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.
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
…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.
resembling an enigma, or a puzzlingoccurrence,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.
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:
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.
2. Lamb, R. J., W. J. Turnock, and H. N. Hayhoe. 1985. Winter survival and outbreaks of bertha armyworm, Mamestra configurata on canola. Can.Entomol. 117: 727-736.
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 are probably 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
If you’ve followed this blog, you may know I have a penchant for word play and grammar jokes. So yes, here’s another one:
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 in western Oregon for over 40 years.
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:
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/>
AUGUST 2018 – EDITS to the original (FEB 2018) post
Ok, now that I’ve got your attention…
The subject line is a playful way to introduce you to Apamea devastator, although the damage it can do is no laughing matter.
This species overwinters as mature larvae, and I found some south of Corvallis just last week.
Larvae live underground, and feed on roots and the base of plant stems.
Host plants include:
Grass (pasture and seed)
In outbreak years, feeding has been reported on: cabbage, lettuce, bean, beets, and radish
This pest is particularly fond of fescue, timothy, and bluegrass. Outbreaks have occurred in PNW fescue.
SCOUT IN SEPTEMBER AND OCTOBER by surveying grass fields for any sign of browning-off or slow growth. In herbaceous plants, the first sign of injury is often WILTING. Dig up the roots and search surrounding soil for translucent, large (3cm), greenish to white larvae with little to no body markings, except for the brown prothoracic shield just behind the head. Common name: glassy cutworm refers to the light, almost ‘glassy’ appearance, versus most other cutworms that have distinctive markings along the surface of the body (examples here).
It is important to realize that general predators can keep cutworms populations suppressed below damaging levels. Parasitoid pressure, however, may not be as effective for this species; a 1990 study from Oregon found that the cutworms matured almost to pupation before they were killed by parasitoids, thus feeding in the current season is not suppressed. Try to consider the impact on natural enemies before choosing to apply chemical controls.
If scouting reveals a need to make a treatment, consult the PNW Insect Management Handbook, and be sure your crop is listed on the pesticide label. Rain or irrigation may help move the product into the soil surface, which is important for this species.
TIPS FROM THE FIELD/LITERATURE:
This year (2018), I am catching A. devastator adult moths as non-targets in traps placed near cole crops. This could mean they are emerging from fields where they did early-season damage as larvae – because they feed on roots and stems, perhaps this is one of the factors contributing to the broccoli mystery. It also suggests that actual population numbers are higher than normal, because I usually do not see this species in my traps.
In fine fescue, damage from larvae tends to occur more on plants that are within 3 ft of a weedy grass.
A. devastator has dangerous similarities to Noctua pronuba, the winter cutworm: both species have erratic outbreaks, and have caused damage to Oregon crops in previous years. Both overwinter as larvae, and have been documented feeding throughout the fall and winter. (E.G. THIS ORIGINAL POST – FEB 8th, 2018)