Biological Control
Agent: Aphthona nigriscutis Foundras
Invasive Plant Species Attacked: Leafy spurge
(Euphorbia esula) and cypress spurge (E. cyparissias)
Type of agent: Root feeding flea beetle
Status
Tertiary
Description and Biology
Adult:
Adults are brown coloured, oval shaped, and 3 - 4 mm long. Their unique feature,
the black gap at the top of the wing covers, distinguishes them from other Aphthona.
Adults begin to emerge in mid June through July and feed on the upper margins of leaves.
As with all Aphthona species, adults appear to congregate for feeding, mating and egg-laying.
Adults will breed almost immediately and begin to lay eggs within one week. Eggs are
deposited slightly underground near spurge roots in clusters of 20 to 30 every three to five
days. Each female will lay 200 - 300 eggs. Aphthona nigriscutis appears to
have a shorter oviposition period than A. cyparissiae. Intensive egg laying lasts
for two months before it slows over the next two months. This species remains high on
plants during warm summer days, often taking short flights. On warm days it avoids predation
by jumping readily, but, as temperatures drop to 10°C or less, they move less and
are more susceptible to animal grazing.
Egg:
Eggs measure 0.7 mm x 0.4 mm. During the 2 - 3 week incubation period, the pale coloured
eggs darken to brown-yellow.
Larva and pupa:
Elongated, white larvae with brown heads maintain a slight 'comma' or 'C' shape through
their three instars. Upon emergence, the first instar larvae feed together in small groups
in a parallel formation on the youngest roots, avoiding the latex producing layers. The
second and third instars no longer avoid the latex and feed on the outer tissue of
older roots and freely move between them. The feeding damage initiates new growth the
following year, causing the plant to send out new shoots from the attacked locations.
This is essential for the insect's survival. These new shoots provide an abundance of
young roots for larvae feeding the next year and may subsequently increase the adult population.
They will need to feed for about 100 days in an optimal climate to complete this portion of
their life cycle, larvae that fail to do so will stop development. Mature larvae will
leave the roots to prepare a soil particle pupation chamber. They must undergo a cold
period at 10°C or less (tolerating -7°C), for at least four months before
they resume development and pupate. Pupation occurs the following spring and takes 28
to 57 days to complete.
Overwintering stage:
Mature larvae overwinter in a prepared pupal chamber within the soil.
Location and effectiveness of attack
The larval stage is the main component of control as it feeds on the various roots, disabling
the plant's ability to absorb and store nutrients and moisture. This feeding will suppress
plant vigour and reproductive ability, delay flowering, and weaken or kill plants.
Adult foliar feeding is quite impressive as they can completely consume small and young
leaves, however, larvae provide the majority of control. Adults create "shot-hole" feeding
on leaves by scraping the upper leaf surface. Adults feeding on leaf tissues and new shoots
can impede photosynthesis, compounding nutrient starvation. Adults usually remain close to
the release location where the effects of attack will be apparent, but tend to disperse after
five years.
Visual impacts seen at established treatment sites:
- Reduced number of flowering stems;
- A temporary increase of short non-flowering stems is common, and will disappear after
about four years; and
- Native grasses replace the voids left from dead spurge.
Predicted and native habitat
A. nigriscutis is commonly found in bunch grassland habitat with needle and thread
grass. Preferred locations will have low density spurge (less than 60 stems/m²)
growing 70 cm tall. They prefer areas near the top of south facing slopes or on knolls
with well drained soils. Soil composition usually has 60% or more sand content with minimal
organic presence. Mortality increases as moisture levels increase. Optimal sites
are open, hot, dry locations where the plants suffer from drought stress during late July and
August. A climate with a 4-month period of temperatures of 10°C or less is required for
complete development. They will not compete well at locations where there are high ant
populations.
British Columbia Experiences
Origin:
A. nigriscutis population sources originate from Hungary. The
flea beetles were released in 1983 near Cardston, Alberta and reared to
collectable levels before they were shipped to BC.
History:
The first A. nigriscutis release in BC occurred in 1986 near Alexis Creek. In recent years
this site was revisited and the remaining leafy spurge is significantly reduced
and occurs as widely spaced individual plants. In 1994, a population mixed
with A. cyparissiae was released near Kamloops and flourished within three years. Several
thousand adults have been collected from this location for redistribution and today the site
has significantly less spurge. A. nigriscutis and A. cyparissiae
occur in mixed populations, dispersing freely in BC. Assisted
redistributions are ongoing and coincide with the pattern of the plants' growth
cycles.
Habitat:
A. nigriscutis has been released and found established into the
Bunchgrass, Interior Douglas-fir, Ponderosa pine and Sub-boreal spruce
biogeoclimatic zones.
Field results:
Past monitoring results found mixed A. nigriscutis /A. cyparissiae populations established and at most the release sites. It
is difficult to separate these two species and, therefore, it is acceptable to
consider them as mixed populations in field results. Adult populations drop significantly when the plants
become dried in August. When temperatures rise rapidly over a short period, adults become
harder to locate (adults found abundantly in 1998 disappeared quickly after several consecutive,
intensely hot days).
Sweep for adults through early summer on warm and hot days and aspirate to clean the collection.
During bright, hot days, adults rapidly rise on plants, allowing for repeat sweeping. Sites
are usually harvestable by three years following treatment.
Literature sources indicate, new treatments provide earlier results when large numbers
are released. When treatments are made with small numbers, the resulting populations tend to
persist with small numbers, never showing a significant upward surge in population.
Notes
A. nigriscutis and A. cyparissiae habitats overlap and are visually similar,
making identification between the two difficult.
References
Harris, P. 1994. Biological control of leafy spurge on the prairies. Leafy Spurge News.
Vol. XVI, Issue 3: 2.
Harris, P. 2006. Classical biological control of weeds. Established biocontrol agent Aphthona
nigriscutis Foudras. Root beetle. Agriculture and Agri-Food Canada. December 8, 2006.
http://res2.agr.ca/lethbridge/weedbio/agents/aaphtnig_e.htm
Mason, P. G. and J. T. Huber, (editors). 2002. Biological control
programmes in Canada, 1981 - 2000. CAB International.
MFR staff observations and comments.
Powell, G. W., A. Sturko, B. Wikeem and P. Harris. 1994. Field guide to the biological
control of weeds in British Columbia. B.C. Min. For. Res. Prog.
Saskatchewan Agriculture and Food and Saskatchewan Rural Development. No date. Biological
control of leafy spurge. Farm Facts. Gov. of Can. 3 p.
Spencer, N. R. 1997. Niche specificity of insects introduced for leafy spurge control.
Leafy Spurge News. Vol. XIX, Issue 1: 8.
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