Diamondback Moth (DBM)


Information
Common Name | Scientific Name | Geographic Distribution | Recognition and Diagnosis | Host | Biology and Ecology | Damage and Importance
Control
Sampling and Economic Thresholds | Control Strategies
Laboratory Rearing
Video Available

Information

Common Name:

English: Diamondback Moth (DBM)
Spanish: Plutella, Palomilla de Dorso Diamante (DDM), Rasquiña

Scientific Name:

Plutella xylostella (= maculipennis) (Curtis) (Lepidoptera: Plutellidae o Yponomeutidae)

Geographic Distribution:

World wide. It is important as a pest in the lowlands in the tropics and subtropics. In temperate zones, DBM cannot survive the winter. It colonizes the crucifer growing regions at the end of the growing season, or by seedlings that come from subtropical areas.

Recognition and Diagnosis:

Caterpillar

  1. Size: From 8 to 12mm long when fully grown.
  2. Color: DBM caterpillars vary in coloration from a light brown at hatching to dark green when fully grown.
  3. Location: Underside of leaves, between veins. They can burrow into the leaves when they are small, making small white tunnels. Later, the caterpillars feed on the underside of the leaves. They do not eat the veins and often leave the upper skin of the leaf intact, which leaves a window-like appearance. They also feed on the growing tips of the young plants, preventing them from developing further.
  4. Behavior: If disturbed, they wriggle away quickly and drop from the leaf on a silk thread. They climb back on the leaf on this thread once the danger has passed.

Cocoon

  1. Size: 10 to 12 mm.
  2. Color: Dark green inside of a white silk mesh.
  3. Location: Over the leaves or in litter under the plant.
  4. Behavior: The silk mesh is added to the surface of the leaf making its removal difficult.

Moth

  1. Size: 8 to 10 mm.
  2. Color: Gray or brownish coloration. It is distinguished by having three pale, triangular markings along the inner margin of the wings. When the moth has settled at rest, these join together to form three diamond shapes along the middle of the back.
  3. Location: Moths prefer to rest under the leaves and in protective plant structures.
  4. Behavior: Moths are more active and visible at dusk. They fly around plants searching for a mate or a place to deposit eggs. Male moths are attracted to the pheromone produced by females.

Eggs

  1. Size: Very small, less than 1mm.
  2. Color: Yellow.
  3. Location: Under the leaves near the center line of the leaf, or close to the leaf veins. They are laid either individually or in small groups.

Host:

DBM live on several crucifer plants. They are a frequent pest of cabbage, broccoli, cauliflower, rape, and tsunga. For control practices, it is important to remember that mustard and other crucifer weeds are alternate hosts.

Biology and Ecology:

The life cycle can be completed in one to two weeks, depending on the temperature. In the tropics, the life cycle is shorter in the lowlands than in the mountains. DBM is a serious pest in the dry season, but heavy rain washes out the larvae. Some countries recommend not planting crucifers in the dry season because this pest is so difficult to control.

Damage and Importance:

The caterpillars feed on the leaves of cabbage, rape, and tsunga. They prefer the undersides of leaves and do not eat the veins. The damaged skin tears as the leaf grows, creating holes and tears in the leaf. DBM also feed on the growing tips of young plants, preventing further development. In broccoli and cauliflower, the damage is indirect because DBM feed on the leaves and not on the commercial flower head. Sometimes large caterpillars or cocoons are hidden in the heads, and these may be rejected for export. DBM is the most serious pest of cabbage.

Control

Sampling and economic thresholds:

DBM caterpillars are detected by visual observations of the plant. Adults can be detected by the use of pheromone traps.
Where to sample: For commercial purposes, the whole plant should be examined. Pay special attention to look for small caterpillars under the leaves in the basal part of the plant. Damage or holes in the leaves are not a good predictor of the caterpillar population.
Economic threshold: In small cabbage plots (.25 ha) in Honduras, it is recommended to sample at least 60 plants and the action threshold is 1 caterpillar per plant. For broccoli and cauliflower at the vegetative stage, the plant can support 30% defoliation. At harvest time, an infestation level of 1 caterpillar per head is the action threshold.

Control Strategies:

Biological control: There are several enemies that help to control DBM. For example, in Honduras, the parasitoid wasp Diadegma insularis (Hymenoptera: Chalcididae) can control up to 40% of the caterpillars when there is a limited use of synthetic pesticides. In Asia, the parasitoid Diadegma semiclauson has been used on a semi-commercial basis for control of DBM caterpillars.


IPM practices:
Planting season
It is preferable to plant cabbage in the rainy season when the population of DBM is deterred by the rain.
Irrigation
Sprinkle irrigation may reduce the number of caterpillars in the field. If it is applied at dusk, it may limit the activity of adults.
Plot location
It is better not to have multiple planting dates in the same area because the older plots will serve as inoculum of DBM for the new plantings. If you need to have several planting dates, plant the younger crop into the direction of the prevailing winds to make it harder for the moths to fly into new plantings.
Seedlings
Seed-beds should be distant from old plantings and new plots to be planted. It is very important that cabbage seedlings are clean of DBM before transplanting to the field. On several occasions, attacks of DBM start with seedlings that are infested with DBM.
Remove unharvested plant parts
At harvest time, it is important to cut and, if possible, remove all plant materials that are not harvested. DBM can survive in plant residues and migrate to the next plot.
Trap-crop
In some areas, farmers inter-crop cabbage with other cole crops or crucifer weeds that are more attractive to the DBM than cabbage. These inter-cropped plants should be monitored with more frequency than the main crop and require control of the DBM before it can be passed to the main crop. Unattended trap crops can generate large populations of DBM. Special care is needed to manage these crops to use them as part of a control practice.
Inter-cropping
In some areas, it is recommended to plant small plots of cabbage between other crops that are not susceptible to the DBM. The idea of inter-cropping is that DBM moths will have more difficulty in finding new crops when they are camouflaged between other non-susceptible crops.

Chemical control:
Pesticide resistance problems
DBM has developed resistance to the bacterial pesticide, Bacillus thuringiensis, var. krustaki in areas where it is in heavy use, leaving farmers without a useful pesticide.
Pesticide recommendations
Because of severe pesticide resistance problems with DBM around the globe, it is very important to use pesticides as little as possible in an IPM program. You need to contact the local authorities for the specific pesticides to use in your country. It is recommended to make a pesticide screening study to find the best pesticides to use in rotation between the different pesticide families. Remember, you must use only pesticides that are legal to use for this pest and crop in your country.
Spray techniques
Cabbage plants contain large amounts of wax in the surface of the leaves. This wax makes it very difficult for pesticides to stay on the leaf surface. It is recommended to use spreader stickers to increase pesticide coverage and persistency. The majority of DBM caterpillars live under the leaf surface. For this reason, it is very important to have an excellent pesticide coverage under the leaves. Hydraulic nozzles are the best to use with backpack or tractor sprayers. The use of electrostatic sprayers improves pesticide coverage and reduces pesticide use.

References:

Andrews K. L. 1984. El manejo Integrado de Plagas invertebradas en los cultivos Agronómicos, Horticolas y frutales en la Escuela Agrícola panamericana. Zamorano Press.
Shelton A. M., A. Turner, D. Giga, P. Wilkinson, E. Zitzanza, and D. Utete (1995) Diamondback Moth. Zimbabwe Horticultural Crops Pest Management. NYSAES, Geneva NY. 2 pp.

Credits:

Technical content
Alfredo Rueda and Anthony M. Shelton
Production
Ben Shelton, Cathy Weeden, and Linda McCandless
Pictures
From the Archives of the Integrated Pest Management Program at the New York State Agricultural Experiment Station in Geneva.

Contact Form:

For more information regarding this publication, contact Alfredo Rueda (aar4@cornell.edu). You may also contact one of our collaborators in your geographic region who may have more specific technical information on the topic.

Your contributions are important to us:

In most cases, farmers and practitioners are the real innovators in pest management. If you have made an improvement or a new system to control this pest we will be happy to publish it here. Please send a description of your discovery to Alfredo Rueda (aar4@cornell.edu ).
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    This document last modified 12/4/95 at 8:39PM EST
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