(00:00): Thanks [Leonie 00:00:01] and thanks everybody
for joining us for this webinar this afternoon. Basically, I want to go through a little bit
about the biology of fall armyworm, distribution, why it's suddenly become an issue here in
Australia when it hasn't been previously, a little bit about the host plants, and also
the damage that fall armyworm can cause.
(00:22): The fall armyworm is quite typical of other
[inaudible 00:00:26] moths. It's very much a similar life cycle. As with all insects,
the duration of the life cycle for fall armyworm is very temperature dependent. The hotter
it is, within reason, the faster it develops. Typically, the developmental period from egg
through to adult will be between 24 and 55 days. The mature larvae get up to about 35
millimetres in size. The female fall armyworm moth can lay up to a thousand eggs during
its lifetime, usually in batches of 50 to 100. Those eggs will ultimately hatch and
there will be six larval stages. Those larval stages get progressively bigger in size, and
of course it's the larval stage that does the damage to the crops. The larvae ultimately
pupate and in most cases, the pupae will be in the soil. In some cases, with crops such
as maize, you can get pupation actually within the maize cobs, and some growers will be familiar
with that from heliothis. A similar thing occurs there.
(01:30): Now the big, and perhaps one of the saving
graces for us in most of New South Wales anyway, is that fall armyworm is a tropical to subtropical
species. It can only survive relatively mild winters. If you have a really good, cold winter,
you will not get any survival. And that's largely because the pupae cannot enter into
a diapause in the soil in response to low temperatures. So typically a tropical to subtropical
pest and as a consequence, it's probably going to cause a lot more problems in Queensland
and the Northern Territory and the northern part of western Australia than it will in
New South Wales. But we do have to be alert and I'll explain why.
(02:13): This is a little bit about the spread of fall
armyworm. Fall armyworm is a native insect in the southern parts of the United States,
Central America through Mexico, and down into South America as far as Argentina. It was
confined to those areas for a long period of time, and in 2016 it turned up in West
Africa. I haven't heard a compelling argument as to how it got there, but it certainly did.
And as it spread through southern Africa it caused tremendous problems, particularly for
subsistence maize growers. Maize is one of the most vulnerable crops to fall armyworm.
So it was causing a lot of grief there and it moved across Africa quite rapidly. It turned
up in India in 2018 and it wasn't long before it had spread further east into most of southeast
Asia across 2018, 2019.
(03:09): This particular graphic is a little bit out
of date in that it doesn't show the movement down into Australia. It turned up here fairly
recently. It moved across the Torres Strait, or at least that was our first detections
of it. It is now found in the top of western Australia. It's also known from the Northern
Territory. And in Queensland, it's now known from as far south as Bundaberg and that was
mid-April progress.
(03:34): This is one of several modelling exercises
that has predicted the spread of fall armyworm. This one shows South American, southern part
of the USA, which is the native host of native distribution of fall armyworm. As you move
across into Africa you can see that the darker the colours, the more suitable the area is
as a habitat for fall armyworm. So basically, the central areas of Africa are the most vulnerable
except for high altitudes. You get across into southeast Asia and it's places like Vietnam,
Cambodia, that you can see there with the darkest coloration that are the most susceptible
or most vulnerable, providing the best habitats for the insect.
(04:19): In this particular map, when you get down
to Australia you can see that the darkest areas are on the Queensland coastal area,
southern to mid-Queensland, and to some extent northern Queensland, and also over in the
odd area. There's small areas of darker coloration on the map in the south of western Australia
as well. One thing here, it shows that a lot of New South Wales appears to be in that grey
coloration which says not suitable. Now this is a model that's used as a particular set
of data and assumptions, and there are considerably more developed models around.
(04:56): And this is probably the best one that we
have. This is from CSIRO. I use the CSIRO software known as CLIMEX, and it takes into
account all sorts of different variables as well as climate. Where you can see the white
areas in the middle of Australia, there's believed to be no population growth of fall
armyworm will occur in those areas. A combination of climate and also availability of food plants
and sufficient moisture and so on. If we go next to the pink areas, that's where fall
armyworm could appear as a response of migratory movements, but you wouldn't get a full generation
there. Essentially the herd accumulations across spring and summer are not enough for
a full generation of fall armyworm to get through to adulthood.
(05:48): Next up is the green areas. And these are
areas, and you can see a lot of New South Wales, with the exception of the far north
coast, is pretty much in this green category. Now what that means is that you can have migratory
movements of moths into this area. You could have one or more complete generations of moths
over the warmer periods. Once again, they will not survive in winter.
(06:11): As you go up into yellow, orange, and then
red, as you move further north and up into Queensland, these habitats become progressively
more suitable. And anything from yellow upwards suggests that the moth could maintain populations
there year-round. They will not die out during winter. So in New South Wales, that's really
the far northeast corner. So in a lot of the cropping areas in the inland parts of New
South Wales, we're vulnerable to fall armyworm based on the current models, but that will
come about through the migration and movement of adult moths from that northeastern area
or southeastern Queensland where the moths can persist all year.
(06:57): So in one respect we're fortunate in that
in a lot of New South Wales, the moths cannot maintain a presence throughout the entire
year because of the colder winters. On the down side, however, fall armyworm adults are
particularly strong fliers. They've moved with what appears to be fairly astonishing
speed from Cape York down as far as Bundaberg in a matter of a couple of months. And the
adults are known to fly up to 100 kilometres overnight and over 1000 kilometres during
their lifetime. So we are vulnerable to these migratory movements of moths during spring
from areas where they have persisted over winter.
(07:38): One feature of more localised dispersal that
you get with fall armyworm is the ballooning, if you like, of first instar larvae. So when
the eggs hatch and produce these larvae, you can see on the right hand photograph there,
they will come down on a silken filament and that will detach from the plant and they will
basically be blown around randomly on the wind in much the same way as some young spiders
that you see move around as well. So those movements are totally random and short range,
as opposed to the adult moths which can cover a lot of ground.
(08:19): So in terms of the number of host plants that
are affected, looking at cropping plants here there's over 80 plants recorded. So it's quite
a large range of plants. If we look at non crop plants as well, I think the total is
in the order of about 350 different plant species that fall armyworm will feed on. But
far and away, the worst damage to crops involve grass-based crops. So things like maize, sorghum
wheat, barley, rice, oats, sugarcane, all very potentially very badly affected. Other
crops like soybeans, lucerne and clover pastures can be affected as well. The only vegetable,
well amongst all our vegetables we feed on, it's only regarded as a really serious pest
of sweet corn in the vegetable area. Cotton is a host of fall armyworm, but of course
most of the cotton we produce in Australia now is BT transgenic cotton. It has a defence
against heliothis and the fact that it's BT transgenic means it's unlikely to be significantly
damaged by fall armyworm, though any refuge area crops, for resistance management that
involve non-BT cotton are likely to be affected by fall armyworm.
(09:38): There are a couple of different biotypes of
fall armyworm that are known to occur. And the minute, the judges are still out on which
variety or which biotype we have here in Australia. They do hybridise, so it's not a very simple
question to answer at this point.
(10:01): There's, as I said, a very large number of
crops that are affected by fall armyworm and it's not within the scope of today's webinar
to go through and talk about the specific sorts of damage to more than a couple of crops.
So in this presentation, I'm just going to show a few pictures of the damage that occurs
to maize and sweet corn damage is pretty much identical, and also damage to rice. As these
are two of the very significant crops most severely affected.
(10:29): If you look at the top left picture here with
the damage to maize, you can see newly hatched first instar, possibly second instar larvae.
And they're grazing away on the surface of the maize leaf and they're creating this sort
of windowing effect as they remove the top layer of the leaf tissue. They're not actually
mining below the epidermis of the leaf, they're grazing across the top of it.
(10:50): The picture at the bottom left shows a very
heavily affected maize plant. The crown is shown there, or what's left of it, and you
can see that a lot of the leaves surrounding it have been either shot holed or had the
edges grazed on by the larvae. You can actually see a lot of frass, or droppings from the
caterpillars, particularly on that leaf on the right in that picture.
(11:16): The central picture is the mature fall armyworm
larvae, showing the sort of shot hole damage it produces in maize leaves. And on the right
we've got a couple of the larvae that are burrowing into the cob in a very similar style
to heliothis.
(11:29): And here's an indication of what they can
do to rice crops as well. This is in the southern part of the United States. The shot on the
left shows the typical sort of damage with sawtooth cuts on the end of the rice leaves
or sections taken out on one side of the midrib. The central picture is a crop that's been
flooded, and that gives you some idea of the sort of densities of larvae that you can get
on individual plants if there's a heavy infestation in a crop like rice. On the right, we've got
a crop that's either being drained or it's between flushes in an irrigated situation.
When you don't have any water on the crop, you can actually get very large groups of
armyworm moving from pastures and so on into crops like rice and producing this very severe
damage along the edge of the crop.
(12:33): As for control of fall armyworm, in a lot
of countries where fall armyworm is present and particularly in its native range, predators
and parasitoids can be very effective for providing control, provided that they're conserved
by minimising the use of the broader spectrum insecticides like pyrethroids and so on. Just
how effective are native Australian beneficial species for fall armyworm control is not yet
known. Certainly with our other armyworm species that we have in Australia, things like common
armyworm and so on, we do get very high levels of parasitism and quite significant levels
of predation. But whether our native beneficial insects can adapt to feeding on fall armyworm
is really something that we're only going to find out with a bit of time. Until we know
a bit more about fall armyworm and what sort of damage it is causing to our crops and the
level of natural control that we can achieve, insecticides are going to play a very significant
role for fall armyworm control in Australia.
(13:42): The key to using insecticides effectively,
and Janine will be talking about permits and so on later on, is regular crop monitoring.
Our populations of armyworm, whether they're fall armyworm or whether they're some other
species, one of our native species perhaps, they can build up very quickly before growers
are aware of the population levels that are developing, particularly in hot weather. And
they can do a lot of damage very swiftly. So regular crop monitoring is very important.
Another aspect of crop monitoring is that in general with most of these caterpillars
and fall armyworm, if you can spray when the caterpillars are smaller, any chemical spray
is most likely to be more effective at that time. The larger the caterpillars, the greater
the tolerance to insecticide doses, generally speaking.
(14:32): I would just like to at this point give some
credit here to a lot of the organisations whose material we have used in these presentations.
Thank you.