Insect Pests of Vegetable, Ornamental and Spice Crops (2+1)

INSECT PESTS OF CRUCIFEROUS CROPS

1. Diamondback moth, Plutella xylostella (Yponomeutidae : Lepidoptera)

Distribution: Cosmopolitan

Hosts: All cruciferous crops, also reported from Solanaceous and Liliaceous plants.

Nature of damage:

• Young caterpillars scrap epidermal leaf tissue, producing typical white patches.
• Older larvae bite holes on the leaves.
• The infestation is more severe in dry season, when it causes growth retardation (under sized heads).

Identification:

• Egg: Yellowish white with greenish tinge.
• Larva: Full grown larvae are 8-12 mm long, green in colour
• Pupa: pupate in silken cocoon which is about 20 mm
• Adult: 8-10 mm, grayish brown having pale white narrow wings with inner margins yellow. 3 pale white triangular markings on hind margins of each fore wing which appears as three diamond shaped spots when at rest

Life cycle:

• Incubation period 3-8 days
• Larval period 10-30 days
• Pupal period 7-14 days
• Total life cycle 4-5 weeks.
• Adult longevity 16-18 days.
• There are 8-10 generations in a year.

Salient features:

• Lay eggs singly or in clusters of 2-40 glued to the ventral surface of the leaf.
• Each female lays 20-300 eggs
• Pest is active during winter in plains, where as in hills it is active from March-April to October- November.
• Moths hide under the remnants of plants during winter.

Management:

• Indian mustard as trap crop
• Removal and destruction of plant debris after harvest and ploughing
• Intercropping with tomato or carrot reduces the incidence.
• NSKE @ 4.0 per cent and Bt formulation (Halt/ Dipel) @ 500g/ ha are also effective against the DBM.
• Periodic releases of Trichogramma brassicae @ 100000/ha
• Larval parasitoid, Diadegma semiclausm in nature.
• Need based use of insecticides like fenvalerate (0.01%) or cypermethrin (0.0075%) or deltamethrin (0.0028%) can also be used if population persists.