive measures can be done. So we should think about that:

• Control weeds and volunteer crops on time.
• Avoid sowing close to inoculum sources like lucerne paddocks or near volunteer plants.
• Use high-quality seed.
• Use resistant varieties if available. Breeding for turnip yellows resistance in canola and pulses is underway, but there are no resistant varieties yet.
• Sow canola and pulse crops in cereal stubble to limit colonization. Retaining stubble can reduce aphid landing rates according to WA results because bare ground attracts aphids more than retained stubble.
• Rotate canola and pulses.
• Sow early to establish canopy closure—this shades out weeds that could be virus sources.
• Remove virus-infected plants where possible.
• Crop monitoring—constantly monitor and, after establishing representative numbers, apply insecticide.

Seed Treatment

We conducted research on imidacloprid seed treatment in glasshouse studies. It was not effective on the first day, but was quite good and effective on the third, seventh, and fourteenth days of observation. Seed treatment can be ineffective for non-persistently transmitted viruses because these viruses are transmitted immediately after aphids feed on infected plants. So there is no option to stop aphids from transmitting non-persistent viruses, but you can slow down their colonization in your paddock.

Natural Enemies

Finally, pay attention to natural enemies of aphids in your paddock—hoverflies, lacewings, lady beetles, and other beneficials. They are very important for balancing pest populations and reducing the need for insecticides.

Thank you from me, Lizzie, and all others.

Hand Lenses

Thanks very much, Zaritsa—that was wonderful and really good coverage of some of the issues you face in New South Wales with aphids in your local areas. One final thing: Liz did manage to send out some hand lenses to those of you who provided your addresses. If you haven’t received one already, Liz has given you her details—you can get in touch with her. I think she’ll send them out to everybody who registered, is that right Liz? Yes—only people that provided details and were interested. Fantastic. Those lenses are a great tool, especially when you’re looking at tiny insects like aphids. We’d love to see a photo of you using it! If you’ve got a photo taken with your hand lens or a photo of you using the hand lens, please send it over to Liz. She loves insect photos and seeing people taking photos of insects, and we hope this encourages you to keep monitoring.

Wrap-Up and Questions

Get out into the field and do some aphid identification as well! We do have a quick minute for questions if anybody's got a burning question. Otherwise, if you have aphids you would like to send to us, please do get in touch with me because they're very valuable to our research. You're also welcome to get in contact with us using the contact sheet that Liz will send around to you.

We'll send a copy of the recording and all the links that have been mentioned in the presentation today.

Okay, I didn’t see anything written in the chat, so thanks very much for coming today and we'll see you next time—hopefully. Thanks, bye!