Grasshoppers
Phillip A. Glogoza, Extension
Entomologist
Michael J. Weiss, Professor of Entomology
Each season grasshoppers are a
threat to field crops, forage crops, pastures and rangeland..
The most severe infestations are
likely to occur during seasons when the weather is hot and
dry.
Scouting should begin in May and
early June, and producers should be prepared to start management
measures when young hopper populations reach threatening
levels.
Grasshopper eggs are laid beneath
the soil surface in pod-like structures that the female
deposits from her abdomen. Each egg pod consists of 20 to
120 elongated eggs securely cemented together; the whole
mass is somewhat egg shaped and covered with soil. A female
grasshopper produces from eight to 25 egg masses. The species
of grasshoppers that cause major crop loss overwinter in
the egg stage, although a few other
noneconomic species overwinter as nymphs.
In the Northern States, grasshopper
egg hatch normally begins in late April to early May. The
peak hatch occurs about mid June and the hatch is usually
nearing completion by late June. Cool and extremely dry
springs may delay the hatch, allowing it to continue into
July.
Young grasshoppers are referred to
as nymphs. They are similar to adults in general appearance
but are smaller and have wing pads instead of wings. There
are usually five or six nymphal stages and the length of
time from egg to adult is 40 to 60 days. Knowledge of grasshopper
instar identification is useful because it gives a rough
indication of how far the hatch has progressed.
Normally, once fourth and fifth instar
grasshoppers are present, the hatch is winding down. More
important, recognition of fifth instar hoppers indicates
that the winged adult stage is soon to follow. Winged adults
are much more mobile than the nymphal stages. Wingpads of
first to third instar hoppers are borne saddle-like over
the thorax. Wingpads of fourth and fifth instar hoppers
are pointed backward over the abdomen and differ only in
size. In the fourth instar they are relatively small and
extend only to the first abdominal segment, while in the
fifth instar they are large and extend past the second abdominal
segment.
Adults of crop-damaging grasshopper
species become numerous in mid July with egg laying activity
usually beginning in late July and continuing into fall.
Eggs are deposited in a variety of non-crop areas including
ditches, fence rows, shelterbelts and weedy areas. They
are also laid in cropped areas including late season crops,
weedy fallow fields and headlands as well as in haylands
and alfalfa. Migratory and clear winged grasshoppers frequently
lay eggs in pastureland.
Weather is the main factor affecting
grasshopper population levels. Outbreaks are usually preceded
by several years of hot, dry summers and warm falls, allowing
populations to increase slowly.
|
How weather affects grasshoppers
|
Temperature Effects
- High temperatures
in summer - fall
Early
maturity of grasshoppers
Long egg laying period
- Warm spring
Early hatch, followed by:
<70o -->No feeding, high mortality
Warm and dry --> Good start for
hoppers
- Winter temperatures
have little affect
|
Rainfall Effects
- Cloudy, wet weather
for 1+ weeks
Promotes
fungal pathogens
of
grasshoppers
Prolonged
wet period important
- Heavy rains during
emergence
Kills
young grasshoppers
embeds young hoppers in soil
physically wash them away
- Extreme drought
Poor egg hatch
Hoppers
starve from lack of food
Low egg production by adults
|
|
Weather effects and their impact on
grasshopper populations
|
Decrease when . .
.
- Warm early spring
premature hatch
IF get a cold snap --> poor
development
- Hot period in early
spring...
promotes hatching
...following
by cloudy, wet weather
favors the occurrence of disease
- Cool summer and early
fall
delays the maturity of the
grasshoppers
shortens the time for egg laying
|
Increase when . .
.
- Cool, wet weather
in early spring
prevents premature hatch
insures adequate food supply
- Warm and dry in late
spring
promotes uniform hatching time
good weather conditions for
feeding
- Hot summer with adequate
rainfall
provides good food supply
low incidence of disease
- Late fall
long egg laying period
|
Grasshopper damage to wheat and other
cereal crops is generally concentrated near field margins.
Individual plants will exhibit leaf stripping, beard loss
after heading, head clipping, and kernels that have been
fed upon or completely destroyed. When grasshopper populations
are extremely high and food plants are scarce, grasshoppers
migrate and will consume almost any plant they come upon.
Row crop producers should be aware of the potential for
grasshoppers to move into row crops after small grains have
begun to dry down.
BACK TO TOP
Grubs
Knowing the life cycle of grubs is the key to determining
whether you have a problem, what to do about it, and when
to do it. A white grub is the immature (larval) form of
a scarab beetle, such as a European chafer or Japanese beetle.
Grubs live in the soil, feeding on plant roots, so you may
not be aware of them until you see damage. By considering
a grub’s life cycle, you can anticipate problems before
your lawn is ruined. The biology of the Japanese beetle
is typical of most grubs encountered in New York State and
is explained below.
European chafer beetle (adult)
Adult Japanese beetle
|
Life cycle of Japanese beetle.
|
A. In late June and early July, Japanese beetle
adults emerge from the ground and begin to search for food
and mates. The adults can fly as far as a mile and feed
on a multitude of plants; their favorites include roses,
grapes, and linden trees. Other scarab beetles may go unnoticed
at this time because they are not attacking ornamental plants.
B. In July, female beetles spend 2–3 weeks laying
up to 60 eggs in the soil. Depending on soil moisture and
temperature, eggs hatch about 2 weeks later. These first-stage
("first-instar ") grubs feed on grass roots for most of
August. The grubs are small, feeding close to the surface,
and vulnerable to biological and chemical insecticides at
this time. Control high populations at this stage, before
feeding on turf roots is noticeable.
Eggs and newly hatched grubs of Japanese beetle.
|
Grub larva, third stage (instar)
|
Pupa (becoming an adult)
|
C. From late August through October (depending
on your climate), grubs molt into a second and then a third
stage. As they grow, grubs consume more roots. Damaged turf
often appears now.
D. As temperatures drop in autumn, grubs move
down in the soil. They overwinter as third-instar grubs
below the frost line.
E. In the spring, they move up in the soil to
feed on roots for a very short time. (Most of the lawn damage
seen in the spring is a result of fall feeding, not spring
feeding.)
F. In late spring, grubs stop feeding and turn
into pupae that are resistant to insecticides. In late June
or early July, beetles emerge from the pupae and crawl out
of the soil, completing the cycle.
THE GRUB-DAMAGED LAWN
Severe grub damage in a lawn appears as large, irregular
sections of brown turf that detach from the soil without
effort. Unlike turf damaged by drought or excessive fertilizer,
the turf peels away like a carpet being rolled up.
For most of the year, however, grubs are out of sight
and out of mind. They feed on grass roots in your lawn and
are usually noticed only when dead and damaged areas appear.
BACK TO TOP
Green June Beetle
The green June beetle is in the
Scarabaieidae family and also referred to as white
grubs. Unlike many of the other white grub pest of turfgrass
this species is unique in that it will come to the soil
surface and crawl on the turfgrass at night. Their larval
tunneling activity can damage turfgrass stands.
Identification
The adult green June beetle is
usually 3/4" to 1" long, and 1/2" wide. The top side is
forest green, with or without lengthwise
tan stripes on the wings. The underside is metallic bright
green or gold, bearing legs with stout spines to aid in
digging. In the Mid-Atlantic region the names "June bug"
and "June beetle" are commonly used for this insect. They're
called "fig eater" in the southern part of their range.
Do not confuse the green June beetle, however, with the
familiar brown May or June beetles that are seen flying
to lights on summer nights. The green June beetle adult
flies only during the day.
The larvae are white grubs often
called "Richworms" because they prefer "high" levels of
organic matter for food. With three growth stages they develop
and are similar to the other annual scarab species. Their
body lengths reach 1/4", 3/4", and 2" respectively. The
larvae have stiff abdominal bristles, short stubby legs,
and wide body. One unique characteristic of this grub is
that it crawls on its back by undulating and utilizing its
abdominal bristles to gain traction. Other typical white
grubs, like the Japanese beetle grub, are narrower, have
longer legs, crawl right side up and when at rest assume
a "C" shaped posture.
The most closely related U. S.
species is Cotinis mutablis.
Distribution
This species is native to the
eastern half of the United States and overlaps with
Cotinis mutablis in Texas and the southwestern
United States.
Hosts
The adults generally don't
feed but occasionally become a pest of fruit. Any thin
skin fruit such as fig, peach, plum, blackberry, grape
and apricot can be eaten. The principal attraction is
probably the moisture and the fermenting sugars of ripening
fruit. They occasionally feed on plant sap. In turf
situations egg laying females are attracted to moist
sandy soils with high levels of organic matter. Turf
areas treated repeatedly with organic fertilizers, composts
or composted sewage sludge become more attractive to
the female.
The grub feeds on dead, decaying
organic matter as well as plant roots. This species
is commonly associated with both agricultural crop and
livestock production areas as well as urban landscapes.
Field stored hay bales, manure piles, grass clipping
piles, bark mulches and other sources of plant material
that come in contact with moist soil are prime microhabitats
preferred by both the female for egg laying and the
migrating 3rd instar grubs
Life Cycle
The green June beetle completes
one generation each year. Adults begin flying in June
and may continue sporadically into September. The peak
occurrence of adults is during a two week period in
mid-July in Maryland and Virginia. On warm sunny days,
adults may swarm over open grassy areas. Their flight
behavior and sounds resembles that of a bumble bee.
At night they rest in trees or beneath the thatch.
The adult females shortly after
emerging may fly to the lower limbs of trees and shrubs
and release a pheromone that attracts large numbers
of males. Frequently, males repeatedly fly low and erratic
over the turf trying to locate emerging females. After
mating, females burrow 2" to 8" into the soil to lay
about twenty eggs at a time. The spherical eggs are
white and almost 1/16" in diameter.
Most eggs hatch in late July
and August. The first two instar stages feed at the
soil thatch interface. By the end of September, most
are third instar larvae and these large grubs tunnel
into the thatch layer and construct a deep vertical
burrow. The grubs may remain active into November in
the Mid-Atlantic region. In the more southern states
grubs may become active on warm nights throughout the
winter. In colder areas they overwinter in burrows 8"-30"
deep. The grubs resume feeding once the ground warms
in the spring and pupate in late May or early June.
The adults begin emerging about three weeks later.
BACK TO TOP
Leafhoppers
Leafhoppers are one of the largest families of plant-feeding
insects. There are more leafhopper species worldwide
than all species of birds, mammals, reptiles, and amphibians
combined. Leafhoppers feed by sucking the sap of vascular
plants, and are found almost anywhere such plants occur,
from tropical rainforests, to arctic tundra. Several
leafhopper species are important agricultural pests.
Details of the life cycle vary from species to species.
In general, the female inserts several eggs into the living
tissue of the host plant. The eggs either remain dormant
for a period ranging from a month to over a year, or develop
and hatch
 within
a few weeks. The young, known as nymphs, feed on plant sap
by inserting their beaks into the vascular or parenchyma
tissues of the host plant and go through a series of five
moults (shedding their exoskeleton), reaching the adult
stage after a period of several weeks or months. Adult males
and females seek each other out for mating, locating each
other through specialized courtship calls.
All feed on plant sap. Leafhopper species feed on a wide
variety of vascular plant species, including grasses, sedges,
broad-leafed woody and herbaceous plants of many families,
and conifers. At least one leafhopper species can usually
be found feeding on the each of the dominant plant species
in practically every terrestrial ecosystem. Frequently several
leafhopper species can be found coexisting on the same plant.
Nationwide, the potato leafhopper is a very injurious
pest of forages, particularly alfalfa and clover. Both nymphs
and adults feed on the undersides of the leaves. By extracting
the sap, they cause stunting and leaf curl, as well as the
condition called "hopperburn." This disease is caused by
the injection of a toxic substance. It is characterized
by a yellowing of the tissue at the tip and around the leaf
margin which increases until the leaf dies. Symptoms are
sometimes confused with drought stress.
BACK TO TOP
Spittlebug
The Saratoga spittlebug, Aphrophora saratogensis
(Fitch)2, so called because it was first collected
in Saratoga
County, N. Y., is a native insect that is destructive to
several species of pine in Eastern North America. It occurs
where ever its host grows, from Maine to Minnesota in the
United States and in the southern portions of the adjacent
Canadian Provinces.
The adult of this insect often destroys young pines,
especially in plantations where its alternate hosts are
abundant. Natural-grown and large trees usually are less
injured.
Hosts
 |
| Figure 1 - Sweet-fern
plant-the principal host of the spittlebug nymph. |
Red pine is the preferred host of the adult spittlebug.
Jack pine follows, although decreased planting of this species
in recent years has lessened its importance as a host. Scots
pine, which is increasingly planted for Christmas trees,
is occasionally injured by the spittlebug.
White pine is frequently fed upon but seldom damaged
severely. Adult spittlebugs thought to be Aphrophora
saratogensis have been collected from pitch pine, tamarack,
balsam fir, and northern white-cedar-usually from trees
near infested red pine. The nymphs require two alternate
hosts for their development. The early stages or instars
feed on herbaceous species of plants of the forest floor
such as brambles (raspberry and blackberry), orange hawkweed,
everlasting, aster, and many others. Older nymphs feed on
sweet-fern (fig. 1) and willow sprouts.
Damage
 |
| Figure 2 - Red pine
showing flagging symptoms from adult spittlebug
feeding. |
Young trees between 0.6 m and 4.6 m (2 and 15 ft) tall are
injured by the adult spittlebug attack. The first symptoms
of injury are one or more reddish or reddish-brown (flagged)
branches in the upper crown (fig. 2).
Scraping the outer bark from the 2-year-old internodes
of the flagged branches will reveal tan or brown flecks
on the surface of the wood and inner bark (fig. 3), which
confirms the injury caused by this spittlebug. These are
puncture wounds or scars that develop at the location of
adult feeding. If these puncture wounds are numerous, the
nutrient transport in the branches is restricted and the
branches die, resulting in the flagging symptom.
Continued heavy feeding results in increased flagging,
top kill, stem deformity, and tree death. The worst injury
always occurs where there are abundant alternate hosts for
the nymphs.
 |
Figure 3 - Puncture
wounds caused by adult spittlebugs feeding on wood
of pine host. |
Description
The egg is about 2 mm (0.08 in) long and teardrop shaped.
When freshly laid in summer it is glistening yellow. After
overwintering it is purple with a reddish spot.
The first four nymphal stages, which are found in spittlemasses
on the alternate host plants, have have bright scarlet abdomens
bordered by black at the sides and jet black heads and bodies.
The fifth stage nymph is dark brown.
The adult is a winged, boat-shaped insect (see cover
photo) about 8 mm (0.3 in) long. It is tan with whitish
markings, which makes it difficult to see against the buds
or bark of its hosts. The female is slightly larger than
the male and is distinguished by its swordlike ovipositor.
This spittlebug can be readily distinguished from related
species by a white arrow-shaped marking on top of the head
and body.
Life History and Habits
The spittlebug has one generation each year. On red pine
the eggs are laid under the outer scales of buds in the
upper branches. Several eggs are usually laid in each bud
causing noticeable bumps on the outer surface of the bud.
On jack pine the eggs are laid in the needle sheaths; apparently
the buds are too hard and resinous.
Nymphs hatch from the eggs in early May, drop to the
ground, seek out alternate host plants, and feed. As they
feed they form a spittlemass, which prevents desiccation
and protects them from enemies. The young nymphs feed on
several species of plants; older nymphs congregate on sweet-fern
and up to 50 may inhabit a large "community" spittlemass.
In late June or early July, when full grown, the nymphs
leave the spittlemasses, climb up the alternate hosts, and
shed their skin to become adults. Adults fly to the pine
hosts and feed on the sap of the branches until the end
of September. Most of the feeding injury occurs from mid-July
to mid-August. Mating occurs soon after transformation to
the adult stage, and egg laying begins within a few days.
BACK TO TOP
Sod Webworm
David J. Shetlar
There are several species of caterpillars called sod
webworms that can be highly destructive pests of lawns.
They may also become important pests of grass covered parks,
cemeteries, golf courses. They have even been noted to cause
damage in small grain crops such as corn, wheat and oats.
Damage to grass is caused by the feeding of the larval or
"worm" stage. The adult moth does not cause damage to turf,
other plants or clothing.
The damage caused by sod webworms may first appear in
early spring. The damage shows up as small dead patches
of grass among the normally growing grass. The summer generation
may cause general turf thinning or even irregular dead patches
in late June into early August. Sod webworms prefer sunny
areas and the larvae are often found on south facing, steep
slopes and banks, where it is hot and dry. Heavily shaded
turf is seldom attacked by the larvae.
The most severe damage usually shows up in July and August
when the temperature is hot and the grass is not growing
vigorously. In fact, most sod webworm damage is mistaken
for heat and drought stress. Sod webworm-damaged lawns may
recover slowly, without irrigation and light fertilizations.
These thin turf areas allow weeds to establish in the lawn
making it unsightly.
Turfgrass Attacked
Sod webworms appear to feed on all the common turfgrass.
However, common Kentucky bluegrass, perennial ryegrass and
fine fescues are the ones showing damage the most. However,
improved perennial ryegrasses with endophytes are highly
resistant to sod webworms. Likewise, tall fescue, though
often attacked, usually out grows the damage. On golf courses,
bentgrasses are commonly attacked.
Recognizing Sod Webworm Injury
The general thinning of turf is usually not associated
with sod webworm activity, and thus, goes undiagnosed. The
sod webworm caterpillars live in tunnels constructed in
turf thatch or extending to the soil under the turf. These
tunnels are silk lined and the webbing joins soil particles
and leaves together. The larvae emerge from these burrows
to chew grass blades off just above the thatch line, usually
at night.
In thick, green turf, injury appears as small brown patches
about the size of a quarter to three inches in diameter.
When many larvae are present in mid-summer, the small brown
patches run together and form large irregular, thin and
brown areas.
Confirming Sod Webworm Activity
The surest way to tell if you have sod webworms is to
find a suspected area of infestation (brown patches). Get
down on your hands and knees, take your two index fingers
and part the grass blades in the area between dead and live
grass and look for an area with small green pellets. The
pellets, called frass, are the excrement of the larvae and
indicate that a larva is close by. Sod webworm adults are
about 3/4-inch long, cigar-shaped and buff-colored moths.
They typically roll their wings around the body when resting
on a grass blade. Two small snout-like projections are visible
at the front of the head.
The adult moths fly mainly in late June and again in
mid-August though some species may be present any time during
the summer. Seeing these moths fly up while mowing or walking
around the lawn does not confirm that damage is, or will
be done by the larvae. The adult moths can fly considerable
distances and may be coming from other infested areas.
If you still suspect sod webworm activity but are unable
to find the larvae or their frass, use a soap disclosing
drench. Simply mix up two gallons of tap water with two
tablespoons of liquid dishwashing detergent. Sprinkle this
mix over a one square yard of the affected turf. Within
a couple of minutes, the flesh-colored, spotted larvae will
wriggle to the surface. If you get 10 to 15 larvae in a
one square yard of turf, treatment is warranted.
BACK TO TOP
VOLES
Identification
Voles, also called meadow mice or field mice, belong
to the genus Microtus. Voles are compact rodents with stocky
bodies, short legs, and short tails. Their eyes are small
and their ears partially hidden. Their underfur is generally
dense and covered with thicker, longer guard hairs. They
usually are brown or gray, though many color variations
exist.
There are 23 vole species in the United States. This
page provides range maps, descriptions, and habitat characteristics
for seven species that are widespread or cause significant
economic damage. Tentative identification of a particular
animal may be made using this information. For positive
identification, use a field guide or contact an expert.
Prairie Vole (Microtus ochrogaster). The prairie
vole is 5 to 7 inches (13 to 18 cm) in total length (nose
to tip of tail). Its fur is gray to dark brown and mixed
with gray, yellow, or hazel-tipped hairs, giving it a “peppery”
appearance. Underparts are gray to yellow-gray. It is the
most common vole in prairie habitats.
Meadow Vole (M. pennsylvanicus). The meadow
vole is the most widely distributed Microtus species in
the United States. Its total length is 5 1/2 to 7 1/2 inches
(14 to 19 cm) and its fur is gray to yellow-brown, obscured
by black-tipped hairs. Northern subspecies may also have
some red in their fur. Its underparts are gray, at times
washed with silver or buff. The tail is bicolored.
Long-tailed Vole (M. longicaudus). The long-tailed
vole can be distinguished from other Microtus species by
its tail, which comprises 30% or more of its total length
of 6 to 8 1/2 inches (15 to 21 cm). The long-tailed vole
has gray to dark brown fur with many black-tipped hairs.
The underparts are gray mixed with some white or yellow.
The tail is indistinctly to sharply bicolored.
Pine or Woodland Vole (M. pinetorum). The pine
vole is a small vole. Its total length is 4 to 6 inches
(10 to 15 cm). Its brown fur is soft and dense. The underparts
are gray mixed with some yellow to cinnamon. The tail is
barely bicolored or unicolored.
Montane (or Mountain) Vole (M. montanus). The
montane vole is 5 1/2 to 8 1/2 inches (15 to 20 cm) in total
length. Its fur is brown, washed with gray or yellow, and
mixed with some black-tipped hairs. Its feet are usually
silver-gray and its body underparts are whitish. The tail
is bicolored.
Oregon Vole (M. oregoni). The Oregon vole is
5 1/2 to 6 1/2 inches (14 to 16 cm) in length. Its fur is
gray to brown or yellow-brown. Underparts are darkish, washed
with yellow to white. The tail is indistinctly bicolored.
California Vole (M. californicus). The California
vole is 6 to 8 1/2 inches (15 to 20 cm) in total length.
Its fur is tawny olive to cinnamon brown with brown to black
overhairs. The underparts are grayish. The tail is bicolored.
Range
Figures 2, 3, 4, and 5 show the approximate ranges of
these species.
 Habitat
Voles occupy a wide variety of habitats. They prefer
areas with heavy ground cover of grasses, grasslike plants,
or litter. When two species are found together in an area,
they usually occupy different habitats. Though voles evolved
in “natural” habitats, they also use habitats modified by
humans, such as orchards, windbreaks, and cultivated fields,
especially when vole populations are high. Characteristic
habitat descriptions for the seven described species follow.
Prairie Vole. The prairie vole, as the
name suggests, is the most common vole of the Great Plains
grasslands. It is found in a variety of habitats, such as
old fields, marshlands, and grass prairies. When in association
with the meadow vole, it is generally in drier habitats.
Meadow Vole. The meadow vole is found
in the northern United States and Canada. It prefers wet
meadows and grassland habitats. When in association with
the montane vole or prairie vole, it is generally in moister
habitats.
Long-tailed Vole. The long-tailed vole
is found in a wide variety of habitats (for example, sagebrush
grasslands, forests, mountain meadows, and stream banks)
in the western United States and Canada.
Pine Vole. The pine vole is found in
the eastern United States. It inhabits a variety of habitats
such as deciduous and pine forests, abandoned fields, and
orchards. Heavy ground cover is characteristic of these
habitats.
Montane Vole. The montane vole is found
primarily in mountainous regions of the western United States.
It is found in alpine meadows, dry grasslands, and sagebrush
grasslands. It avoids forests. When in association with
the meadow vole, it is generally in drier habitats.
Oregon Vole. The Oregon vole is most
often found in forested areas of northern California, Oregon,
and Washington where there is an understory of forbs and
grasses such as in burned or clear-cut areas.
California Vole. The California vole
inhabits the chaparral woodland shrubland of California.
It is found in both wet and well-drained areas.
Food Habits
Voles eat a wide variety of plants, most frequently grasses
and forbs. In late summer and fall, they store seeds, tubers,
bulbs, and rhizomes. They eat bark at times, primarily in
fall and winter, and will eat crops, especially when their
populations are high. Occasional food items include snails,
insects, and animal remains.
General Biology, Reproduction, and Behavior
Voles are active day and night, year-round. They do not
hibernate. Home range is usually 1/4 acre (0.1 ha) or less
but varies with season, population density, habitat, food
supply, and other factors. Voles are semifossorial and construct
many tunnels and surface runways with numerous burrow entrances.
A single burrow system may contain several adults and young.
Voles may breed throughout the year, but most commonly
in spring and summer. In the field, they have 1 to 5 litters
per year. They have produced up to 17 litters per year in
a laboratory. Litter sizes range from 1 to 11, but usually
average 3 to 6. The gestation period is about 21 days. Young
are weaned by the time they are 21 days old, and females
mature in 35 to 40 days. Life spans are short, probably
ranging from 2 to 16 months. In one population, there was
88% mortality during the first month of life.
Large population fluctuations are characteristic of voles.
Population levels generally peak every 2 to 5 years; however,
these cycles are not predictable. Occasionally during population
irruptions, extremely high vole densities are reached. Dispersal,
food quality, climate, predation, physiological stress,
and genetics have been shown to influence population levels.
Other factors probably also play a part.
Many voles are excellent swimmers. The water vole, in
fact, escapes predators by swimming and diving. The climbing
ability of voles varies. The long-tailed vole, for example,
is a good climber (Johnson and Johnson 1982) while the pine
vole is a bit clumsy in this regard.
Voles are prey for many predators (for example, coyotes,
snakes, hawks, owls, and weasels); however, predators do
not normally control vole populations.
Damage and Damage Identification
Voles may cause extensive damage to orchards, ornamentals,
and tree plantings due to their girdling of seedlings and
mature trees. Girdling damage usually occurs in fall and
winter. Field crops (for example, alfalfa, clover, grain,
potatoes, and sugar beets) may be damaged or completely
destroyed by voles. Voles eat crops and also damage them
when they build extensive runway and tunnel systems. These
systems interfere with crop irrigation by displacing water
and causing levees and checks to wash out. Voles also can
ruin lawns, golf courses, and ground covers.
Girdling and gnaw marks alone are not necessarily indicative
of the presence of voles, since other animals, such as rabbits,
may cause similar damage. Vole girdling can be differentiated
from girdling by other animals by the non-uniform gnaw marks.
They occur at various angles and in irregular patches. Marks
are about 1/8 inch (0.3 cm) wide, 3/8 inch (1.0 cm) long,
and 1/16 inch (0.2 cm) or more deep. Rabbit gnaw marks are
larger and not distinct. Rabbits neatly clip branches with
oblique clean cuts. Examine girdling damage and accompanying
signs (feces, tracks, and burrow systems) to identify the
animal causing the damage.
The most easily identifiable sign of voles is an extensive
surface runway system with numerous burrow opening . Runways
are 1 to 2 inches (2.5 to 5 cm) in width. Vegetation near
well-traveled runways may be clipped close to the ground.
Feces and small pieces of vegetation are found in the runways.
The pine vole does not use surface runways. It builds
an extensive system of underground tunnels. The surface
runways of long-tailed voles are not as extensive as those
of most other voles.
Voles pose no major public health hazard because of their
infrequent contact with humans; however, they are capable
of carrying disease organisms, such as plague (Yersinia
pestis) and tularemia (Francisilla tularensis).
Be careful and use protective clothing when handling voles.
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The
Deer Tick, Ixodes dammini, is the vector for
Lyme disease in the northeastern United States, primarily
because this tick has
been most extensively studied. There is ongoing debate
whether I. dammini is conspecific with I. scapularis,
the member of the I. ricinus complex present in the
southeastern United States. What is clear is that the
northern tick population poses a much
greater threat of transmitting Lyme disease. Possible
explanations for the apparent increase in the population
of I. dammini and the expansion of its geographic range
are reviewed, as is the impact of changing patterns
of land use in the United States over the past century,
which have created environments ideally suited for ticks
and deer (the preferred host for adult I. dammini ticks)
and which bring humans into close proximity to both.
An
important concept (albeit relatively simple) is that
the total population of ticks in a region is a result
of the balance among fecundity (the number of offspring
produced per female), mortality, and migration. The
maximal number of offspring per adult female tick is
estimated to be approximately 3000.
Possible
techniques of environmental management to reduce the
risk of the disorder will require IPM. Options discussed
include measures for personal protection as well as
environmental measures, including "habitat modification"
(e.g., burning underbrush), "host exclusion" (e.g.,
deer fencing), and both "off-host" methods (e.g., insecticides)
and"on-host" options to increase tick mortality. Several
possibilities of particular scientific interest are
distributing insecticide-impregnated cotton balls in
the environment where mice (important hosts forimmature
I. dammini ticks) may use them in nesting material;
developing vaccines against tick saliva to promote rejection
of the tick during feeding, thereby preventing engorgement,
particularly of adults feeding on deer, and thus interrupting
the tick's life cycle before mating; and developing
mixtures of pheromones with acaricides. Pheromones are
chemical compounds produced by ticks as chemical signals
to facilitate communication. Some pheromones are attractants
(for example, sex pheromones); they could be tagged
with tick insecticide (acaricide), thus increasing its
power.
It
is highly likely that the successful control of Lyme
disease will require an integrated management approach
that will include personal-protection measures, improved
diagnostic and therapeutic approaches, and environmental
interventions at many levels.
In
this era of increased consciousness of the costs of
public health as well as those of individual health
care, interventions must be chosen with attention to
what is most likely to reduce the risk of Lyme disease.