WESTERN BEAN CUTWORMS FLYING
We have finally begun to catch western bean cutworm moths in
our light trap at Concord.
This
is about 10 days after we usually see them, but coincides with where the
crop is developmentally.
Check
fields now for the egg masses.
See
Newsletter #10 for more information on the western bean cutworm.
GDD - WATER USE TABLES
We are finally beginning to include our growing degree day
water use tables in our hard copy.
We
apologize for the lateness in getting this started, since it is one of
the most popular features of the newsletter.
Remember, the tables are based on crop emergence date, which may
differ slightly for every field.
However,
at this time of year most of the water use will be very similar unless
the emergence dates are more than 2 weeks apart.
BLISTER
BEETLES NUMEROUS IN GARDENS, ALFALFA
Blister beetles are very common this year due to the fact that
the immature of the blister beetle feeds on grasshopper eggs.
Since grasshopper populations have been high
it is only logical that blister beetles will increase also.
They feed on a variety of plants but seem to
be enjoying potatoes and flowers in gardens.
However, they can be a serious problem to horses due to a toxin
(cantharidin) in their bodies.
The
following information is from
NebFact
NF02-551 by Jack Campbell, available in your local extension office.
Adult blister beetles (
Epicauta spp.) tend to be gregarious,
and several may be observed feeding on the same flowering plant such as
alfalfa or sometimes soybeans, goldenrod 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 (Fig. 1). 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.
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 numbers. Females deposit clusters
of eggs in depressions in the ground. Newly hatched larvae move through
the soil, feeding on grasshopper egg pods. They overwinter as a “pseudopupae”.
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 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. 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 poisoning.
Part or all of a horse's digestive tract can be severely irritated, leading
to secondary infections and bleeding. Cantharidin is absorbed and 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 lowers serum calcium levels and causes damage to heart
muscle tissue.
Researchers in 1985 conducted a cantharidin analysis on several
species of blister beetles commonly found in Colorado. They found differences
in amounts found among species 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. 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. However, 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, esophagitis, 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 (synchronous diaphragmatic flutter) associated
with the heartbeat. Poisoned horses may place the muzzle in water without
drinking, 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 veterinarian.
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 incorporated 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,
particularly 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 Entomology. 111. 4 pp.
Capinera, J.L., D.R. Gardner and F.R. Stermitz. 1985. Cantharidin levels
in blister beetles (Coleoptera: Meloidae) associated with alfalfa in Colorado.
Journal of Economic Entomology. 78: 1052-55. Gayle, L.G., J.C. Reagor,
A. Ray and E.M. Bailey. 1981. Cantharidin 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.
MANAGEMENT
TIPS
If
liquid manure is applied by sprinkler irrigation to a growing crop,
and if the electrical conductivity (EC) exceeds 3 mmho/cm, then
dilute it with fresh water. Sample the manure, and the mixture if
adding water, after pumping several hours. |
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