Leafy Spurge Control Using Flea Beetles
(Aphthona spp.)
W-1183, December 1999 (Reviewed and reprinted
December 2002)
Rodney G. Lym, Professor, Department of Plant Sciences
Denise L. Olson, Assistant Professor, Department of Entomology
Introduction
Flea beetle life cycle
Where to release flea beetles
When to collect and release flea beetles
Limitations to biological control
Integrating biological control with other control methods
Leafy spurge is an exotic perennial weed that causes an
estimated annual economic loss of $23.2 million in North Dakota. Although leafy
spurge can be successfully controlled with herbicides, treating large acreages
is not cost-effective. In fact, approximately 40 percent of the leafy spurge
infested rangeland has a carrying capacity below the herbicide cost break-even
point. Using biological agents to control leafy spurge has become an economic
alternative in many locations in the state.
Biological control of leafy spurge was initiated in the mid 1980s. To date,
12 species of insects have been released in North Dakota for control of leafy
spurge, and eight have become established. Five of the eight established insects
are flea beetles, (Aphthona spp.) which have reduced the leafy spurge
density more than any other agent.
The first flea beetle released in North Dakota was Aphthona flava Guill
in 1986 (Figure 1). This flea beetle has established only at afew sites in the
state and occurs at densities too low to be effective. In 1988, a mixed population
of Aphthona czwalinae Weise and Aphthona lacertosa
Rosenhauer were released near Valley City, North Dakota. By 1995, the majority
(greater than 90 percent) of this mixed population was A. lacertosa and
will be referred to as such in this circular. Two additional flea beetles, Aphthona
cyparissiae Koch and Aphthona nigriscutis Foudras, were
released the following year. Aphthona abdominalis Duftschmid was
released in 1992 but has not yet contributed to leafy spurge control in the
state. A. lacertosa and A. nigriscutis were established
in almost every county in North Dakota by 1996 and have become the major biocontrol
agents used for leafy spurge control.
Figure 1. Aphthona species flea beetles are about the size of flax seed
(about 0.10 inches long) and vary in color and shape depending on species. Shown are:
- A. flava (copper to gold in color) (19KB
color photo)
- A. nigriscutis (brown with a black dot) (19KB
color photo)
- A. lacertosa (black with brown femurs) (27KB
color photo)
Flea beetle life cycle
Aphthona spp. adults emerge from the soil in late spring to early summer
(Figure 2). Following emergence, adults feed on leafy spurge leaf tissue and
mate. Females begin laying egg clusters of three to 15 eggs almost immediately.
Egg laying continues every three to five days throughout the adult life stage.
Aphthona spp. females produce an average of 220 to 280 eggs over a lifetime.
Eggs are yellow and laid on the soil surface or slightly below, near the leafy
spurge stem base. Larvae emerge from eggs in 12 to 19 days. The longevity of
A. czwalinae, A. lacertosa and A. nigriscutis will
vary from year to year depending on weather conditions. A hot, dry spring and
summer will shorten the time adults are present while a cool, wet season will
lengthen it. Generally, adults live for 1.5 to two months in the field. Most
leafy spurge flea beetles have a single generation, egg to adult, each year.
Figure 2. (3KB b&w diagram)
General flea beetle life cycle in North Dakota. All species except Aphthona adominalis
have one generation per year and over winter as larvae in the soil. A. adominalis
can average 3 to 4 generations per year, but has not yet established in the state.
Flea beetles undergo three larval instars. First- and second-instar larvae feed on
filamentous and larger leafy spurge roots, respectively. Third-instar larvae feed on the
root crown (Figure 3). Flea beetles overwinter as second- and third-instar larvae in the
soil. Larval feeding begins to decline when soil temperatures fall below 45 F and resume
feeding when soil temperature warms in the spring to above 45 F.
Figure 3. Larvae and holes from feeding damage in a leafy spurge root crown (click here - 27KB color photo), and
two larvae feeding in a leafy spurge root bud (click here -
22KB color photo).
Third-instar larvae feed for a number of weeks in early spring prior to pupation.
Larvae pupate away from the root and emerge as adults. Aphthona spp.
emerge in early to mid-June in North Dakota with the exception of A.
flava which emerges two to three weeks later. Peak emergence occurs first
in A. nigriscutis followed by A. lacertosa.
Although Aphthona spp. adults feed on leafy spurge foliage, the major damage to
the plant occurs when the larvae feed on the roots. Larvae feed on both the fine feeder
roots used by the plant to absorb water and nutrients and the storage tissue of the root
crown. This feeding both destroys root tissue directly and causes the plant to be more
susceptible to other methods of control, such as herbicides and infection from soil borne
pathogens.
Where to release flea beetles
Research at North Dakota State University found flea beetle establishment was best on
silt loam, silt clay loam, clay loam and clay soils with an organic matter content of 6 to
9.5 percent. Flea beetles were least productive in fine sand to loamy fine sand soils with
an organic matter content of 1 to 3 percent. In addition, the release area needs to be
well drained and not subject to frequent prolonged flooding or standing water, which will
kill the larvae.
Initial releases have been most successful on south-facing slopes, although
good success has been achieved on western and eastern slopes as well. On north
facing slopes, Aphthona spp. requires a longer period to establish at
high enough numbers to control leafy spurge. Flea beetles establish best in
moderate densities of leafy spurge (60 to 90 stems per square yard) with minimal
grass cover and thatch. Establishment in dense leafy spurge stands is often
difficult. Release flea beetles on the margins of dense infestations and allow
the insect to work into denser stands as the population builds.
Research data is lacking and/or has given inconsistent results concerning the
best species to release in a specific area. What is known at this time is that
A. lacertosa is more widely adopted to the North Dakota climate and will
tolerate a wider range of temperature and moisture conditions than other Aphthona
spp. A. nigriscutis generally has done better on higher, drier sites
with low to moderate stands of leafy spurge. Releasing a mixture of both species
in the same location is the best way to determine which Aphthona spp.
is best suited for a particular area.
When to collect and release flea beetles
Aphthona spp. flea beetles generally are distributed through the North
Dakota Weed Control Association. Contact the local county weed officer for date,
time, and location of flea beetle collection and redistribution programs in
your area. Flea beetles are generally collected and redistributed from mid-June
to early July. Total accumulated growing degree days (AGDD) for sunflower can
be used as a guide to determine when to begin scouting for adult flea beetles.
Begin scouting for adult flea beetles when the AGDD approaches 1,000 (Figure
4). Likewise, the flea beetle population and egg laying by females begins to
decline when the AGDD reaches 1,600 or more.
Figure 4. (4KB b&w graph)
Begin to scout and move adult flea beetles when the growing
degree days for sunflower approach 1,000 to 1,200. The peak emergence of Aphthona
spp. flea beetles also corresponds to the flowering of the prairie wild
rose and the ripening of garden strawberries in North Dakota.
Another method to determine when the flea beetle population is near peak abundance is
using plant phenology. Growth patterns by various plant species can be used as
`indicators' of seasonal abundance of leafy spurge flea beetles. Aphthona spp. are
often near peak levels when the prairie wild rose is flowering and strawberries are ready
to be picked in family gardens in North Dakota.
The best time to collect flea beetles for redistribution is from 10 a.m. to 3 p.m. when
the air temperature is greater than 70 F, there is little or no wind, and the skies are
generally sunny. Leafy spurge should be dry before collecting flea beetles because wet
conditions will make sweeping difficult and reduces the adult survival during
transportation.
To determine if a population has increased enough for redistribution, sweep five times
using a standard insect sweep net covering an area of 10 square feet and count the number
of flea beetles in the net (Figure 5). If flea beetles are too numerous to count
individually, remove excess trash and non-flea beetle insects and pour net contents into a
graduated container. Every 10 ml of flea beetles is approximately 1000 individuals.
Redistribute flea beetles to other leafy spurge infestations when 500 to 1000 beetles per
five minute sweeping period are collected. Over-harvest of beetles is not possible because
many flea beetles fall to the ground prior to being swept or are on the soil surface
laying eggs.
Figure 5. Sweep for Aphthona flea beetles on warm sunny days. The
sweeping motion should be in an arc from left to right over the top two thirds of the
leafy spurge plant. Avoid hitting rocks and soil. Figure A (50KB
color photo) Figure B (58KB color
photo)
Once collected, the flea beetles should be transported in paper bags or containers
(Figure 6). Do not use plastic containers because moisture condensing on the
plastic can drown the insects. Add some leafy spurge to the container and place
in a cooler containing blue ice. Do not allow the containers or cooler to sit
in the sun. Flea beetles should be released as soon as possible after collection.
Releasing the same day as collection is ideal; however, insects can survive
several days when refrigerated at 40 to 45 F. The more similar collection and
release environments are, the sooner the flea beetles are likely to become established
and begin to control leafy spurge.
Figure 6. Once Aphthona are collected, remove as much trash as possible
and place into paper cartons or bags. (Figure A - 24KB
color photo) Keep the containers in the shade and transport the insects in
coolers with blue ice. Flea beetle sorters may be used during mass redistributions.
Consult your local APHIS representative or weed control officer for availability. (Figure B - 24KB color photo)
At least 1,000 or more insects should be released per location. Often new populations
are started with several thousand insects (Figure 7). The higher the release
number, the faster a population increases. Do not scatter the adults over a
large area. Aphthona flea beetles are very gregarious, and males and
females need to be in close proximity. Multiple releases in a large area are
better than a single large release. Flea beetle establishment often increases
when release points are scattered over a wide area of terrain. It is important
to place a permanent marker such as a steel fence post at each release site
so the population can be monitored in subsequent years. Adult flea beetles are
susceptible to insecticides, so avoid wide-scale spraying near a flea beetle
population, especially from June through mid-August.
Figure 7. The larger the initial release number
of adult Aphthona flea beetles, the more likely the population will establish and
begin to control leafy spurge. (24KB color photo)
A successful release should result in 50 or more flea beetles in five sweeps,
the summer following release. If densities are less than 50 flea beetles per
five sweeps then re-infest the site with additional flea beetles of the same
and/or different species.
Although flea beetles have become established throughout North Dakota, they
have not been successful in all environments. To date, approximately 30 percent
of the releases have established and the leafy spurge stem density has been
reduced. In another 30 percent of the releases, the insects have become established
but the population density is too low to be effective. In the remaining releases,
flea beetles have not established.
If a flea beetle population becomes established but does not control leafy
spurge, perhaps a second release of the same and/or different species will improve
control. However, if the insect population does not increase after multiple
releases, the site may not be suitable for Aphthona spp. to control leafy
spurge. Each Aphthona spp. requires a slightly different type of habitat
for survival. Also, Aphthona spp. generally will not establish
at sites with excess moisture, long periods of shade, very sandy soil, high
leafy spurge density, or poor snow cover in the winter. Of these problems only
the density of the leafy spurge stand can be altered. Herbicide application
in the fall and sheep or goat grazing from mid-May until mid-August will reduce
the leafy spurge density and both methods are compatible with flea beetles.
Unlike herbicides, biological control agents do not provide predictable, consistent
levels of leafy spurge control. Often Aphthona spp. take several years to become
established and then require several more years to reduce a leafy spurge stand. Wide-scale
rapid reduction of leafy spurge infestations are so far the exception, not the rule.
Biological control of leafy spurge with flea beetles is not a "quick fix" and a
land manager must practice patience when using this control method.
Integrating biological control with other control methods
Several options are available for leafy spurge control besides biological control
agents, including the use of herbicides, grazing, seeding competitive grasses, and
cultivation. Before beginning a leafy spurge control program, consider the best options
suited for the situation and utilize more than one. Most successful control programs have
used multiple control methods combined over several years.
Herbicides should be used to control leafy spurge patches as they become established
and around the perimeter of larger infestations to keep them from spreading
while biological control agents become established. Research at North Dakota
State University has shown that a fall application of Tordon (picloram) plus
2,4-D at 1 quart plus 1 quart per acre ( 0.5 + 1 pound per acre) from early
September to mid-October on leafy spurge with an established flea beetle population
provided increased control compared to using either flea beetles or herbicides
alone. Also, herbicides applied to dense leafy spurge infestations will open
the canopy and may allow the biological control agents to establish in an otherwise
unsuitable environment.
Grazing by sheep or goats after mid-August can increase leafy spurge control
with Aphthona flea beetles. Grazing removes excess trash from
the soil surface, providing a more suitable environment for egg and larvae survival.
Fire may also be used to reduce cover, but avoid using a controlled burn until
after mid-August when egg laying has been completed.
Additional sources
- For more detailed information concerning IPM, biological, and other control methods for
leafy spurge consult the following references:
- Integrated Pest
Management of Leafy Spurge, NDSU Ext. Service Circular W-866R, 1995.
- Leafy Spurge
Identification and Control, NDSU Ext. Service Circular W-765R, 1998.
- Controlling Leafy
Spurge Using Goats and Sheep, NDSU Ext. Service Circular R-1093, 1995.
- Biological Control of Leafy Spurge, USDA-ARS TEAM Leafy Spurge, Sidney,
MT. Download at http://www.team.ars.usda.gov/
.
- How to Raise Leafy Spurge Flea Beetles, North Dakota Dept. of Ag, Bismarck, ND,
video.
- Photos 1a and 1b courtesy of Bob Richard, USDA-APHIS PPQ, Bozeman, MT, all
others are by Rodney G. Lym.
For more information on this and other topics, see:
http://www.ag.ndsu.nodak.edu
W-1183, December 1999 (Reviewed and reprinted
December 2002)
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