…Could be the name of a Halloween party cover band, don’t you think? But in fact, these are the common names for Pyraloidea adults and larvae, respectively. Pyraloidea is the third largest superfamily of the Lepidoptera, and is comprised of two families – Pyralidae and Crambidae. Together, there are about 16K species worldwide.

Within the group, there is incredible diversity of feeding habits. Larvae feed on corn, rice, and other grains and grasses, ferns, fruit and vegetable crops, potted tree seedlings, and even excretions of sloths and bats. Some species have larvae that are fully aquatic – very rare indeed for a baby moth or butterfly! Common names “CRANBERRY GIRDLER” and “GRASS-VENEER MOTH” also reflect feeding behavior.

Adults are called ‘snout-moths’ because of the long, upturned labial palps on the mouth region of the head (FIGs. 1 and 2).

anatomical sketch
FIGURE 1. Head anatomy of Pyraloidea. ILLUSTRATION BASED ON: GF Hampson 1892. Fauna of British India. Public domain {{PD-US-expired}}
FIGURE 2 – Adults cranberry girdler with eggs. PHOTO CREDIT: CD Barrentine, bugguide.net
IDENTIFICATION

Adult snout moths are slender and hold their wings folded over their back when at rest. Wing patterns vary by species. These moths fly low and usually in a zig-zag pattern; this habit can be useful when scouting.

Larvae are slender, white to cream-colored caterpillars with tan heads. They have 3 thoracic (true) prolegs and 5 abdominal prolegs and can therefore be confused for cutworms (earning them a spot on my blog here!). Figure 3 shows identifying characters of webworms. The comparative ID guide for cutworms can be viewed here.

Larvae vary in color from black to green to tan depending on food source, species, and age. Raised, sclerotized areas of the integument look like brown ‘spots’ along the body. The spots become more prominent with age but be careful: cranberry girdler’s spots are the same color as the integument and therefore not obvious. Mature larvae range from 5/8 to 3/4 inch long.

FIGURE 3 – Webworms can look very much like cutworms. Both have 2 setae (hairs) on the lateral side of the prothorax, but one must examine the orientation of the crochets to tell the difference. In Noctuidae (cutworms and armyworms), the crochets are arranged in a row or half-circle.
DAMAGE & MONITORING

Cranberry girdler is more difficult to detect and control than other, related sod webworms because it typically feeds at or below the thatch layer. This species is sometimes called ‘subterranean webworm’. Digging and sifting through soil is one way to detect the presence of larval webworms, but if an infestation is suspected, the most effective way to confirm it is to pour 2 gallons of a soap solution over an area of about 1 square yard. This irritates the larvae and causes them them to come to the surface. 5 webworms per square yard is considered to be an action threshold in most grasses.

TREATMENT

Sod webworm seems to thrive in drought conditions, so regular watering can help reduce the risk. Various products are registered, consult the PNW Insect Management Handbook for suggestions. Mid-summer is the best time to apply treatments, because larvae overwinter deep in the soil column and therefore are harder to reach in fall and spring.

Please take note that the 2nd flight of Mamestra configurata is much higher than normal. Larvae of this species exhibit armyworm behavior – larvae move and feed in groups. Visually scan fields for areas of defoliation or seedpod feeding, and search surrounding soil – or flag the location and return at night.

Damage can be extensive on a number of economically important Oregon crops including: MINT, ALFALFA, BELL PEPPERS, CORN, VEGETABLE BRASSICAS, and CANOLA.

Pay special attention to weedy fields – lambsquarters and pigweed are often used as egg-laying hosts.

Outbreaks of this species are rare, but can occur every 6-10 years. The 2010 Willamette Valley outbreak had 2 distinct peaks of very high activity compared to the long term average(grey shaded). Damage from this 2nd generation can occur into early autumn.

Adult moths have prominent white reniform spots (‘kidney bean-shaped’) and an irregular thick, white band near the terminal edge of the wing. There are 2 distinct generations per year, and adults can fly up to 50 miles from where they originated.

Identifying larvae is difficult in because there are different color forms that can vary substantially. Usually present is a yellow-orange line separating the ventral (pale) and dorsal (darker) areas, and the head is tan or light brown.

  • Scouting recommendations and more info: related blog post, 2018
  • New publication on dispersal patterns and source populations in W. Canada: Erlandson, M., et al. (2019). “Examining population structure of a bertha armyworm, Mamestra configurata (Lepidoptera: Noctuidae), outbreak in western North America: Implications for gene flow and dispersal.” PloS one 14: e0218993.
  • PNW Handbook

Original content is great, but sometimes it is unnecessary to reinvent the wheel, or in this case, the YouTube video about armyworm damage in wheat.

We are starting to monitor true armyworm (Mythimna unipuncta) in the PNW, but efforts from Midwest states are much more deliberate because the species can be so damaging to large acreage of grasses and grains.

Today I found this excellent video from Chris DiFonzo at Michigan State University. Chris explains damage to flag leaves, thresholds and how to scout for larvae, and predicted impact on yield. Grab a cup of coffee and watch the 8-minute video here: https://youtu.be/C-Pk0ANkDr4

Cover image of YouTube video

Soil type and the parameters associated with it (water holding capacity, %OM, etc.) could be important as we continue to investigate armyworm population dynamics. The Web Soil Survey is a useful, interactive tool that is freely available to all.

Investigating soil properties at field level may reveal trends important for pest management.
  • We are trying to discern why certain sites in our Tillamook trapping effort have 10-20X the amount of armyworm moths detected.
  • We know that when there is abundant soil moisture, more eggs are laid, and more eggs hatch, which increases the risk for damage by larvae.
  • Sites less than 5 miles apart have similar pasture management but very different trap counts.
  • In low-lying areas like coastal Oregon, the distance to the water table might vary between fields

I encourage you to check out the Web Soil Survey tool (link above) and do some “digging” around – there’s a wealth of information available!

Predicting cutworm and armyworm pressure is difficult. But without predictive tools (monitoring of adult moths, crop scouting, and detection of larvae), cutworm and armyworm attacks are only noticed too late, when the most severe damage has already been done.

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

 

.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!

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.

Rapid spread across continents is a global concern. Credit: Roger Day, CABI Action on Invasives council

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.

S. frugiperda has a series of offset black spots on its back and 4 large spots at its posterior end. Photo credit: Feed the Future Innovation Lab, Virginia Tech.

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.

 

 

References
  • 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

 

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.