Biological Control Agent: Hyles euphorbiae (L.)
Invasive Plant Species Attacked: Leafy spurge (Euphorbiae esula) and cypress spurge (E. cyparissias).
Type of agent: Foliar feeding moth
Status
Primary
Description and Biology
Adult:
The large brown hawk moths have colourful pink, white and black
markings on their wings that measure up to 8 cm across.
Their markings are distinct, but, can be easily confused with
similar native species.
A modified mouth part enables them to perceive the sound of bat
cries. The moths can be
located in the field from late May through June (depending on
location) and again in August and September and feed on the plant
nectar of funnel-shaped flowers, hovering like a hummingbird.
Adults are strong fliers.
The females begin to lay eggs in May and continue to do so
through to mid September coinciding with the spurge bloom.
Each female will oviposit 70 – 150 eggs singly or in clusters
up to 50 onto leaves and floral bracts.
Egg:
The eggs are green
and measure 1 mm in diameter. The
outer egg cover remains clear during incubation which allows for observation of
the development process within.
Larva and pupa:
The larvae have five instars that take 2 – 3 weeks to complete.
Each instar has distinctly different colouring and patterns.
The first is dark black or black-green, with 6 legs and 10 prolegs. The
first instars spin thin thread webs to keep themselves from falling to the
ground. The second instars’
colour changes to green with white spots.
At two weeks, the larvae are in the third instar and will have enlarged
to 2 – 3 gm and changed their colour to green, black and red with yellow spots. The larvae are
mature when they have enlarged to 11 cm long and changed their colour to a
darker combination of the previous, but, with a crimson stripe along its back
and an added prominent black-tipped, crimson horn. The larvae appear during June and early August and begin to feed on the
spurge foliage. They are aggressive
feeders that will actively travel when hungry and prior to pupation. Feeding slows when temperatures drop below 15oC. The mature larvae burrow into the soil or plant litter to a maximum depth
of 8 cm. Soil and loose materials
are cemented together to form a water-proof chamber.
Eggs that hatch early will complete pupation in 15 – 20 days and the
others will overwinter inside the chamber, which can tolerate temperatures to
-21oC. The young pupae
are greenish-white coloured with soft bodies, whereas mature pupae are pale
brown. Pupae will measure 4 – 5 cm
long. The larvae stage is prone to
ant predation. Active feeding larvae
accumulate toxins in their skin which deters enemies, however, this protection
does not persist during the pupae stage and results in high predation by mice
and other small rodents.
Overwintering stage:
It will overwinter as a pupae in a water-tight pupal chamber within the soil. At this stage it will be most vulnerable to predation.
Location and effectiveness of attack
The larvae feeding can cause complete defoliation of plants.
Foliar feeding uses up plant nutrient reserves and reduces
the plant vigour. This agent
alone is insufficient for spurge control, but, can be combined with
the effects of other agents.
Predicted and native habitat
Since 1992, larvae sightings have become common in southern
Alberta
and are alleged to be the result of dispersals from
Montana. In
North America,
established sites are associated with habitat that offers some tree
shelter. They require thick
growing infestations. Birds, small animals and rodents will feed on the pupae, therefore,
sites free from these or with fewer predators are better suited. Avoid sites with large ant populations. Hyles euphorbiae is established in
Ontario
on cypress spurge, which was the source plant for redistribution in
North America. Originally it was predicted they would require relatively warm
winter temperatures, however, establishment in
Montana
has shown otherwise.
Its native distribution is from south and central Europe and
into central
Asia
.
British Columbia Experiences
The first H. euphorbiae release was made in the East Kootenays in 1966, from
stock that originated from
Germany,
but, was reared on cypress spurge in
Ontario. The current level of establishment of this agent is unknown. During the spring of 2005 there was a possible adult sighting
on leafy spurge in the vicinity of the original release.
Collection for redistribution
Not available for general distribution at this time.
Notes
At 32oC, a generation completes development in six
weeks. It is possible
that most Canadian temperatures may be too cool for this agent.
Abundant populations in the USA are prone to
a viral disease.
References
Harris, P. 2003. Classical biological control of weeds.
Established biocontrol agent Hyles euphorabiae (L.).
Defoliating morth (spurge hawk moth). Agriculture and Agri-Food Canada. May 20, 2003. http://res2.agr.ca/lethbridge/weedbio/agents/ahyleup_e.htm
Kelleher, J. S. and M. A. Hulme, (editors). 1984. Biological control programmes against insects and weeds in Canada 1969-1980. Commonwealth Agricultural Bureaux.
McClay, A. S., D. E. Cole, P. Harris and C. J. Richardson. 1995. Biological control of leafy spurge in Alberta: progress and prospects. Govt. of Alberta. 63 p.
MFR staff field 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.
Zimmerman, K. 1996. Leafy spurge honoree spurge biocontrol – the Canadian experience. Leafy Spurge News. Vol. XVIII, Issue 2: 3-4.
| 
