- Author: Thomas J Getts
I have gotten quite a few calls about blister beetles this year. There was a newspaper article up in Modoc that caused some stir, and was picked up by a lot of social media pages. So, what are blister beetles and why do we care?
Blister beetles get their name for a reason. They contain the toxin cantharidin, which can be excreted when they are threatened, or crushed which causes bad blisters on the skin. While this is problematic they typically are not drawn to humans, and blisters can be avoided by not handling them. Where they pose a larger problem is as a contaminant of hay, where they can be crushed/killed and incorporated into a bale posing as a potential toxin to be consumed by livestock.
Photo One: Blister Beetle on Musk Thistle next to a Roadway
Let's take a step back. What are blister beetles and why are they a subject of conversation now? There are numerous native blister beetles in California. Some are striped, some are brightly colored, but most of the ones I have been seeing are black or grey. The immature larvae of blister beetles feed on the eggs of grasshoppers or ground dwelling bees. I don't have to tell anyone in the Intermountain region, we have had quite a few bad grasshopper years which has led to an increase in blister beetle populations. Typically, the adults lay eggs right on top of the egg beds of grasshoppers. I'd be on the lookout for blister beetles the rest of this year, and definitely next year as they feast on the eggs underground. (So, they are not all bad as they kill some hoppers!).
Photo Two: Grasshoppers flying away from an ATV in a pasture up in Modoc County
As adults, they can consume forage, but typically they are drawn to flowers and consume pollen. (Different species have different preferences.) I have mainly seen them on roadsides, trail sides, and rangelands where there are flowering plants. In hay fields I have only seen them in “native hay pastures” that have wildflowers. However I have gotten reports of them being on the edges of some alfalfa fields that have started to go to bloom.
For livestock generally they are only problematic when they get caught up in a bale. How many is too many? This is a good question. Numerous extension publications cite research done back in the 80's looking at how many blister beetles it would take to kill a horse (horses are more susceptible to the toxin than cattle of sheep). As with all toxin's it often depends on numerous factors, and there is not a single number of beetles that will kill a horse every time. The amount of toxin per beetle can vary by species of beetle as well as within species of beetle. From the research done in the 80's the cantharidin content per beetle ranges from 0.5mg to 5mg, and is toxic to horses at the tune of 1mg/kg. This means that there can be a huge range of how many beetles it will take to kill a horse (see table one). With that being said while it may take a significant number of beetles to kill a horse, as few as five beetles can start to cause colic.
Table one: Adapted from Capinera et al. 1985. J. Econ. Entomol. 78:1052-55.
So, what do you do about the beetles? One of the best things to do is scout fields before they are cut to make sure you do not have them in the field. While it might be counter your management objectives to maximize yield during the mid-season cuttings, cutting alfalfa or clover before bloom can reduce the incentive of beetles to move into hay fields. It is also important the keep a clean hay field, and reduce the number of weeds that may flower in the field drawing the beetles in. There are insecticides like (Sevin- carbaryl, or Warrior- lambda-cyhalothrin) which are effective at killing blister beetles in forages, but may pose their own drawbacks. While most of the beetles should die and fall down to the ground after an insecticide application, there is still some potential for them to be incorporated into the hay during the cutting and raking process. Likewise, the pre harvest intervals for these materials can delay cutting and could require driving over a lot of hay, if an aerial applicator is not available. Cutting around infested patches or isolating/discarding hay that may be contaminated, could be a prudent strategy. Likewise waiting until the beetles move out of the field could be an option.
Photo Three: Blister beetles on clover in a "native" hay meadow in the Intermountian region
There are over 300 species of blister beetles in North America, and not all have been tested for their Cantharidin content. When haying especially using modern equipment with conditioners, I urge you to be cautious, and take time to scout fields before cutting, especially if that hay is going to the horse market.
For more information there are some excellent extension publications online from UCIPM, Colorado State University and North Dakota State.
Photo Five: Blister Beetle on Feral Rye next to the Susan River in Lassen County
- Author: Kathy Keatley Garvey
Blister beetles (family Meloidae) are so named because they emit a poisonous chemical, cantharidin, that can blister your skin. Don't even think about touching them!
Blister beetles can infest alfalfa hay, and are toxic--even deadly--to livestock. See "Blister Beetles" published by the Montana Agricultural Experiment Station.
But did you know that...
Blister beetles are pollinators!
We recently saw a blister beetle eating pollen on a Mexican sunflower, Tithonia rotundifola. We've also seen this insect transferring pollen.
But we have yet to hear someone shout out "blister beetle" when a speaker asks the audience for a list of pollinators.
But they are pollinators...Just think of all the alliteration...bees, butterflies, beetles, birds and bats...and the double alliteration, "blister beetles."
![A blister beetle (family Meloidae) eating pollen from the Mexican sunflower, Tithonia rotundifola. (Photo by Kathy Keatley Garvey) A blister beetle (family Meloidae) eating pollen from the Mexican sunflower, Tithonia rotundifola. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/107760.jpg)
- Author: Kathy Keatley Garvey
If you're feeling overwhelmed during the holiday season and just can't seem to concentrate, check out the focus and intensity of this male territorial bee, a Melissodes agilis.
It was back in July of 2015 when I spotted a meloid beetle on a Mexican sunflower, Tithonia rotundifola, in a Vacaville pollinator garden.
The Melissodes did, too.
Now the meloid beetle is a blister beetle (family Meloidae). Don't touch these beetles because they emit a poisonous chemical, cantharidin, that can blister your skin. It makes for great defense. Touch me, and I'll blister your skin. No wonder the chemical is used to remove warts.
Blister beetles are also known to infest alfalfa hay, and are toxic--even deadly--to livestock. See "Blister Beetles" published by the Montana Agricultural Experiment Station.
"Cantharidin, a vesicant produced by beetles in the order Coleoptera, has a long history in both folk and traditional medicine...Historically, cantharidin has been used as an aphrodisiac, an abortifacient, and a veterinary medicine diuretic." --Cantharidin Revisited, JAMA Dermatology.
So here's this bee targeting the beetle. Oh, the intensity of those eyes...much like a last-minute shopper eyeing a 50 percent-off gift, the last in stock, and ignoring the attempts of last-minute shoppers to grab it.
Did the beetle move?
Not a bit. It rose and ate some of the pollen that the bee was trying to save for its own species.
![A male Melissodes agilis targeting a meloid beetle on a Tithonia in a Vacaville garden. (Photo by Kathy Keatley Garvey) A male Melissodes agilis targeting a meloid beetle on a Tithonia in a Vacaville garden. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/103902.jpg)
![The blister beetle eating pollen. (Photo by Kathy Keatley Garvey) The blister beetle eating pollen. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/103903.jpg)
- Author: Kathy Keatley Garvey
However, there may be sad ending...more about that later.
Members and their guests will gather Nov. 7 at 9:15 a.m. at their meeting site, the Contra Costa Mosquito and Vector Control District conference room, 155 Mason Circle, Concord. for coffee and registration.
Then, at 9:30 a.m., Saul-Gershenz will discuss “Meloid Parasites of Solitary Bees." A graduate student in the Neal Williams lab, UC Davis Department of Entomology and Nematology, and a co-founder of SaveNature.Org, Saul-Gershenz researches a solitary ground-nesting bee, Habropoda pallida and its nest parasite, a blister beetle, Meloe franciscanus, found in the Mojave National Preserve.
She is the lead author of “Blister Beetle Nest Parasites Cooperate to Mimic the Sex Pheromone of the Solitary Bee Habropoda pallida (Hymenoptera: Apidae)," co-authored by professor Jocelyn G. Millar and staff research associate J. Steven McElfresh, both of UC Riverside. The Mojave National Preserve Science News published the peer-reviewed research in its April 2012 edition.
"The solitary bee is the first native bee to emerge in the spring on the Kelso Dunes in the Mojave National Preserve," said Saul-Gershenz. “The adult beetles emerge on the dunes in the winter months at Kelso Dunes and feed exclusively on the leaves of Astragalus lentiginosus, which leafs out in January."
The bee's emergence is generally synchronized with the onset of blooms of the Borrego milkvetch, which is the sole host plant of adults of the blister beetle at Kelso Dunes.
The UC Davis ecologist said the larvae of the parasitic blister beetle produce a chemical cue or a pheromone similar to that of a female solitary bee to lure males to the larval aggregation. The larvae attach to the male bee and then transfer to the female during mating. The end result: the larvae wind up in the nest of a female bee, where they eat the nest provisions and likely the host egg.
The work of Saul-Gershenz, Millar and McElfresh appears in a newly published academic book, Sensory Ecology, Behaviour, and Evolution (Oxford University Press) by Martin Stevens. Another book, pending publication in December, also will contain their work: the second edition of Pheromones and Animal Behaviour (Cambridge University) by Tristram Wyatt.
Previously, three other books summarized their research:
Keeping the Bees: Why All Bees Are at Risk and What We Can Do to Save Them by Laurence Packer and published in 2011 by HarperCollins Publishers, Ltd.
Cuticular Hydrocarbons: Biology, Biochemistry and Chemical Ecology by editors A. Bagnères-Urbany and G. Bloomquist and published in 2010 by Cambridge University Press.
The Other Insect Societies by James T. Costa, and published in 2006 by the Belknap Press of Harvard University Press.
Now, back to what may be a sad ending.
Following Saul-Gershenz' one-hour talk, the Nor Cal Entomology Society members will discuss the future of the organization, founded in 1930. Then it was known as the Northern California Entomology Club. Membership continues to be open to all interested persons, with dues at $10 a year. Currently the society meets three times a year: in Sacramento, at UC Davis, and in Concord.
Nor Cal Entomology president Robert Dowell of the California Department of Food and Agriculture will moderate the disussion.
“We have reached a critical juncture in the existence of the organization,” secretary-treasurer Eric Mussen, Extension apiculturist with the UC Davis Department of Entomology and Nematology, wrote to the members in an email. “At its beginning, the society served as the meeting place for entomologists mostly from UC Berkeley and UC Davis, as well as other members who appreciated their lively discussions of research and pest control. Representatives from industry and regulatory establishments also participated. A revolving system of society chairs was instituted and membership was good.”
“Over time, the climate has changed. UC Berkeley no longer has an entomology department or hardly any entomologists anymore,” said Mussen, who will retire from UC Davis in June 2014.
Those planning to attend to hear the talk and discuss the future of the organization should contact Mussen at ecmussen@ucdavis.edu or telephone him at (530) 753-0472 by Nov. 1. And oh, yes, there's a luncheon to be served by Kinder's Meats. Mussen is taking reservations (and payment) for that, too.
![A digger bee, Habropoda pallida, with blister beetle larvae. (Photo by Leslie Saul-Gershenz) A digger bee, Habropoda pallida, with blister beetle larvae. (Photo by Leslie Saul-Gershenz)](/blogs/blogcore/blogfiles/19091.jpg)
- Author: Kathy Keatley Garvey
Her one-hour talk, “Meloid Parasites of Solitary Bees,” begins at 9:30 a.m. The Nor Cal Entomology Society meets three times a year: Sacramento, Davis and Concord.
Saul-Gershenz, a graduate student in the Neal Williams lab, UC Davis Department of Entomology and Nematology, and a co-founder of SaveNature.Org, researches a solitary ground-nesting bee, Habropoda pallida and its nest parasite, a blister beetle, Meloe franciscanus, found in the Mojave National Preserve.
The meeting begins at 9:15 a.m. with coffee and registration for club members and their guests. The remainder of the meeting will be devoted to the future of the society, with president Bob Dowell of the California Department of Food and Agriculture moderating the discussion.
Saul-Gershenz is the lead author of “Blister Beetle Nest Parasites Cooperate to Mimic the Sex Pheromone of the Solitary Bee Habropoda pallida (Hymenoptera: Apidae)," co-authored by professor Jocelyn G. Millar and staff research associate J. Steven McElfresh, both of UC Riverside. The peer-reviewed research was published in the April 2012 edition of the Mojave National Preserve Science News.
The bee's emergence is generally synchronized with the onset of blooms of the Borrego milkvetch, which is the sole host plant of adults of the blister beetle at Kelso Dunes.
The UC Davis ecologist said the larvae of the parasitic blister beetle produce a chemical cue or a pheromone similar to that of a female solitary bee to lure males to the larval aggregation. The larvae attach to the male bee and then transfer to the female during mating. The end result: the larvae wind up in the nest of a female bee, where they eat the nest provisions and likely the host egg.
The work of Saul-Gershenz, Millar and McElfresh appears in a newly published academic book, Sensory Ecology, Behaviour, and Evolution (Oxford University Press) by Martin Stevens. Another book, pending publication in December, also will contain their work: the second edition of Pheromones and Animal Behaviour (Cambridge University) by Tristram Wyatt.
Previously, three other books summarized their research:
- Keeping the Bees: Why All Bees Are at Risk and What We Can Do to Save Them by Laurence Packer and published in 2011 by HarperCollins Publishers, Ltd.
- Cuticular Hydrocarbons: Biology, Biochemistry and Chemical Ecology by editors A. Bagnères-Urbany and G. Bloomquist and published in 2010 by Cambridge University Press.
- The Other Insect Societies by James T. Costa, and published in 2006 by the Belknap Press of Harvard University Press.
Following her talk, beginning at 10:45 a.m., the Nor Cal Entomology Society members will discuss the future of the organization.
“We have reached a critical juncture in the existence of the organization,” secretary-treasurer Eric Mussen, Extension apiculturist with the UC Davis Department of Entomology and Nematology and a co-founder of the society, wrote to the members in an email. “At its beginning, the society served as the meeting place for entomologists mostly from UC Berkeley and UC Davis, as well as other members who appreciated their lively discussions of research and pest control. Representatives from industry and regulatory establishments also participated. A revolving system of society chairs was instituted and membership was good.”
“Over time, the climate has changed. UC Berkeley no longer has an entomology department or hardly any entomologists anymore.”
Mussen, one of the most active members of the group, will be retiring from the university in June 2014.
Those planning to attend should contact Mussen at ecmussen@ucdavis.edu or telephone him at (530) 753-0472 by Nov. 1. The lunch will be catered by Kinder’s Meats.
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