Croci or Cabbagehead Caterpillar (CHC)
- English: Croci, Cabbagehead Caterpillar (CHC), Larger Cabbage Webworm
- Spanish: Croci, Gusano de la Cabeza del Repollo (GCR), Gusano Tejedor Grande del Repollo
- Crocidolomia binotalis [Zeller] (Lepidoptera: Pyralidae)
- 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.
- 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.
- 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.
- 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 season
- It is preferable to plant cabbage during the rainy season when Croci populations are reduced.
- Hand removal of egg masses and early instars
- Success 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 Cropping
- Some 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 resistance
- Croci 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 techniques
- Use 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.
- Othman, N. 1982. Biology of Crocidolomia binotalis [Zeller] (Lepidoptera: Pyralidae) and its Parasites from Cipanas Area (West Java). PhD thesis BIOTROP. SEAMEO Regional Center for Tropical Biology, Bogor, Indonesia.
- Schellhorn, N. 1995. pers. comm. from Seribu-dolok, North Sumatra.
- Schellhorn, N. 1995. Farmer Trainer's group experiment and control strategy for a cabbage pest Crocidolomia binotalis [Lepidoptera: Pyralidae], in the highlands of North Sumatra.
- Srinivasan, K. and Krishna Moorthy, P. N. 1991. Indian Mustard as a trap crop for management of major lepidopterous pests on cabbage. Tropical Pest Management 37(1), 26-32.
- Technical content
- Nancy Schellhorn, Nooraini Othman, and Rebecca Smyth
- Cathy Weeden, Alfredo Rueda, Tony Shelton, and Linda McCandless
- Rebecca Smyth
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