Whiteflies (Homoptera: Aleyrodidae)                              BACK

Species complex

1. Silver leaf /cotton whitefly: Bemisia tabaci (Gennadius)
2. Greenhouse whitefly: Trialeurodes vaporariorum (West.)

Bemisia tabaci                                                 Trialeurodes vaporariorum

Distribution: Cotton whitefly is distributed throughout the northern and western regions of the Indian sub- continent, whereas, green house whitefly is cosmopolitan.

Host range: Potato, tomato, chilli, cotton, capsicum, okra, melon, egg plant, crucifers, cucurbits, tobacco and some weeds.

 Nature of damage and symptoms:

            White flies on undersurface of leaves

·         Nymphs and adults suck the cell sap.

·         Infected plants exhibit one or combination of the symptoms like vein yellowing, inter-vein yellowing, yellow blotching of leaves, leaf yellowing, yellow mosaic of leaves, leaf curling, vein thickening, leaf cupping, plant stunting.

·         Lower the vitality of the plant.

·         They also excrete honey dew on which sooty mould grows which interferes with the photosynthesis of the plants.

·         Affected plants give a sickly black appearance.

·         B. tabaci also transmits a number of viruses including Gemini viruses (PALCV).

Identification:

                        Whitefly nymphs

• Adults are 0.8-1.2 mm long with two pairs of broadly rounded wings that are coated with white powdery wax.
• The wings of B. tabaci are held in a roof-like position (about a 45-degree angle) over their bodies when at rest and hence appear more slender, whereas in case of green house whiteflies the wings are held nearly parallel/flat over their backs
• The eggs are elongated, vary in colour from a pale yellowish green to brown, smooth elongated and attached to the leaf surface by a short pedicel. They turn black before hatching.

Nymphs on emergence look elliptical.

They are sluggish creatures, clustered together on the underside of the leaves.

The immature do not look like the adults, and do not have wings or antennae. They are oval, thin, flat and often semitransparent.

Whitefly pupae can be recognized by the long waxy filaments attached to their bodies.

Life cycle:

• The insect breeds throughout the year. Glasshouse whitefly population growth can occur between 8°C and 35°C with the optimum temperatures for development in the range 28-32°C and 62 to 92% relative humidity.

• Eggs are laid singly (150-300 eggs per female during her lifetime) on the under- side of the leaves, incubation period is 3-5 days.

                                            Figure: Life cycle of white flies

·      All nymphal stages are sedentary (except first stage, crawlers) and found on the underside of leaves.

·      Nymphs grow through four stages, the fourth one is called as “puparium” (non-feeding stationary stage).

·      Become pupae in 9-14 days, pupal period is 2-8 days.

·      Total life cycle is completed in 14-122 days.

·      There are 11- 15 generations per year.

Management of whiteflies:

• Removal of weed hosts for clean cultivation.
• Avoid excess irrigation and fertilization
• Remove and destroy heavily infested plants
• Regular monitoring by using yellow sticky traps.
• In case of seed tubers, seed treatment with Imidacloprid @ 2.5-3 ml/kg of seed provides protection for 25-30 days.
• Conservation of natural enemies viz. parasitoids like big-eyed bug (Geocoris sp.), minute pirate bug (Orius sp.), Eretmocerus massi and Encarsia sp. and predator, Chysoperla carnea.
• Need based spraying of crop with Methyl-demeton 25EC @ 1.2 ml/lit of water, Imidacloprid 17.8EC @ 2ml/10 lit of water when white fly population reaches a threshold level of 2-3 adults per plant.

                          Orius sp.                                                 Geocoris sp.                  

BACK