.pdf is NOW AVAILABLE for download .
The full version of:
“ARMYWORMS AND CUTWORMS IN OREGON CROPS:
A comprehensive guide to identification, ecology, and management of common species”
is expected to be published early summer, and will include more species, as well as notes on scouting, host plants, activity in the landscape, etc.
This is a huge group to try and summarize, so if you have thoughts or questions about certain species, feel free to leave a comment!
Fall armyworm (Spodoptera frugiperda) has been a devastating pest of cereal crops in Africa since 2016, when it was introduced from the Americas. It has since spread to over 20 countries in sub-Saharan Africa. Just this year, it was found in India as well.
Fall armyworm is particularly dangerous because it has a wider host preference than related species (it feeds on 150+ plants including rice, sugarcane, legumes, and cereal crops). Grains like corn, sorghum, and millet are not only a food staple for hundreds of millions of people, they are the root of other commodities like forage and biofuels.
Pests, drought, and extreme poverty already afflict many farmers, and there are both knowledge and income gaps that prevent wide use of pesticides or other control tactics.
Enter: the good news.
Tiny, tiny wasps.
We know that beneficial parasitoid wasps help regulate cutworm and armyworm populations, but on their own, they cannot help in an outbreak situation because there are simply not enough of them to make an impact. Unless – their numbers could be exponentially increased for very little money and people could be trained to ‘raise’ them.
One tiny wasp, in particular, Telenomus remus, already exists in the region, is easy to rear, and is not deterred by the ‘hairy’ covering that protects fall armyworm egg masses. Even better news: the technique of raising the wasps is being taught to local farmers so that the strategy can be implemented large-scale.
Scientists have been able to implement a mass-rearing program to enhance native natural enemies that attack fall armyworm eggs and larvae.
Fun fact: Some of our own Beaver emeriti (P. Jepson, D. McGrath) are working towards developing solutions to the fall armyworm crisis in Africa.
Regional trapping of true armyworm (M. unipuncta) in Tillamook county has been ongoing since May. Only 6 of the 15 original monitoring sites remain, but at those sites, we have seen a sharp increase in trap counts.
We know that it is normal for armyworm to have 3 generations per year, which matches the pattern we see here:
This is our first year trapping this species, so these data are invaluable – thanks, Tom!!
Although the traps are in NW Coastal Oregon, it is not unreasonable to assume that activity patterns are similar here in the Valley. More importantly: This recent peak in adult moth trap catches suggests that (larval) armyworm activity THIS FALL is likely.
If there are any grass seed growers out there who haven’t sprayed yet (which I doubt there are), you may want to consider it. Product list here. Or at least hop on the four-wheeler and have a scout around. And remember that insecticides work better on smaller larvae, and by time you see apparent/massive damage, it may be too late for controls to be effective.
A few months ago, a paper was published, confirming that Bogong moths (Agrotis infusa) use geomagnetic fields as a navigational tool for their en-masse aestivation flight.
Say what, now?
Long-range migrations are common in the insect world, the most ‘notable’ (as in..the one in which most people take an interest) is that of the monarch butterfly. The migrations occur each year, are purposeful, and serve some ecological function; to reach breeding sites, etc..
In the case of the Bogong moth, millions of moths leave the plains of Australia and fly towards the high country of the Victorian alps to escape the heat and avoid desiccation. They congregate in such large numbers in the mountainous habitat that indigenous peoples would go there to collect the moths as a food source. They are also a preferred staple for mountain pygmy possums. In autumn, the moths return to the plains to lay eggs and the cycle begins again.
Aestivation is just a fancy word for: reduced state of biological activity that occurs in response to hot and dry conditions. It is a sort of ‘summer hibernation’, if you will.
Closer to home, we have Euxoa auxiliaris that exhibits the same pattern (replace pygmy possums with grizzly bears and Australian Alps with Rocky Mountains). The study found that successful orientation relies on a combination of visual cues and magnetic frequencies emitted by the earth, and that when either cue was missing or altered, their flights became uncoordinated and erratic.
Many other creatures exhibit magnetoreception (using geomagnetic signals to navigate): migratory songbirds, salmon, sea turtles, and others. 2021 update: leaf-cutter ants
Now we just someone to develop the superhero series for these Persistent, Amazing, Perceptive, and Strong …mutants?
No, wait – that name’s already taken:
Author note: not sure why the Dreyer et al. is being referred to as the ‘first’ discovery – 1. Baker, R.R. and J.G. Mather, Magnetic compass sense in the large yellow underwing moth, Noctua pronuba L. Animal Behaviour, 1982. 30(2): p. 543-548.
Other note: concerns of pesticide distribution, bioaccumulation and toxicity levels in this type of system have been raised since at least 2006, and warrant further review, IMO
…Over the past 2 weeks, I have started to detect Noctua pronuba in pheromone traps. There is a commercial lure available, and I have some of those deployed currently, but honestly, have just as good of luck tracking them as non-targets in other armyworm traps.
In 2017, there were 2 apparent activity periods, which matches with published estimates from U. of Idaho, one of the only other places in the country with a documented outbreak of winter cutworm. Click here to see an interactive comparison of trap catches between years, so far.
Keep in mind, these observations are NOT, at this time, part of a full-fledged sampling program for Noctua pronuba. Rather, I am mentioning adult flight because it is an indicator that there is POTENTIAL for winter cutworm activity starting about September 10th.
** Please review the OSU Extension publication for more info about host plants, history, biology, and identification of this species **.
Enigmatic:
Euxoa:
genus of moth, with over 120 species in the PNW, characterized by extreme difficulty in identification due to polymorphism, sexual dimorphism, and wide variation between individuals.
Identifying Euxoa moths by external morphology is extremely difficult. Forewing shape can provide a clue, as can vein and fringe color of the hindwing, but beyond that, one is left with an almost insurmountable challenge. In fact, true species ID can only be accomplished by genitalia dissection and/or PCR.
Some of the known crop pests we have in Oregon include:
E. ochrogaster, the red-backed cutworm
E. auxiliaris, army cutworm
E. messoria, darksided cutworm
Other species, including E. punctigera and E. vetusta are quite common here, according to sighting records, but no one has any idea what the larval foodplants may be, or if they behave differently than related species.
I am currently building an identification key to some of our most common cutworms and armyworms. There is a preview here, and as always, feel free to contact me if you have specific questions.
Regional trapping in Tillamook county has been ongoing for 6 weeks. We’ve recently begun to incorporate GIS maps to make it easier for program leaders and participants to visualize ‘hot-spots’ of armyworm moth activity.
Of 15 total monitoring sites, positive trap counts this week are confined to a 5 mi2 area, centralized around Tillamook city limits. This type of pattern can only be visualized by mapping, and may help focus efforts for further scouting. Fun stuff!
As we endure the College World Series rain delay, let’s take time to learn about a different type of strike. (A segue stretch, I know)…
Mamestra configurata Walker, bertha armyworm, is native to North America and is a major pest of canola, so most published literature reports on damage and economic thresholds in Brassica rapa and B. napus, and some suggest that populations (in Canada) have gotten worse with the increasing acreage of rapeseed1.
This species has been monitored for 20+ years via the VegNet program, and outbreaks in vegetable crops have been few and far between. However, as with any armyworm, scouting is KEY because when damage does occur, it happens quickly and usually on a large scale.
Larvae feed above-ground, on foliage and fruit of hosts from over 40 different families. Some of the documented hosts include:
After group feeding on foliage as ‘baby’ caterpillars, mid-stage larvae spin silk threads that help disperse them on the wind, a few meters within a field, and voracious feeding begins.
SCOUTING for bertha armyworm involves leaf pulling and visual scans. As a scout crosses a field pulling and examining leaves, they should stop every ten leaves and scan for a plant or a small grouping of plants with a lot of holes in the leaves, then walk to that location and try to find larvae.
These patchy, hard-to-find areas of damage are called armyworm “strikes” [there it is].
MANAGEMENT
Natural enemies (predators, parasitoids, viruses) probably exert heavy levels of control on bertha armyworm, otherwise we would see more frequent outbreaks.
1. Dosdall, L.M. and B.J. Ulmer. 2004. Feeding, development, and oviposition of bertha armyworm on different host plant species. Environ. Ent. 33(3): p. 756-764.
Apamea cutworms can be serious pests of grasses. There are a few different species that are common in this region. Two of them have fun common names.
A. cogitata, the thoughtful Apamea
and its more unfortunate contrary:
A. dubitans, the doubtful Apamea
The current activity of this common group of moths is not of direct concern. Rather, it is the active, overwintering larvae that are considered pests because they feed on grass roots. A. dubitans and A. cogitata could be similar to the congeneric A. devastator, which only has 1 generation per year. I made a post about them in February.
In western Oregon, glassy cutworm (Apamea devastator) moths emerge in late June, peak in July, and larvae take 100-120 days to develop, depending on daylength1. The species we caught in traps this week (thoughtful and doubtful) are less well-studied. But I wager a guess that we could begin to see larvae in fields by about mid-September.
Fun fact: “cogitare” translates from Latin as “to think”. One of Francis Bacon’s most famous works “Cogitata et visa” (“Thoughts and Conclusions”) was written in 1612. In it, he posed that philosophy and science have common interests.
1 Kamm, 1990. Biological observations of glassy cutworm in western Oregon. Pan-Pac.Ent. vol. 66
Black and Bluhm – in reference to Agrotis ipsilon (black cutworm) migration patterns and Wilbur L. Bluhm, Emeritus OSU Extension agent who tracked the phenology of many ornamental plants for over 40 years. His dataset is specific to the mid-Willamette Valley.
Phenology is the study of periodic life cycle events and how they change from year to year. It is an armchair hobby of mine, and also has direct implications for crop pest monitoring. Plants and animals alike develop and progress through life cycle events (leaf out, molting, bud break, etc.) according to temperature.
When Spring arrives 20 days earlier than normal, the implications become even more important. In the animation below, red represents “spring leaf index” occurring earlier than normal and blue indicates later.
Black cutworm, like many crop pests, exhibits long-range migration behavior, and adult moths depend on nectar sources to literally fuel their journeys. A recent study1 examined pollen load on A. ipsilon antennae and found that they are especially frequent visitors to flowering woody dicots like honeysuckle, hawthorn, hazelnut, alder, oak, maple, etc.
According to Bluhm’s tracking2 , most of the plant species mentioned above are, in general, blooming earlier than they used to here in Oregon. This obviously varies widely by year and by species, but bear with me…
If more floral resources are available, earlier, and insect development also is ‘ahead of schedule’, it stands to reason that moth flights could be affected.
The chart below shows peak flowering of three common woody species, and their phenology over the past few decades. I compared this to my dataset of black cutworm moth trap counts and found an interesting pattern:
And now, just for fun..listen to this and ponder the potential relationship between black and bl[oom] !
1 Liu, Y., et al. 2016. Host Plants Identification for Adult Agrotis ipsilon, a Long-Distance Migratory Insect. Int’l. J. Mol. Sci.,17(6).
2 The Wilbur L. Bluhm Plant Phenology Study <http://agsci-labs.oregonstate.edu/plantphenology/>