Crocidolomia is a genus of moths of the family Crambidae.Common Name:
English: Croci, Cabbagehead Caterpillar (CHC), Larger Cabbage WebwormSpanish: Croci, Gusano de la Cabeza del Repollo (GCR), Gusano Tejedor Grande del Repollo
Scientific Name:
Crocidolomia binotalis [Zeller] (Lepidoptera: Pyralidae)
Geographic Distribution:
Highland tropics of the Old World. Principally: Australia
(Queensland), India, Indonesia, Taiwan, Thailand, Malagasy Republic,
Mauritius, Philippines, South Africa. Croci has only been found in
tropical and subtropical regions.
Recognition and Diagnosis:Caterpillar
Size: From 18 to 25 mm long when fully grown.
Color:Croci have dark heads and appear grey at hatching and
light green thereafter, depending largely on the color of the leaves
they are consuming. They are easily recognized by their distinctive
yellowish white stripes: three dorsal and two lateral. These stripes
disappear only when larvae are close to pupation.
Location: Neonate larvae are gregarious on the underside of
leaves and initially create a small window-like appearance by feeding
without completely penetrating the leaf. As third instars, ~1 cm long,
4-5 days after hatching, they move towards the apical meristem of the
plant or head. A ravaged plant center with mats of frass and silk or
false cabbage head with no real head or several small heads are evidence
of Croci damage.
Behavior: For the first 4 or 5 days from hatching, the small
larvae feed on the
underside of the leaf without eating through the uppermost leaf layer,
creating window-like damage in the leaves. After this they move to the
growing
point of the plant center or bore to the center of the head. In the
open
center, groups of Croci will conceal themselves beneath silk webbing
and frass.
Pupa and Cocoon
Size: 8.5 to 10.5 mm long and cylindrical in form.
Color: Croci pupae are olive green and light brown turning
darker coppery brown closer to eclosion. Larvae weave a loose cocoon
which they cover with bits of available substrate, usually soil.
Location: Larvae burrow into the soil near the base of the host plant to pupate.
Adult Moth
Size: Male Croci are usually slightly larger and longer
than females. The male wing span is 20-25 mm and body length 11-14 mm.
Female wing span is 18-25 mm and length 8-11 mm.
Color: In both males and females there is considerable
variation in delineation of beige markings on the cream background of
the forewings. Males, in general, display great delineation and can be
recognized by a dark tuft of hairs on the anterior margin of each
forewing which the females lack.
Location: During the day they rest in the shade and can be stirred by hedgerow and crop plant canopies.
Behavior: Croci are active in the twilight, night, and dawn
hours. Adult females can live as long as 30 days and lay as many as 10
or more egg clusters for an average total of 350 eggs.
Eggs
Size:
Eggs are laid in overlapping or "shingled" masses of ~10-300 eggs. A large egg mass will measure 5 mm in diameter.
Color: Egg masses are light green in color and are easily camouflaged on host plant leaves.
Location: Egg masses are usually laid on the underside near the base of leaves.
Host:
Croci larvae feed on wild and cultivated crucifer plants. While
they are capable of surviving on any part of these plants, they
demonstrate attraction to particular plant parts such as growing
centers, blossoms and pods.
Biology and Ecology:
Croci life cycle is completed in approximately 28 days,
depending on temperature and humidity. They are almost exclusively
found in hot humid highland tropics, and constitute a more serious pest
problem during the dry season since heavy rains can drown small larvae.
Egg incubation takes 4 days. Larvae reach third instar in 4 to 5 days
at which time they begin boring into cabbage centers or movement towards
the plant parts of their choice. The remainder of their larval
development takes approximately 12 more days, during which time they
feed ravenously. Adult females can live as long as 30 days and lay as
many as 10 or more egg clusters for an average total of 350 eggs. On
cabbage crops oviposition peaks occur 35-40 after transplanting and
again 30 days later.
Damage and Importance:
Until the advent of synthetic insecticides Croci was considered
the foremost pest of crucifers in the Old World. Even a single larva
will destroy an entire plant by feeding on its growing center. Larvae
are extremely mobile and can easily travel 2 or more meters to reach a
preferred host plant. Also, as soon as larvae have begun boring into a
cabbage head they are protected from contact with insecticides. In the
Old World, Croci is a devastating pest of cabbage, particularly where
efforts are made to reduce dependence on bi-weekly pesticide
applications.
ControlManagement Strategies:
Sampling and economic thresholds:
For approximately the first 70 days from cabbage planting (or 40 days
from
transplant) monitoring for Croci damage is quick, effective, and
essential
for determining appropriate pest management action. After this time,
when the cabbage plant is larger and structurally complex it becomes too
difficult to detect Croci and sampling becomes much less effective.
Where to sample:During the first 40 days from
transplant, Croci can be effectively monitored by looking for the
window-like leaf damage created by the early larval instars. This must
be carried out twice weekly in order to detect the larvae before they
move towards the growing center of the plant.
Economic threshold: During the first 40 days after
transplant, Croci can be monitored and groups of young larvae can be
killed by hand or spot-sprayed with products based on Bacillus thuringiensis
(Bt). This method is time efficient while Croci densities remain below
15%. If the percentage of plants infested with Croci exceeds 15% it
becomes more efficient to spray the entire field.
After the first 40 days from transplant, monitoring is no longer
sufficiently effective. Cabbage must be sprayed routinely twice each week.
Biological Control:
Several Hymenopteran larval parasitoids have been identified for Croci,
but none has demonstrated greater than a 7% parasitization rate. The
first egg parasitoids were discovered in 1995, but these two species of
Trichogramma have not yet been identified.
Current IPM Practices:
Planting seasonIt is preferable to plant cabbage during the rainy season when Croci populations are reduced.Hand removal of egg masses and early instarsSuccess in locating egg masses and larval groups entirely depends on
plant architecture. During the first 40 days after cabbage transplant,
while leaves are still open and relatively few, the window-like patches
created by the gregarious early Croci instars are easily detected and
squashed. During this time it takes one person less than 3 hours per
2000 plants to monitor and remove larval groups by hand. This can be
done twice each week, as larvae will not have dispersed from their
aggregation within the time between monitoring. For some farmers the
time necessary to do this during the first 28 days may be more than
seems worthwhile given the usually low (~3%) Croci densities. They may
prefer to monitor against a surprisingly high infestation only once each
week.By 40 days after transplant the time required for hand monitoring
increases significantly and accuracy of detection decreases
dramatically. Even with meticulous efforts at least 20% of a cabbage
crop can be ruined by Croci.Spot spraying Twice weekly spot spraying of Bt on only those cabbage plants with
visible Croci is an effective means of control until 40 days after
transplant and until pest densities reach 15%. Backpack sprayers that
deliver a fine mist must be used since coverage with hand held spray
bottles is not adequate.After 40 days after transplant, monitoring and spot-spraying are no
longer effective since Croci become too difficult to to detect. It is
best to spray twice weekly with Bt.Trap CroppingSome trap cropping experiments have proved very successful. In India
15 rows of cabbage were successfully intercropped with Indian Mustard
(planted 12 days prior and 25 days post cabbage transplant).
Chemical strategies:
Pesticide recommendations and consideration of resistanceCroci has not demonstrated resistance to any of the insecticides
employed for its management. The focus of the problem is assuring
contact with larvae before they begin boring into the cabbagehead center
where they are inaccessible. This leads to bi-weekly spray programs.
While this strategy very effectively manages Croci, it cannot be
considered isolated from the Diamondback moth pest complex of which it
is part. Bi-weekly spray programs easily encourage evolution of
pesticide [even Bt] resistance in DBM. In addition, in many highland
areas of Asia, Diadegma semiclausem [Hymenoptera: Chalcididae], a
larval parasitoid, has proven to provide very effective control of
Diamondback moth. Spraying against Croci decimates the D. semiclausem population.Spray techniquesUse of spreader stickers is recommended to increase spray coverage
on the waxy surface of cabbage leaves. Croci early instars will be found
on the underside of leaves so it is important to spray the underside of
leaf surfaces thoroughly. Hydraulic nozzles and those producing fine
spray mist provide the best coverage
সার্চ করুন
উত্তর সমূহ
Crocidolomia is a genus of moths of the family Crambidae.Common Name: English: Croci, Cabbagehead Caterpillar (CHC), Larger Cabbage WebwormSpanish: Croci, Gusano de la Cabeza del Repollo (GCR), Gusano Tejedor Grande del Repollo Scientific Name: Crocidolomia binotalis [Zeller] (Lepidoptera: Pyralidae) Geographic Distribution: Highland tropics of the Old World. Principally: Australia (Queensland), India, Indonesia, Taiwan, Thailand, Malagasy Republic, Mauritius, Philippines, South Africa. Croci has only been found in tropical and subtropical regions.
Recognition and Diagnosis:Caterpillar
- Size: From 18 to 25 mm long when fully grown.
- Color:Croci have dark heads and appear grey at hatching and
light green thereafter, depending largely on the color of the leaves
they are consuming. They are easily recognized by their distinctive
yellowish white stripes: three dorsal and two lateral. These stripes
disappear only when larvae are close to pupation.
- Location: Neonate larvae are gregarious on the underside of
leaves and initially create a small window-like appearance by feeding
without completely penetrating the leaf. As third instars, ~1 cm long,
4-5 days after hatching, they move towards the apical meristem of the
plant or head. A ravaged plant center with mats of frass and silk or
false cabbage head with no real head or several small heads are evidence
of Croci damage.
- Behavior: For the first 4 or 5 days from hatching, the small
larvae feed on the
underside of the leaf without eating through the uppermost leaf layer,
creating window-like damage in the leaves. After this they move to the
growing
point of the plant center or bore to the center of the head. In the
open
center, groups of Croci will conceal themselves beneath silk webbing
and frass.
Pupa and Cocoon- Size:
Eggs are laid in overlapping or "shingled" masses of ~10-300 eggs. A large egg mass will measure 5 mm in diameter.
- Color: Egg masses are light green in color and are easily camouflaged on host plant leaves.
- Location: Egg masses are usually laid on the underside near the base of leaves.
Host: Croci larvae feed on wild and cultivated crucifer plants. While they are capable of surviving on any part of these plants, they demonstrate attraction to particular plant parts such as growing centers, blossoms and pods. Biology and Ecology: Croci life cycle is completed in approximately 28 days, depending on temperature and humidity. They are almost exclusively found in hot humid highland tropics, and constitute a more serious pest problem during the dry season since heavy rains can drown small larvae. Egg incubation takes 4 days. Larvae reach third instar in 4 to 5 days at which time they begin boring into cabbage centers or movement towards the plant parts of their choice. The remainder of their larval development takes approximately 12 more days, during which time they feed ravenously. Adult females can live as long as 30 days and lay as many as 10 or more egg clusters for an average total of 350 eggs. On cabbage crops oviposition peaks occur 35-40 after transplanting and again 30 days later.