and Agri-Food Canada Insect Identification Sheet No. 43 March
species occurs wherever cabbage is grown in North America.
It is often found on the same plants with the imported cabbageworm,
Pieris (=Artogeia) rapae (L).
The greenish larvae of the cabbage looper feed mainly on the leaves
of cabbage plants, but they are also known to attack cauliflower,
broccoli, brussels sprouts, turnip, lettuce, tomato, celery, spinach,
rape and tobacco. In heavy infestations, as many as 25-30 larvae
per cabbage head have been observed. Even in lighter infestations,
the damage caused by the feeding larvae, or caterpillars, can stunt
the growth of susceptible crops.
The adult moth, which flies at night, has mottled brownish fore
wings, each marked by a small silvery spot. The hind wings are
pale brown to bronzy. The female lays up to 100 round, greenish
white eggs on both surfaces of plant leaves. Eggs are laid singly
during May or early June. After hatching, the larvae feed on the
cabbage heads and when full grown, pupate in cocoons on various
parts of the plants. The adults emerge in about 2 weeks. There
may be as many as three generations each year. The insect in the
pupal stage, but most infestations arise from adult moths migrating
from the United States.
The cabbage looper is so named because the larva, with three pairs
of legs near the head and three pairs of prolegs at the rear, crawls
by doubling up to form a loop, then projecting the front end of
the body forward.
looper may be controlled by spraying or dusting with a residual
insecticide or with Bacillus thuringiensis. Plant stalks
remaining after the crop has been harvested should be destroyed
and the field plowed. It may also be helpful to remove
weeds on which the first generation of larvae can develop, e.g.,
shepherd's purse, wild mustard and peppergrass. Natural enemies
of the cabbage looper also contribute to its control. These include
a polyhedral virus and four species of parasitic insects.
Cole Crops Monitoring:
by Conrad Berube
Take 15 paces
then drop to take sample unless plants are particularly infested;
inspect leaves for leps and aphids; 5% infestation is threshold
for wooly aphid.
There are three generations per year of imported cabbage worm
and diamond-back moth. Previous work on thresholds was done by
Harcourt: .67 cabbage looper equivalents = 1 imported cabbage worm.
1 diamond-back moth = .2 cabbage looper equivalents.
The idea is
to use one model unit to simplify threshold calculations — .75
cabbage looper equivalents/ plant (for at least fifty plants)
is the threshold. Threshold for cabbage and cauliflower is .25
cabbage looper equivalents during the heading to harvest stage.
The disadvantages are that all insects on a whole plant must be
counted which requires basic identifying skills. Binomial model
is presence/absence system that uses damage on plant as basic parameter
(which has the advantages that less training is needed, less time
to scout fields, more user-friendly). 303, 40-plant samples demonstrated
that of 152 decision-events, in over 90% of cases the same decisions
were reached using a 40% infestation threshold compared to .25
cabbage looper equivalents threshold. Further testing of the threshold
criteria for both protocols revealed curves that were very similar
and yields that exhibited no significant difference in harvest
yields. There was a significant savings in labor in labor with
presence/absence protocol (14 mins for 10 plants for cabbage looper
equivalents model 8.7 minutes for binomial sampling). Diamond-back
moth and imported cabbage worm have high potential for biocontrol
through a conservation approach.
insularae is a very effective parasitoid for diamond-back
glomeratus, and Copidosoma (a polyembryonic
egg-pupal parasitoid) are part of an effective parasitoid guild
of imported cabbage worm.
Trichogramma work on cabbage looper. A tachinid (Vorea
pupates right on looper larva.