Pest Alert: Swede
Midge in New York State (October 14, 2004)
On September 20, 2004, two Swede midge (Contarinia
nasturtii) specimens from Niagara County, New
York, were trapped in experimental pheromone traps
that Cornell Cooperative Extension Service is field-trialing
in North America with the Swiss Federal Research Station
for Horticulture. These are the first detections in
the United States. Massachusetts will survey for swede
midge in 2005 as part of the USDA Cooperative Agricultural
The swede midge is native to Europe where it is a
major pest of crucifer crops. The presence of the
swede midge in North America was first confirmed in
2000 in Canada. The damage growers had seen since
1996 was mistakenly attributed to nutrient deficiency.
No one knows how the swede midge reached North America
or exactly how long it has been present in Canada.
Swede midge has been found in 12 municipalities in
Ontario and 1 in eastern Quebec.
Hosts: While swede midge will attack
any member of the brassica family, the highest levels
of damage have been seen on broccoli, Chinese broccoli
(gai lan), Brussels sprouts, cauliflower, Chinese
cabbage, and other Asian greens. Wild crucifers are
also hosts for swede midge.
Lifecycle: Multiple (3-4) overlapping
generations have been seen in the field in Canada
with major peaks occurring during late June, late-July-early
August, and late-August-early September. The swede
midge overwinters as pupae in the soil and emerges
in the spring. The adult is a small (1.5-2mm) light
brown fly with hairy wings indistinguishable from
other midges. Eggs are very small (0.3mm) and laid
on the youngest parts of the plant (e.g. flowers buds,
leaf bases) often near the growing point. Eggs are
transparent when first laid and change to a creamy
white color as they mature. The larvae feed in groups
in protected areas of the plant tissue typically near
the growing point for 10-12 days before dropping to
the soil to pupate. Full-grown larvae are 3-4 mm long
and yellowish in color. Adults can emerge from the
soil for the next generation in two weeks depending
on climatic conditions.
Damage symptoms: Damage symptoms
are caused by larval feeding. Larvae secrete substances
to break down the cell during feeding causing changes
in the physiology of the plant. The following damage
can be caused by the swede midge: brown corky scarring
especially along petioles, distorted and twisted leaf
stalks, death of the growing point resulting in a
blind head, crinkled and crumpled heart leaves, deformed
and asymmetrical heads, and multi-headed or multi-stemmed
plants resulting from destruction of growing tip.
Swede midge damage can look like other common physiological,
nutritional, and insect problems found in cole crops.
One needs to find larvae within the plant to confirm
swede midge is the cause of the damage. Examine suspect
plant tissue with a hand lens or place the affected
plant part in a black plastic bag in the sun for several
hours to force the larvae to leave the plant tissue.
Swede midge damage is most often found in areas sheltered
from the wind such as field edges and buildings because
the swede midge is a poor flier and prefers areas
of low wind movement.
The pest alert is from the Massachusetts Introduced
Pests Outreach Project, a collaborative project between
the Massachusetts Department of Agricultural Resources
and the UMass Extension Agriculture and Landscape
Program aimed at preventing the establishment of new
pathogens and pests in Massachusetts. Visit the project
for more information on Swede
midge and other emerging pests or to subscribe
and unsubscribe for pest alerts.