Blister of Montana by Sue Blodgett, MSU Extension IPM Specialist; Patricia M. Denke, Research Associate, MSU Dept. of Entomology; and Virginia Knerr, Broadwater County MSU Extension Agent

Blister beetles (meloid beetles) are leaf-feeding that secrete a liquid that can cause blisters, and can be toxic when accidentally fed to livestock in forage. Of nine species observed in Montana, only one has been reported to have damaged crops. This fact sheet describes the species found in MT200209 AG Issued 12/2002 Montana and discusses the risks of crop damage and livestock poisoning.

LISTER BEETLES, also called meloid beetles, get their name from a toxin called cantharidin Bfound in their body fluids. When the adult is disturbed, “blood” containing this toxin is exuded from the leg joints. The fluid can cause blisters when it comes in contact with the skin. Figure 2. Beetles killed during har- Spotted vest operations and incorporated into baled alfalfa can be toxic when feeding on fed to livestock. However, surveys alfalfa flowers (top). Spotted of blister beetles species and sea- blister beetle sonal occurrences conducted over compared to several years in Montana have con- E. oregona cluded that they are of minor con- Figure 1. Typical blister beetle (larger beetle) (right). cern to alfalfa producers or people with distinct narrow neck, long, who feed hay produced in Montana. soft wing covers and tip of abdo- feeding on canola flowers and green men showing. Damage and risk posed by seedpods in Montana but the eco- blister beetles direct pest in alfalfa forage, although nomic impacts are not known. Many species of blister beetles oc- adult feeding may cause localized In contrast to its damage po- cur throughout the United States and defoliation. The primary concern tential, the most well-represented Montana. The species group for each with blister beetles in alfalfa is the blister beetle genus in Montana, region, their seasonal occurrence, potential of contaminating forage Epicauta, can also be considered abundance during the growing season, with the toxin, cantharidin. This hap- beneficial because the immature and the beetleʼs toxicity dictate the pens when beetles are killed during beetles feed on grasshopper eggs. seriousness of this pest. Blister beetles alfalfa harvest and the dried beetles, are documented leaf-feeding pests of which still contain the toxin, are Description potatoes, sugarbeets, and incorporated into baled alfalfa. The blister beetle adult is distin- alfalfa. In Montana, they occur most In other crops such as canola, guished by the long cylindrical soft frequently in alfalfa hay and canola, potatoes or sugarbeets, feeding by body, with the tip of the abdomen but have been reported from potatoes adult blister beetles may cause se- extending beyond the end of the wing and other broadleaf crops. rious defoliation and may damage covers (elytra), chewing mouthparts, Blister beetles can be both direct or destroy flowers or buds, both and a thorax (neck) narrower than and indirect pests depending on of which have impacts on yield both the head and the abdomen (Fig the crop and damage potential. For and quality of the harvested crop. 1). Species range in size from 1/4 example, they are not considered a Blister beetles have been observed inch to almost 1-3/4 inches. Indi- B-20 Meloidae species May June July August September Canola: A large (1 - 1-1/4 inch),

E. fabricii purple and green iridescent beetle ( nuttalli or Nuttallʼs blister L. cyanipennis beetle) can be found in Montana feed- ing on the leaves, stems and flowering E. normalis heads of canola plants. This species E. maculata can be found in dense groups on the

E. sericans edges of canola fields and have been observed moving from windbreaks of E. ferruginea caragana hedges into flowering canola fields. From observations made on E. pensylvanica this species in Canada, they seemed to prefer low- (canola) rather than high- E. murina glucosinolate strains of rapeseed, and E. nuttalli low- rather than high-coumarin strains of sweet clover. This species of blister Occurence from museum beetle stands out because of its large size and metallic coloration. The de- Occurence from field survey foliation damage that they cause does Figure 3. Seasonal distribution of nine blister beetle species in Montana not have significant economic impact data obtained from museum and field collected specimens. except when populations are extremely vidual species can be characterized The adults emerge, usually from high or are concentrated on the buds by distinctive coloration and antennal late May until mid-July, and begin and flowers. Treatment is not recom- characteristics. to feed and lay eggs. Adults of each mended under normal conditions. blister beetle species emerge suc- Potatoes: Blister beetles can oc- Life cycle cessively during the growing season. cur in mid-summer on potatoes and Blister beetles lay eggs in clusters of Various blister beetle species may may cause extensive foliar damage. up to 100 in the soil. The eggs hatch be found in Montana from May until Typically, blister beetles may cause within 14 days into tiny, mobile lar- mid-September (Fig. 3). localized areas of foliage damage, vae, called triungulins, which move but widespread economic damage is about, searching for food. The im- Crop damage and economic rarely encountered. mature beetles feed on grasshopper impact egg pods or the larval cells of solitary Sugarbeets: Several species of blis- Risk posed by blister beetles bees, becoming increasingly sed- ter beetles feed on sugarbeet foliage in alfalfa hay entary as they feed. The larva over- and may cause isolated patches of Although adult beetles feed on al- winters in the soil in a specialized defoliation in the crop. Black, ash- falfa foliage, their primary impact form. In the spring, pupation occurs gray and spotted beetle species have is not due to defoliation damage. in response to increasing temperature been documented on sugarbeets in Instead, blister beetles are of concern and moisture. Blister beetles have Montana. However, economic infes- because they contain a toxin in their one generation per year. tations are rare. body fluids called cantharidin, a very

2 Figure 4. Major species that occur in Montana 3 stable compound. Blister beetles can can occur, kidney and heart function The risk of blister beetle poisoning be killed during hay harvest and in- can be impaired, and in severe cases, depends on how much cantharidin is corporated into baled forage. death can result. Horses are especially ingested. Several factors may effect When hay containing blister beetles prone to blister beetle poisoning, which the cantharidin concentration in the is ingested by sensitive livestock, blis- occurs when they feed on dried, baled baled forage including the species of tering of the esophagus and stomach forage containing the dried beetles. blister beetle, the beetle population

Species Adult length Coloring Season of Plants observed Damage (common name) emergence feeding on reported

Lytta cyanipennis 3/4 to 11/4 inch Head, thorax March to Au- Lupine, vetch, and wing cov- gust. In Mon- peas, alfalfa ers deep me- tana primarily and beans tallic blue vary- observed mid- ing to green June through mid-July

L. nuttalli 1/4 (Nutall) 3/4 to 1 inch Head and June and July Sweet clover, Reports of thorax usually alfalfa, milkvetch, damage to metallic green caragana, loco- canola, with wing weed and vetch barley, oats, covers canola, barley, beets and metallic oats, beets and sainfoin purple sainfoin

Epicauta fabricii 3/8 to 5/8 inch Uniformly ash June through Alfalfa, sweet clover, wild indigo, (ash gray) gray with black August soybeans and locoweed antennae

Epicauta ferruginea 1/4 to 1/2 Uniformly May through Canola, alfalfa, sunflower, thistle, inch golden in color August. gumweed and lentils

Epicauta maculata 1/2 to 1 inch Characteristic June (spotted) black spots through July caused by the absence of pubescence

Epicauta murina 1/4 to 3/8 Dark gray mid-June alfalfa inch to mid-August

Epicauta normalis 1/2 to 1 inch Gray with July unknown (dark) black spots (similar to E. maculata)

Epicauta pensylvanica 1/4 to 5/8 inch Uniformly June and July A wide range of plant hosts including (black) black crops such as alfalfa, sunflower, sugarbeets and weeds such as ama- ranthus, aster, nightshade, sage and yarrow

Epicauta sericans 1/4 to 3/8 Gray July Weeds, such as goldenrod, inch bindweed, nightshade

1 2

2 Table 1. Summary of research observations 3 and its distribution or density within tions have been documented to kill Sicklebar mowers, long recom- the field. Some species occur in horses. These species have not mended for reducing the potential very dense aggregations similar to been found to occur in Montana. for blister beetle incorporation into that of a honeybee swarm and these baled forage, were found to cause species have been most frequently Major species that occur in significant mortality if recently cut implicated in horse poisoning cases. Montana hay was driven over. Wheel traf- Aggregations of blister beetles oc- A survey of blister beetles in alfalfa fic on recently mowed alfalfa hay cur in localized areas of 100–200 was conducted during a 4-year study caused mortality of those beetles sq. ft. In this case, only a few flakes at Montana State University, 1994- remaining in the cut forage. Allow- from a bale of hay may contain 1997 by the authors. Eight species ing beetles to disperse after mow- blister beetles. However, the species were found to occur in Montana alfalfa ing and before baling reduced the that are known to cluster in swarms (Fig. 3). Blister beetle collection number of beetles incorporated into have not been found in Montana. information was also gathered from baled hay. The danger of blister beetles to for- the museum collection, Montana En- Insecticides can be used to re- age production is low in Montana. tomology Collection and used where duce populations. However, since host plant data are indicated. E. nor- blister beetles are mobile and may How many blister beetles malis was not found in field collec- move into the crop at any time, the can kill a horse tions, but specimens are present in residual activity of registered insec- Several factors contribute to the the Montana Entomology Collection. ticides may not be sufficient to con- severity of blister beetle poisoning, trol blister beetles up to harvest. including concentration of the toxin Management Another strategy would be to cantharidin, size and health of the Monitoring to detect the presence treat immediately before harvest, horse, and the dosage (or number of and type of blister beetle present is but insecticides with zero-day pre- beetles) consumed. John Capinera important. If blister beetles are pres- harvest intervals are not labeled for (formerly at Colorado State Univer- ent at harvest, it is important to use blister beetle control. Also, Kansas sity) did some work investigating harvest equipment that allows the State University discourages the the dosage of the toxin, cantharidin beetles to escape from mowed and use of insecticides because it causes (contained in blister beetles), need- swathed forage. Type of equipment beetle mortality, resulting in beetles ed to kill horses of different sizes. and its operation has an impact on remaining in the forage. The following table is taken from blister beetle mortality during hay Current insecticide recommend- work that he published. harvest. Research at Kansas State ations can be found in the High Although all blister beetle spe- University has shown that self-pro- Plains Integrated Pest Management cies contain some level of the toxin, pelled swathers without condition- Guide, located on the web at cantharidin, only those species ing rollers but with windrowing http://highplainsipm.org/ belonging to the ʻStripedʼ or Vittata attachments are safer than mower Group, that form dense aggrega- conditioners and sicklebar mowers. Summary The species that have been detected Cantharidin content beetles required to beetles required to in Montana are not regarded as a in beetle (mg) kill 550 lb horse kill 825 lb horse significant problem because num- 1 mg 250 beetles 350 beetles bers are relatively low and occur 3 mg 83 beetles 124 beetles infrequently. The species that is most frequently cited as the cause 5 mg 50 beetles 75 beetles of horse deaths have not been found Table 2. Cantharidin toxicity in horses (study by Capinera, CSU) to occur in Montana.

Copyright © 2002 MSU Extension Service We encourage the use of this document for nonprofit educational purposes. This document may be reprinted if no endorsement of a commercial product, service or company is stated or implied, and if appropriate credit is given to the author and the MSU Extension Service. To use these documents in electronic formats, permission must be sought from the Ag/Extension Communications Coordinator, Communications Services, 416 Culbertson Hall, Montana State University-Bozeman, Bozeman MT 59717; (406) 994-2721; e-mail - [email protected]. To order additional publications call your local county or reservation Extension office, or visit www.montana.edu/publications. The programs of the MSU Extension Service are available to all people File under regardless of race, creed, color, sex, disability or national origin. Issued Insects and Pests in furtherance of cooperative extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. B-20 (field crops) Department of Agriculture, David A. Bryant, Vice Provost and Director, Printed December, 2002 Extension Service, Montana State University, Bozeman MT 59717. 168-500-12-02-MG