9-15-18 A soon-to-be customer reported he’s been finding about 50 mealworms a day entering his house. One crawled all the way into his ear canal while he was sleeping. He removed it with his pinky finger. Jamestown area.
We received an email about what appears to be an outbreak of Eurasian mealworms in Elverta, in Sacramento County, California.
Cindy, the homeowner, sent photos, posted below, and said “For the last two summers now we have them falling from any ceiling opening into our house! They drop down from the attic from any light fixture and sprinkler heads. They are also all around the exterior of our house.” Cindy also observed: “They do seem to be worse on the back patio where we have a porch light so I do think they are attracted to light. When they land on our floors they find something to hide under. So they will gather under our rugs and floor mats.” At this Elverta location, the home is a manufactured house, and there is no accessible attic.
Her observations match what we have heard from Sheri and Lori, in the Sonora area, that the larvae appear to be attracted to lights, and that the larvae hide under things like rugs and mats. At Sheri’s house, in Tuolumne County, you could find the larvae under artificial turf, outside, also.
On 24 August 2018, I treated two of the mealworm jobs at night. The numbers of larvae were much reduced, but the number of adults had increased significantly.
Daytime wide-area spray applications do not appear to be useful, as there appears to be little effect, on the larvae.
Baiting with Niban also did not seem to have appreciable impact on their numbers, either.
Nighttime wide-area spray applications do reduce numbers. But even then, the results are not as good as I’d have expected. In the tanbark areas, there were still plenty of mealworms, and there were still mealworms crawling around in areas that I’d night-sprayed, just two nights earlier (and had also been day-sprayed).
28 August 2018. In following up on some of the spray applications against the Eurasian mealworms, it is becoming clear that these insects have a resistance to pyrethroid insecticides. We have treated one location five times, with rates varying from 1-3 quarts per 100 gallons of Bifenthrin, and have used Tempo as well, with both daytime and nighttime applications, and the results are not impressive. The applications have greatly reduced the numbers, but it is clear that the insects have resistance. They must be under pesticide pressures in their native areas. This pyrethroid resistance was a surprise to me.
Lori Dunlap recorded these videos showing large numbers of Eurasian mealworms near her home. 29 and 30 August 2018, Sonora area. We see the larvae far from the house, near the house, taking refuge in joints in the concrete, in the garage, in the house, and in the tanbark.
And thanks to Warren Steiner… he had a better name for the video.
Lori Dunlap brought in samples of pupae, and possibly eggs, of the Eurasian mealworm. Here are images of the pupae. Specimens collected 17 August 2018, Sonora area.
One of the pupae managed to make it to adult. Images 15-17, below.
In our first call about Eurasian mealworms, in 2015, the customer said these insects were falling from the ceiling. That was unusual for mealworms, and then, before we knew what species they were, and more about their biology (which is still not properly known), we assumed they had originated in the attic, breeding in a food source there. We could find no such source, and now know that these mealworms readily climb.
In this video, at 6:57, we document the Eurasian mealworms climbing fence posts. And here we provide some video showing how they have no problem climbing rocks.
It is clear now that the attic invasion calls (we have had more, since) are the result of the Eurasian mealworms climbing walls, all the way up into attics, and then down into the living areas of homes. This is indeed an unusual mealworm.
We tested, earlier, two insect baits, Maxforce Quantum Ant Bait, and Maxforce Complete Granular Insect Bait to see if the Eurasian mealworms would eat them. See the food preference videos located here. The mealworms showed no interest in Quantum Ant Bait, but readily accepted the Maxforce Complete Granular Insect Bait.
We wanted to test more granular insect baits, and contacted John Woodward, of Geotech Supply, in Sacramento, who graciously sent us samples of two more baits, Advance 375A Granular Ant Bait, and Advion Insect Granules. In addition, we had Niban Granular Bait in stock, and I took all three baits to the Springfield Road jobsite for testing, on 13 August 2018, at night.
As a control, we used rolled oats, a food we had previously found the Eurasian mealworms readily accepted. We set up six side-by-side choice tests, with the three baits and rolled oats, and videoed the responses over about an hour.
Overall, it seemed that the Eurasian mealworms accepted Advance 375 best, followed closely by Niban, with Advion the least popular bait. We’d previously shown that Maxforce Compete was well accepted.
We could state something like this: (Maxforce Complete=Advance 375=Niban) > Advion. That is, it appears any of the first three would give good results, and then, if needed, one of the other baits could be used later, if needed.
These tests were only to examine how well the baits were accepted by the Eurasian mealworms, not the overall degree of control. Hopefully, we will run those tests soon.
Thank you to Dr. Doug and Sheri Fleming for allowing us to run these tests at their home, and to John Woodward of Geotech Supply for the donation of the insect baits.
We received an email about the presence of hundreds of maggot-like insects in a garage, in the Springfield Road area (near Columbia), 2 August 2018. It appears there had been a migration the night before, from outside, and that there were many hundreds of larvae inside the garage. Service tech Jason Price responded, and brought back samples. They were tenebrionid larvae, often called mealworms, and are the immature stage of darkling ground beetles.
I returned with Jason, to examine the situation myself. This is the residence of Dr. Doug and Sheri Fleming. The exterior was very well maintained. A field, out beyond the driveway, was closely mowed, bone-dry, and did not appear to present much of an environment for them. The ornamentals along the driveway consisted of small olive trees and rosemary. A cardboard mulch was used extensively, under the bark. I found a couple of dead, adult tenebrionids in that area, matching what we’d seen a few years before, in Calaveras County. It appears that the beetles and larvae were feeding and breeding in this strip along the driveway, maybe under the cardboard.
It was, indeed, the same species that had an outbreak in Calaveras County in August 2015. This was the first we’d seen of this odd-ball mealworm invasion in Tuolumne County. Mealworms, as a pest, is not something we experience.
I sent the photos to Dr. Rolf L. Aalbu, of the California Academy of Sciences, a top expert on the tenebrionids of California, (he co-authored the paper), who identified the beetle as Opatroides punctulatus, a relatively new invasive pest. Dr. Aalbu was also a co-author of the 2009 paper first describing this species in California.
That paper gave the discovery and first identification of Opatroides punctulatus in North America, from specimens collected on December 16, 2007, in Sacramento. The area of discovery was near the Sacramento deep water channel, and it is believed that the beetle was introduced to North America, in Sacramento, by way of cargo ships.
In 2008, further search showed that the beetle was present in four counties. This inspired the researchers to re-examine their collections, in which they discovered a specimen collected near the same area, in 2003.
The beetle is common in Europe, Russia, and the general Middle East region.
They report “In California, it is found under stones, leaf litter, scraps of wood, paper and fabrics on sandy clay soil in open disturbed sites.”
I soon was in communication with Dr. Warren E. Steiner, of the Smithsonian Institution, another co-author of the ‘discovery’ paper. Dr. Steiner provided a more recent, 2015, paper, “New Records of Three Non-Native Darkling Beetles (Coleoptera:Tenebrionidae) Established in California and Nevada, USA” coauthored with Dr. Jil Swearingen.
This paper reviewed the California counties in which Opatroides punctulatus had been recorded, and neither Tuolumne or Calaveras were listed. In this paper, they reported that this beetle was now common in Reno. From the paper: “All Nevada specimens were found under rocks and leaf litter in urban roadside areas and often in curb garden plantings.”
This is an important section, cut and pasted, from Steiner & Swearingen paper: “The agricultural pest status of O. punctulatus was reviewed (Aalbu et al. 2009) with mention of its potential as a turf pest. The beetle could also become a household nuisance pest in North America. A fully winged species was observed in Israel to enter a dwelling “attracted by lights” Kaufmann 1969) and soon after was found feeding on various stored foods. Kaufmann (1969) found O. punctulatus to be omnivorous and “preferred meat to all other food”, including both raw and cooked meat of several kinds; on a diet of cereal alone, development of larvae to adults was proven doubtful, but those feeding on meat grew faster, larger, and with more vigor. Our observation of the cluster of beetles under a dead vole suggests that, while moisture may be the initial attractant, carrion may serve as food for the breeding of O. punctulatus in the field, given suitable soil conditions and other ecological factors. ”
On December 26, 2007, photos of this beetle were uploaded to BugGuide.net for ID. The ID was made by Dr. Kojun Kanda, another of the authors of the ‘discovery paper’. The specimens came from Cool, in El Dorado County. So the beetles had spread out quickly from Sacramento.
We have established now that the beetle can be a household nuisance pest, given the number of cases we have seen in both counties.
At the Fleming’s home, Sheri tells us that the larvae are attracted to light. She reports: “Last night we kept the lights off, but I walked the driveway with a flashlight after 9 pm and discovered they are migrating from the entire length of the driveway on both sides and coming up from the cardboard/mulch. They are active at night – but Doug went out pre-dawn and there was no activity. Incidentally, it is a very long driveway. So the migrating population is in the many thousands. She also said: “They migrate to cracks and under objects.” The best guess is that the larvae are searching for a better place to pupate.
For thoroughness, here is the Conclusion from the 2009 paper, Opatroides punctulatus Brulle´ now established in California by Rolf L. Aalbu, Kojun Kanda, and Warren E. Steiner.
“Opatroides punctulatus will likely become a common insect of lawns and turf in residential areas of central California and its spread to other regions should be monitored. Agricultural pest status may also need study; members of the related genera Ulus and Blapstinus have been known to damage seedlings (see papers discussed by Steiner 2003) in the southwestern states. In a translation from Russian, Medvedev (1968) lists O. punctulatus among ‘‘pests of consequence’’ and uses the common name, ‘‘cotton beetle’’ and adds that ‘‘In Transcaucasia and Soviet Central Asia the adult beetles and larvae damage melons, pumpkins, cotton, tobacco, cereals, vine, young seedlings. In Tadjikistan, it is found in granaries and barns.’’ In addition, Opatroides punctulatus was listed as a pest of cereals, cotton, grapes, melons, mulberry trees, pumpkins, soybeans and tobacco in the countries of Cyprus, India, Libya, Turkey and Russia (‘‘USSR’’) by Allsopp (1980) and a ‘‘dominant potential pest’’ of cotton in Russia (Sugonyaev 1994). The true pest status of Opatroides and necessity of taking control measures should be carefully evaluated. Like most tenebrionid beetles or false wireworms, Opatroides larvae are general feeders which may gnaw and feed on subsurface roots and seedlings. Economic damage may result only if these larvae become very abundant.”
The Eurasian Mealworm
Being that there is no common name for Opatroides punctulatus, and it is becoming a widespread pest species, we need a name. The Eurasian mealworm tells us it is an introduced pest, and what nearly everyone will notice first are the larvae, which look like mealworms. So we have it: the Eurasian mealworm.
There is a new pest in both Calaveras and Tuolumne Counties. They are presenting issues as a nuisance pest, often in large numbers, invading homes and garages, as they also did in Mountain Ranch and Valley Springs. This beetle is the second new invasive pest we have seen this year, 2018. We previously reported on the snail-case bagworm.
The research papers are added at the bottom of this post.
Below are videos showing:
1. how many were under a sofa being stored inside the garage. I want to make it clear that the beetle larvae were under almost everything in the garage.
2. Next is a compilation of night videos, taken 5 August 2018, at the Fleming residence, and then in other areas of Springfield Estates. We see in the night video, that both adults and several sizes of larvae, are out foraging. Along the driveway area, the density is high, but I found adult and larvae in an adjacent open field, 100+ feet from the driveway area. I also found adults and larvae, in lower density, along Bennett Drive as well, far from any house. We have video here that shows the larvae climbing up wooden fence posts, providing further evidence of their climbing ability. This leads me to think that Opatroides punctulatus is a nocturnal surface forager.
3. Feeding experiments. These show that Opatroides punctulatus is a nocturnal, general scavenger that prefers protein and fat, either as animal or plant. In this video, we also tested two insect baits: Maxforce Quantum ant bait, which was ignored totally, and Maxforce Complete Granular insect bait, which was readily accepted.
Thanks to Dr. Rolf Aalbu, Dr. Warren Steiner, and Dr. Lynn Kimsey for providing these research papers.
Life history of Opatroides punctulatus
(This is the page we uploaded in August 2015, before we had positive identification of the Eurasian mealworms.)
These are specimens of a type of tenebrionid larvae (mealworm-like larvae, that turn into darkling beetles) found within homes.
The first set is from Mountain Ranch, CA. 25 August 2015. Specimens collected by Trevor Cuthill. Specimens were in various locations throughout the house, but most prevalent along the baseboard of the exterior wall in the living room.
Second set is from a home in Valley Springs, in a shop area. Specimens collected by Ryder Richards, 20 July 2016. Ryder reports the room had lots of sawdust.
Third set are photos of the adult beetles, collected by Ryder Richards from a Valley Springs job site.
Thanks to Dr. Lynn Kimsey for confirmation of the ID.
In our cases, within these homes, we have not found what these larvae are eating. Our best guess is that these are lesser mealworms. We are still looking to find the food source for them.
Click on an image to enlarge it.
Mealworm larvae from within a house
Second set. Valley Springs, July 2016.