Life cycle, damage, and treatment of blister beetles, including ramifications for horses and damage prevention

Campbell, John B.

Ensley, Steve

English

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 2002 Management of Blister Beetles in Alfalfa John B. Campbell University of Nebraska - Lincoln, jcampbell1@unl.edu Steve Ensley Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Campbell, John B. and Ensley, Steve, "Management of Blister Beetles in Alfalfa" (2002). Historical Materials from University of Nebraska-Lincoln Extension. 92. https://digitalcommons.unl.edu/extensionhist/92 This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. C-13NF551Management of Blister Beetles in AlfalfaBy John B. Campbell, Extension EntomologistSteve Ensley, Extension Veterinarian and ToxicologistAdult blister beetles (Epicauta spp.) tend to be gregari-ous, and several may be observed feeding on the sameflowering plant such as alfalfa or sometimes soybeans, gold-enrod or occasionally musk thistle. They feed primarily onleaves and flowers but do little damage to crops.Adult blister beetles vary in size and color but can berecognized by elongated, narrow, cylindrical and soft bodies.When viewed from above, they have a constriction behind thehead where it attaches to the narrowed anterior end of thethorax. In Nebraska, the three-striped, gray and black blisterbeetles are the most common species. The three-striped islong, slender, brown and yellowish-gray with yellowish stripes.The gray is a larger beetle that is 9/16 inch to 11/16 inch long.The gray coloring is due to a thick covering of hair. The blackblister beetle is the largest of the three species. It is morerobust and is 5/8 inch to 7/8 inch long.Life CycleMost blister beetle larvae feedon grasshopper eggs, so often theirnumbers may be higher where thereare high numbers of grasshoppers.Consequently, there probably willbe more blister beetles in the yearfollowing large grasshopper num-bers. The life cycle of the blisterbeetle is complex and includes sev-eral immature forms. Females depositclusters of eggs in depressions in theground. Newly hatched larvae movethrough the soil, feeding on grass-hopper egg pods. This larval stage istermed “triungulin”. Within a month,the larvae pass through three moregrowth stages with each becomingmore sedentary. Finally, they changeto a pseudopupae, which is the over-wintering stage. As temperature andmoisture increase in the spring, they enter the final immaturepupal stage from which adults emerge. There is one generationper year. Adult blister beetles can generally be found in alfalfathrough the second and third cuttings and some years into thefourth cutting. Some species are also predaceous in the larvalcells of ground-dwelling bees.DamageThe interest in blister beetles is not due to potential plantdamage, but rather the potential injury to horses or lesscommonly to cattle and sheep if they ingest blister beetles withharvested forage (Ray et al. 1989), (Gayle et al. 1981). Thebodies of blister beetles contain a lipid soluble blistering agentcalled cantharidin. Cantharidin causes blisters on skin tissueupon contact.Horses are particularly susceptible to blister beetle poi-soning. Part or all of a horse’s digestive tract can be severelyirritated, leading to secondary infections and bleeding(Bauernfeind and Breeden 1984). Cantharidin is absorbed andBlack Blister Beetle Three-striped Blister Beetle Gray Blister BeetleFile under: INSECTS & PESTSC-13, Field CropsIssued August, 2002Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Countiesand the United States Department of Agriculture.University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–Lincolnand the United States Department of Agriculture.© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.excreted through the kidneys, thus irritation of the kidneys,ureter, urinary bladder and urethra could be followed bysecondary infections and bleeding. The substance also low-ers serum calcium levels and causes damage to heart muscletissue.Capinera et al. (1985) conducted a cantharidin analysis onseveral species of blister beetles commonly found in Colo-rado. They found differences in amounts found among spe-cies and sexes. Males produce cantharidin and pass it tofemales at mating. The minimum lethal dose of cantharidin isabout 1 mg/Kg body weight of a horse. The lethal dose forcattle may be as low as 0.5 mg/Kg body weight (Gayle, 1981).Consequently, a few beetles with a high cantharidin levelwould kill a small horse, but quite a few with a low level wouldbe required to kill a larger horse. These researchers estimatethat it would require 1700 black blister beetles to kill an 825-pound horse, but only 120 three-striped blister beetles. How-ever, only 40 three-striped blister beetles would kill a 275-poundcolt. As little as 4-6 grams of dried beetles can be fatal to ahorse.Signs and symptoms of cantharidin poisoning in a horsemay include blisters and ulcers in the mouth, gastritis, esoph-agitis, edema of the submucosa of the intestine, colic, diarrheaand blood and mucous in the stool. Other signs includefrequent attempts to urinate but voiding of little urine andblood in the urine. The lowered blood serum calcium levelsmay cause body tremors and a breathing pattern characterizedby a periodic jerking contraction of the diaphragm (synchro-nous diaphragmatic flutter) associated with the heartbeat.Poisoned horses may place the muzzle in water without drink-ing, have an increased temperature, increased pulse andbreathing rate, be dehydrated, depressed and in shock. Oraland gastrointestinal ulcerations may be observed in cattle andsheep. If cantharidin poisoning is suspected, consult a veteri-narian.To diagnose blister beetle toxicosis, there need to beappropriate clinical signs and presence of the beetle. Someveterinary diagnostic laboratories can analyze hay, urine,serum or gastric content for cantharidin concentration.TreatmentThere is no specific antidote for cantharidin. Treatment isdirected toward supportive care. The gastrointestinal tractneeds to be decontaminated by activated charcoal and mineraloil. Fluid therapy and bicarbonate need to be used to alleviateshock and acidosis. Calcium also may be needed.Prevention or AvoidanceToxicosis by blister beetles is related to simultaneouscutting and crimping of hay when beetles are present. If hayis cut with a sickle bar or rotary mower and not crimped, thebeetle can leave the hay after it is cut. If the beetles are notallowed to escape, the trapped beetles die and are incorpo-rated into the hay. In Nebraska, first cutting of alfalfa usuallyoccurs before blister beetle adults are present so horse ownerscould be fairly safe in buying first cutting alfalfa. Use hayharvested before mid-May or after early September whenblister beetles are less apt to be present. Scout fields, par-ticularly in border areas for the presence of blister beetlesand if found, treat with a short residual insecticide beforecutting. Insecticides approved for use on alfalfa can befound on the UNL Department of Entomology web site athttp://entomology.unl.edu. When selecting a pesticide, readthe label to determine harvest restriction intervals. KansasState University doesn’t recommend blister beetle treatmentbecause the dead beetles, which are still toxic, remain in thefield. Other recommendations include not using crimpers onhay intended for horses and cutting alfalfa in the bud stagebecause blooms attract blister beetles.It is difficult to eliminate the possibility of blister beetlesin alfalfa. Examining hay bales prior to purchase is difficultbecause the beetles tend to congregate, so most bales may befree of beetles, but a few may contain enough beetles to causetoxicity in horses. Careful examination when feeding alfalfamay allow detection of beetles if present.ResourcesBauernfeind, R.J. and L.D. Breeden. 1984. Blister beetles.Kansas State University Extension Service AgFacts En-tomology. 111. 4 pp.Capinera, J.L., D.R. Gardner and F.R. Stermitz. 1985. Canthari-din levels in blister beetles (Coleoptera: Meloidae) asso-ciated with alfalfa in Colorado. Journal of EconomicEntomology. 78: 1052-55.Gayle, L.G., J.C. Reagor, A. Ray and E.M. Bailey. 1981. Canthari-din poisoning in cattle. American Veterinary MedicalAssociation 118th Annual Meeting. 1997.Ray, A.C., A.L. Kyle, M.J. Murphy and J.C. Reagor. 1989.Etiologic agents, incidence and improved diagnosticmethods of cantharidin toxicosis in horses. AmericanJournal of Veterinary Research 50, 187-191.

Management of Blister Beetles in Alfalfa

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Historical Materials from University of 
Nebraska-Lincoln Extension Extension 
2002 
Management of Blister Beetles in Alfalfa 
John B. Campbell 
University of Nebraska - Lincoln, jcampbell1@unl.edu 
Steve Ensley 
Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist 
 Part of the Agriculture Commons, and the Curriculum and Instruction Commons 
Campbell, John B. and Ensley, Steve, "Management of Blister Beetles in Alfalfa" (2002). Historical 
Materials from University of Nebraska-Lincoln Extension. 92. 
https://digitalcommons.unl.edu/extensionhist/92 
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - 
Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an 
authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
C-13
NF551
Management of Blister Beetles in Alfalfa
By John B. Campbell, Extension Entomologist
Steve Ensley, Extension Veterinarian and Toxicologist
Adult blister beetles (Epicauta spp.) tend to be gregari-
ous, and several may be observed feeding on the same
flowering plant such as alfalfa or sometimes soybeans, gold-
enrod or occasionally musk thistle. They feed primarily on
leaves and flowers but do little damage to crops.
Adult blister beetles vary in size and color but can be
recognized by elongated, narrow, cylindrical and soft bodies.
When viewed from above, they have a constriction behind the
head where it attaches to the narrowed anterior end of the
thorax. In Nebraska, the three-striped, gray and black blister
beetles are the most common species. The three-striped is
long, slender, brown and yellowish-gray with yellowish stripes.
The gray is a larger beetle that is 9/16 inch to 11/16 inch long.
The gray coloring is due to a thick covering of hair. The black
blister beetle is the largest of the three species. It is more
robust and is 5/8 inch to 7/8 inch long.
Life Cycle
Most blister beetle larvae feed
on grasshopper eggs, so often their
numbers may be higher where there
are high numbers of grasshoppers.
Consequently, there probably will
be more blister beetles in the year
following large grasshopper num-
bers. The life cycle of the blister
beetle is complex and includes sev-
eral immature forms. Females deposit
clusters of eggs in depressions in the
ground. Newly hatched larvae move
through the soil, feeding on grass-
hopper egg pods. This larval stage is
termed “triungulin”. Within a month,
the larvae pass through three more
growth stages with each becoming
more sedentary. Finally, they change
to a pseudopupae, which is the over-
wintering stage. As temperature and
moisture increase in the spring, they enter the final immature
pupal stage from which adults emerge. There is one generation
per year. Adult blister beetles can generally be found in alfalfa
through the second and third cuttings and some years into the
fourth cutting. Some species are also predaceous in the larval
cells of ground-dwelling bees.
Damage
The interest in blister beetles is not due to potential plant
damage, but rather the potential injury to horses or less
commonly to cattle and sheep if they ingest blister beetles with
harvested forage (Ray et al. 1989), (Gayle et al. 1981). The
bodies of blister beetles contain a lipid soluble blistering agent
called cantharidin. Cantharidin causes blisters on skin tissue
upon contact.
Horses are particularly susceptible to blister beetle poi-
soning. Part or all of a horse’s digestive tract can be severely
irritated, leading to secondary infections and bleeding
(Bauernfeind and Breeden 1984). Cantharidin is absorbed and
Black Blister Beetle Three-striped Blister Beetle Gray Blister Beetle
File under: INSECTS & PESTS
C-13, Field Crops
Issued August, 2002
Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Counties
and the United States Department of Agriculture.
University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–Lincoln
and the United States Department of Agriculture.
© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.
excreted through the kidneys, thus irritation of the kidneys,
ureter, urinary bladder and urethra could be followed by
secondary infections and bleeding. The substance also low-
ers serum calcium levels and causes damage to heart muscle
tissue.
Capinera et al. (1985) conducted a cantharidin analysis on
several species of blister beetles commonly found in Colo-
rado. They found differences in amounts found among spe-
cies and sexes. Males produce cantharidin and pass it to
females at mating. The minimum lethal dose of cantharidin is
about 1 mg/Kg body weight of a horse. The lethal dose for
cattle may be as low as 0.5 mg/Kg body weight (Gayle, 1981).
Consequently, a few beetles with a high cantharidin level
would kill a small horse, but quite a few with a low level would
be required to kill a larger horse. These researchers estimate
that it would require 1700 black blister beetles to kill an 825-
pound horse, but only 120 three-striped blister beetles. How-
ever, only 40 three-striped blister beetles would kill a 275-pound
colt. As little as 4-6 grams of dried beetles can be fatal to a
horse.
Signs and symptoms of cantharidin poisoning in a horse
may include blisters and ulcers in the mouth, gastritis, esoph-
agitis, edema of the submucosa of the intestine, colic, diarrhea
and blood and mucous in the stool. Other signs include
frequent attempts to urinate but voiding of little urine and
blood in the urine. The lowered blood serum calcium levels
may cause body tremors and a breathing pattern characterized
by a periodic jerking contraction of the diaphragm (synchro-
nous diaphragmatic flutter) associated with the heartbeat.
Poisoned horses may place the muzzle in water without drink-
ing, have an increased temperature, increased pulse and
breathing rate, be dehydrated, depressed and in shock. Oral
and gastrointestinal ulcerations may be observed in cattle and
sheep. If cantharidin poisoning is suspected, consult a veteri-
narian.
To diagnose blister beetle toxicosis, there need to be
appropriate clinical signs and presence of the beetle. Some
veterinary diagnostic laboratories can analyze hay, urine,
serum or gastric content for cantharidin concentration.
Treatment
There is no specific antidote for cantharidin. Treatment is
directed toward supportive care. The gastrointestinal tract
needs to be decontaminated by activated charcoal and mineral
oil. Fluid therapy and bicarbonate need to be used to alleviate
shock and acidosis. Calcium also may be needed.
Prevention or Avoidance
Toxicosis by blister beetles is related to simultaneous
cutting and crimping of hay when beetles are present. If hay
is cut with a sickle bar or rotary mower and not crimped, the
beetle can leave the hay after it is cut. If the beetles are not
allowed to escape, the trapped beetles die and are incorpo-
rated into the hay. In Nebraska, first cutting of alfalfa usually
occurs before blister beetle adults are present so horse owners
could be fairly safe in buying first cutting alfalfa. Use hay
harvested before mid-May or after early September when
blister beetles are less apt to be present. Scout fields, par-
ticularly in border areas for the presence of blister beetles
and if found, treat with a short residual insecticide before
cutting. Insecticides approved for use on alfalfa can be
found on the UNL Department of Entomology web site at
http://entomology.unl.edu. When selecting a pesticide, read
the label to determine harvest restriction intervals. Kansas
State University doesn’t recommend blister beetle treatment
because the dead beetles, which are still toxic, remain in the
field. Other recommendations include not using crimpers on
hay intended for horses and cutting alfalfa in the bud stage
because blooms attract blister beetles.
It is difficult to eliminate the possibility of blister beetles
in alfalfa. Examining hay bales prior to purchase is difficult
because the beetles tend to congregate, so most bales may be
free of beetles, but a few may contain enough beetles to cause
toxicity in horses. Careful examination when feeding alfalfa
may allow detection of beetles if present.
Resources
Bauernfeind, R.J. and L.D. Breeden. 1984. Blister beetles.
Kansas State University Extension Service AgFacts En-
tomology. 111. 4 pp.
Capinera, J.L., D.R. Gardner and F.R. Stermitz. 1985. Canthari-
din levels in blister beetles (Coleoptera: Meloidae) asso-
ciated with alfalfa in Colorado. Journal of Economic
Entomology. 78: 1052-55.
Gayle, L.G., J.C. Reagor, A. Ray and E.M. Bailey. 1981. Canthari-
din poisoning in cattle. American Veterinary Medical
Association 118th Annual Meeting. 1997.
Ray, A.C., A.L. Kyle, M.J. Murphy and J.C. Reagor. 1989.
Etiologic agents, incidence and improved diagnostic
methods of cantharidin toxicosis in horses. American
Journal of Veterinary Research 50, 187-191.


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Management of Blister Beetles in Alfalfa

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