Excerpted from The Vegetable and Small Fruit Gazette
April 2001
Volume 5, No. 4
Biological Control of Aphids with Aphidius ervi
Cathy Thomas, Integrated Pest Management Program
Bureau of Plant Industry, Pennsylvania Department of Agriculture
The aphid that is usually found to infest vegetable crops, especially tomatoes
(Solanaceae crops) is potato aphid (Macrosiphum euphorbia). Other species
such as green peach aphid or melon aphid are also pests, especially if tomatoes
are grown with ornamental crops.
An effective biological control for potato aphid is Aphidius ervi (Aphelinidae),
a parasitic wasp that attacks larger species of aphids. Aphidius colemani,
another aphid parasite can be used for control of green peach aphid. Aphid parasites
are host specific. In other words – identify the aphid species in your crop
in order to apply the appropriate biocontrol!
Aphidius ervi can be introduced as a preventative method when the crop
is installed, or begin introductions as soon as aphids appear. Aphidius
is very efficient at searching for isolated colonies of aphids. Crop monitoring
for pest and disease development should begin at the seedling stage and continue
weekly until the end of the crop cycle. Detect and treat hot spots on a timely
basis to prevent rapid colonization of aphids.
Life cycle of Apidius ervi
Aphidius ervi is a long (4 – 5 mm), slender, and black parasitic wasp.
When the female wasp has found a suitable host, she bends her abdomen under her
legs and injects an egg in the aphid with her ovipositor. Aphids may continue
feeding and reproducing for several days, until the egg hatches. When the egg
hatches, the Aphidius larvae starts to eat the aphid from the inside and
the larva completes its life cycle in the aphid body. Effective parasitization
is obvious when the aphid swells and hardens into a leathery, brown colored “mummy”.
The parasite completes the life cycle by emerging as an adult through a round
hole at the rear of the mummy. Mummies can usually be seen 14 – 21 days after
the first introduction is made. Development time is dependent upon the temperature
and other environmental factors. One female wasp lays about 350 eggs in a lifetime.
Most of these eggs are laid in the first five days after introduction.
Application
ß Reduce or eliminate the use of toxic or residual pesticides before introducing
Aphidius or any other natural enemy.
ß Release A. ervi on a preventative basis or introduce at higher
rates (curative) when aphids are first found.
ß When aphids are first observed, introduce A. ervi at a curative
rate for 3 introductions at a 1 week interval.
ß Monitor weekly for the brown mummifed aphids. When 80% of the aphids are
parasitized, a parasite/prey balance has been achieved and no further introductions
are needed. Augment with further introductions as required since migration from
outside may occur in warmer months.
ß When pruning leaves, check for parasitized aphids (brown mummies). If
mummies are present keep these leaves in the greenhouse until new parasites hatch.
ß Discuss release rates with your biocontrol advisor.
ß When aphid populations are heavy, the production of honeydew can interfere
with the searching ability of the parasite. Heavy aphid populations can be reduced
with soft, compatible compounds or by using ladybeetles.
ß Release wasps between leaves (or near hot spots) in the morning or evening,
not in direct sunlight.
ß Protect parasites from ants. Ants feed on honeydew and thus protect the
aphid colonies from natural enemies. Install traps for ants.
ß Activity of parasites is reduced at high temperatures (above 86F).
ß Aphidius can stored up to two days at 42 to 46 F, in the dark.
Aphidius ervi products
Aphidius is usually shipped as adults or mummies.
Kopperts – ERVIPAR, www.koppert.nl ,
734-641-3763
Biobest – Ervi – system, www.biobest.be
or www.bugsandbees.com , 303-661-9546
Syngenta – Aphiline e, Syngentabioline.com, 805-986-8265
Benefits
ß Long lasting form of aphid control
ß Can be introduced preventatively
ß Excellent searching ability
In the next issue of Bug vs. Bug, I will be discussing another parasitic wasp,
Aphelinus abdominalis. If you have comments or other issues you would like to
see addressed in this column please phone or email me.
Cathy Thomas
Integrated Pest Management Program
Bureau of Plant Industry/Rm. 100
2301 N. Cameron Street
Harrisburg, PA 17110
717/705-5857
E-mail: c-cthomas@state.pa.us