Biological Control Agent: Aphthona czwalinae (Weise).
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:
The black flea beetles measure 2.8 to 3.5 mm long. Their bodies are tapered at the
front. Typically their rear upper legs are black (but can vary to brown), appearing similar
to A. lacertosa and , therefore, difficult to identify. As with all flea beetles,
they are capable of jumping great distances and do so readily. Adults usually appear
in June and July, but, can vary yearly depending on climate. It is known to appear 10
days later than A. lacertosa. The adults tend to congregate for feeding,
mating and egg-laying. Females begin to lay eggs one week after emergence. The
eggs are laid in clusters of 20 - 30 underground next to a spurge stem. The females seek
holes and crevices near plants to deposit their eggs, preferring to keep their ovipositior
from contacting the soil. They continue to oviposit every three to five days and produce
an average of 250 eggs over the season. The earliest emerging adults may have a high
mortality rate. Of all the Aphthona species, Aphthona czwalinae has the shortest
adult life span, usually about 2 - 3 weeks long. Females die shortly after the egg laying
period.
Egg:
The pale yellow eggs measure 0.7 x 0.4 mm and darken to brown-yellow as they mature.
The eggs hatch after 16 - 17 days when temperatures are 21°C. If the temperature
drops to 10°C the eggs do not develop until optimal temperatures resume.
Larva and pupa:
Larvae are white and slender with brown heads and often in a comma-like position.
After about 17 days incubation, the larvae emerge and move onto small roots and begin feeding.
The first instar of the larvae feed on latex-free fibrous roots. By the third instar
they feed freely on main roots, consuming all but the toughest parts. Larvae development
requires 127 degree days above 13.7°C or a minimum of 88 days at 20.5°C.
The larvae create a soil particle chamber where they will hibernate over winter for a minimum
of 4-months at 10°C or less. Larvae that do not feed sufficiently before the
onset of winter and those not exposed to the cold temperatures will not develop. Within
the chamber, pupation begins the following spring.
Overwintering stage:
Usually they overwinter in the soil as mature larvae within soil cells. Eggs may also over
winter if the temperatures are too low to hatch.
Location and effectiveness of attack
Larvae feed on root hairs, young roots and parts of the main root, reducing the plants
ability to absorb moisture and accumulate nutrients. Overall plant height is reduced to 10
- 20 cm tall. Plants will produce fewer stems and most will fail to flower and produce seed.
Adults feed on leaves, terminals, margins and shoots. Each Aphthona species
group feeds in a specific manner; black coloured flea-beetles, including A. czwalinae scrape
the leaf surfaces and occasionally perforate the leaves. Though the feeding is quite
impressive, it alone provides little impact. Dense populations can defoliate the plant significantly
and reduce the plant's ability to photosynthesize, therefore, reducing the plant's nutrients
required for healthy growth and reproduction.
Predicted and native habitat
A. czwalinae establish on prairie loam and clay soils with nearby water sources.
They do well in warm summer climates on mesic loamy sites or on well-drained, sandy or rocky
soils. They are more tolerant of shady conditions and heavier soils than A. nigriscutis and A.
cyparrissiae. They are capable of establishing at northern locations with shorter
growing seasons. In Canada, they have withstood up to three months of spring flooding,
but, will avoid continued marshy sites. They show a strong relationship to sites where Agropyron
repens and other vegetation grows taller than their host plant. Like all Aphthona species,
they too compete poorly where ant populations are present. A climate with a 4-month period
of temperatures of 10°C or less is required for complete development.
British Columbia Experiences
Origin:
The origin of A. czwalinae populations released in BC came from North Dakota, USA,
reared from Hungarian stock. They arrived in a mixed population with up to
20% A. lacertosa.
History:
A. czwalinae was first introduced to BC in 1995 in a mixed population with A. lacertosa.
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
A. czwalinae appear to maintain very low densities.
High mortality is associated with early emerged adults.
References
Gassman, A. 1984. Aphthona czwalinae (Weise), Coleoptera: Chrysomelidae): A candidate
for the biological control of leafy 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: 2.
Harris, P. 2003. Classical biological control of weeds established biocontrol agent Aphthona
czwalinae (Weise). Root beetle. Agriculture and Agri-Food Canada. October 6, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/aaphczwa_e.htm
Manitoba Agriculture, Crop Management Section. 1993. Biocontrol insect profile. Leafy spurge.
Biofacts. Gov. of Man.
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. 1996. Biological control of weeds in the west.
Zimmerman, K. editor. 1996. Leafy spurge honoree spurge biocontrol - the Canadian experience.
Leafy Spurge News, Vol. XVIII, Issue 2: 2.
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