Here are some factors that affect activity levels:
- Cyclic booms and busts of pest population levels affect the balance of natural enemy regulation, which is one reason why we seem to have ‘bad’ cutworm and armyworm (and looper!) years followed by years where populations seem more normalized.
- Some of the cutworm and armyworms we have in this region arrive each year as long-range migrants from southern latitudes. Weather patterns such as el Niño and la Niña can affect migration patterns.
- Another predictor of risk is winter moisture level, both locally and in areas where moths overwinter. These, and other abiotic factors contribute to cutworm and armyworm survival and potential damage each year.
Wet Winter = Worms
Okay, so the equation isn’t quite that simple, but we do know that armyworm outbreaks tend to be worse after years with excessive rainfall from Sept-March. Due to recent trends, we will be researching WHY outbreaks happen and if we can better predict them. Stay tuned… (and tell your friends to subscribe for updates!).
Armyworm species, in particular, exhibit moisture dependency. This simply means that the percentage of egg hatch is greater if there is abundant soil moisture. Our regional precipitation was relatively normal from January-March (below, left), but 200% wetter than normal in April (right), and the flooding in May could affect egg hatch as well.
Maps courtesy PRISM program, Oregon State University white=normal; yellow=slightly less; green=approx. 2X increase
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!
Africa looks to biocontrol to reduce fall armyworm problems
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.
Bateman, ML, Day, RK, Luke, B, Edgington, S, Kuhlmann, U, Cock, MJW, ‘Assessment of potential biopesticide options for managing fall armyworm (Spodoptera frugiperda) in Africa,’ J Appl Entomol. 2018;00:1–15.
Virginia Tech Feed the future innovation lab video
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.
So yes, insects have joined the ranks of migratory songbirds, salmon, sea turtles, and probably many other organisms that use geomagnetic signals to navigate.
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
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 **.
- resembling an enigma, or a puzzling occurrence, situation, etc.; perplexing; mysterious.
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.
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!
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:
- Fruit trees
- Weeds: especially lambsquarters, Canada thistle, and sow-thistle
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].
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.