Biological Control Agent: Aphthona lacertosa (Rosh.)
Invasive Plant Species Attacked: Leafy spurge
(Euphorbia esula) and cypress spurge (E. cyparissias)
Type of agent: Root feeding flea-beetle
Status
Primary
Description and Biology
Adult:
Aphthona lacertosa bodies are black and 2.5 - 3.4 mm long and are equally tapered
throughout. The upper part of their rear legs are brown, making it only slightly different
than A. czwalinae and difficult to tell them apart. Emerging adults appear in early
June, usually 10 days before A. czwalinae , and continue into mid August.
Females lay eggs in small batches at the base of leafy spurge stems. Each female lays
200-300 eggs during their six to eight week oviposition period. As with all flea-beetles,
it too is capable of jumping great distances and does so readily. It is considered the
most active of all the Aphthona species. Adults adjust to temperature by seeking
sun on cold days and moving to shade or onto lower plant leaves during hot days. Some
populations have short wings, while others do not; there is no explanation for this.
Adults can live up to two months.
Egg:
Eggs are pale yellow and measure 0.7 x 0.4 mm.
Larva and pupa:
Larvae are white and slender with brown heads and often in a comma-like position.
The first instar begins to mine latex-free fibrous roots and later instars move onto the outside
layer of older roots. Once the larvae have finished feeding, they leave the roots and
move into the soil to prepare to pupal cell. Mature larvae require a 4-month cold period
to initiate further development. Late hatchings that encounter the cold temperatures
before they feed sufficiently will survive the winter, but, will not go on to reproduce.
Pupation occurs the following year and is completed by the end of spring or early summer.
Overwintering stage:
Mature larvae overwinter in a pupal cell in the soil.
Location and effectiveness of attack
Larvae feed on fibrous roots before moving onto the mature roots. The larvae appear
to concentrate on specific plants resulting in plant death and reducing the plant density as
opposed to retarding the plant vigour. High concentrations can cause what is called a
'hole in the spurge', where the plants become noticeably reduced.
Adults feed on leaves, terminals, margins and shoots. In dense populations, adult
feeding is quite impressive and can defoliate the plants significantly, therefore, reducing
the plant's ability to photosynthesize and further reducing the plant's nutrients required
for healthy growth and reproduction.
Predicted and native habitat
Aphthona lacertosa have shown a preference for open or lightly shaded sites with
clay loam soils, establishing on heavier soils than A. nigriscutis and A. cyparissiae.
They have a wide adaptation to climatic conditions, accepting mesic-dry to moist areas, avoiding
very dry sites. Similarly to A. czwalinae, they too prefer sites with well-developed
mixed vegetation surrounding shorter host plants. They are capable of filling a niche in areas
the other species do not. A climate with a 4-month period of temperatures of 10°C or
less is required for complete development. Like all Aphthona species, they too compete
poorly where ant populations are present.
British Columbia Experiences
Origin:
The origin of A. lacertosa populations released in BC came from North
Dakota, USA, reared from Hungarian stock. They arrived in a mixed
population with up to 80% A. czwalinae.
History:
A. lacertosa was first introduced to BC in 1995 in a mixed population with A.
czwalinae.
They were released at two locations, one in the north Okanagan and the other in the south Cariboo.
Only a few releases were made from imported populations between 1995 and
1997. In 2000, the first small field collection was made from what has
become the only collection site in BC.
Habitat:
Limited releases have been made into the Bunchgrass, Interior Douglas-fir and Ponderosa
pine biogeoclimatic zones. They have established in the Interior
Douglas-fir and Ponderosa pine zones. It is believed that the plants at the site
in the Bunchgrass zone occur at a density that is less desired by the
flea-beetles.
Field results:
The narrow adult emergence window requires frequent site visits to avoid
missing the agents' peak period. In the southern interior this stage
appears to last only one month. In 2000 the first field collection was made from a
site in the north Okanagan. Since this time, small collections have
continued from here and are used to supplement a previous release site and to establish a
new site near Kamloops. The earliest adult sighting have been in late May at the Okanagan site. Despite the possibility that early emerging adults have high mortality rates, a recent collection
and treatment made in May 2005 resulted in survival over its first year.
No efforts have been taken to determine which species is dominant at any of the
established locations.
Not available for general distribution at this time.
Notes
There can be high mortality in the larvae stage caused by the parasitic protozoan Nosema spp.
All Aphthona species have narrow habitat requirements and will not attack spurge growing
in unsuitable microhabitats.
It may be desirable to combine the efforts of A. nigriscutis and A. lacertosa over
rolling sites which may have pockets of habitat requirements for both.
References
Gassman, A. 1990. Aphthona lacertosa (Rosh.) (Coleoptera: Chrysomelidae): a candidate
for the biological control of leafy spurge and cypress spurge in North America. CABI. Final
Report.
Harris, P. 1994. Biological control of leafy spurge on the Prairies. Leafy Spurge News.
Vol. XVI. Issue 3.
Harris, P. 1994. Biological control of leafy spurge on the Prairies. Leafy Spurge News,
Vol XVI: Issue 3. pp. 2
Harris, P. 2007. Classical biological control of weeds established biocontrol agent Aphthona
lacertosa (Rosh.). Root beetle. Agriculture and Agri-Food Canada. January 22, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/aaphtlac_e.htm
Manitoba Agriculture, Crop Management Section. 1993. Biocontrol insect profile. Biofacts.
Provincial Government of Manitoba.
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.
Rees, N. E., Quimbly, Jr., P. C., G. L. Piper, E. M. Coombs, C. E. Turner, N. R. Spencer,
L. V. Knutson (editors). 1996. Biological control of weeds in the west.
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