Biological Control Agent: Aphis chloris (Koch)
Invasive Plant Species Attacked: St. John's
wort
(Hypericum perforatum)
Type of Agent: Sap sucking aphid
Status
Primary
Description and Biology
Adult:
Aphis chloris typically appear similar to common aphids, lime green (olive green
in cooler climates), and measure 1 - 2 mm. Self-fertile females hatch from overwintered
eggs in June and go on to produce live young. It takes the live young six days at 25°C
or 10 - 11 days at 17 - 18°C to reach the reproductive adult stage. Multiple
live young births continue until cool temperatures in the early fall. In warm conditions,
self-fertile females continue to be produced. In northern climates the onset of cool,
short days during September initiates the production of males and egg producing females.
With these cooler temperatures the females begin to lay eggs, often doing so without mating.
Each female will produce an average of only four eggs, depositing them onto basal winter foliage.
From summer until fall, winged females will disperse in crowded conditions to develop new colonies.
Adults and nymphs congregate on stems, root collars, leaf axils, flowers and leaves.
Egg:
Eggs initially are yellow, turning shiny black over time.
Larva and pupa:
Aphids do not have a larvae stage, they develop from egg, to nymph to adult. Nymphs are
immature versions of the adult.
Overwintering stage:
Eggs laid in September and October overwinter and hatch the following season.
Location and effectiveness of attack
Adult and nymph stages feed on plant fluids, avoiding the photosensitizing toxins by feeding
on phloem sap. Stems and leaves are attacked and in high populations and can cause plants
to wither and die. Often they can be located on stem bases, near the basal leaves and
root crown. In field studies, healthy potted plants were killed in one month when attacked
by A. chloris.
Predicted and native habitat
A. chloris - preferred Canadian climate is similar to maritime, where summers are
humid and temperatures are cool, 20 - 25°C. It does not do well in hot, dry
locations where plants wither and burn from heat. Sufficient cold winter temperatures
are required for egg development. Climate variations determine the life cycle pattern.
In Europe, Aphis chloris is common in a wide geographic range.
British Columbia Experiences
Origin:
The A. chloris released in BC originated from populations collected in
Austria, Germany, Hungary and Switzerland.
History:
In 1979 A. chloris was first released into the east Kootenays.
Infrequent field releases were made between 1979 and 1997 from populations
reared in Saskatchewan and Alberta. These were released within the BC
southern interior. In 2008 the first field collection was made and
released into the Fraser Valley.
Habitat:
Releases have been made in the Bunchgrass, Coastal western hemlock, Interior cedar hemlock,
Interior Douglas-fir and Ponderosa pine biogeoclimatic zones. There is
a recorded site in the Engelmann spruce-subalpine fir zone, but this still
requires confirmation. Establishment has been found in the Bunchgrass,
Interior cedar hemlock and Interior Douglas-fir and Ponderosa pine zones.
It is still too early to determine the status of the recent release made in the
Coastal western hemlock zone.
Field results:
Establishment has been found at most the release locations at this time. In 2005 aphids were located at several locations
by late spring. The next year, at these same sites, no aphids could be located
by mid August. It is not known if the prolonged heat-wave was the reason for their absence.
In 2008 the first field collection was taken from the Southern Interior Forest Region and moved
to the Coastal Forest Region. It is still too early to determine if the recent attempt to
move the aphids from the dry interior habitat to a moist site in the Fraser Valley
was
successful.
Not available for general distribution at this time.
Notes
A. chloris is the only common aphid found on St. John's wort.
In eastern Canadian maritime habitat, 60 km dispersal was recorded in eight years. Rapid
dispersal can result in low density populations.
References
Briese, D. T. 1989. Host-specificity and virus -vector potential of Aphis chloris (Hemiptera:
Aphididae), a biological control agent for St. John's wort in Australia. Entomophaga 34 (2):
247-264.
Cranston, R. S. and M. J. Malmberg. 1980. Report on goatweed (St. Johnswort) (Hypericium
perforatum) in the East Kootenay District-1980. BC Min. Agric. and Food. 6 p.
Harris, P. 2003. Classical biological control of weeds established biocontrol agent Aphis
chloris Koch. Foliage-sucking Aphid. Agriculture and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/aaphchl_e.htm
Mason, P. G. and J. T. Huber. Biological control programmes in Canada, 1981 - 2000.
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.
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