Insect Pests of Fruit, Plantation, Medicinal & Aromatic Crops (2+1)

4. Spiralling whitefly

4. Spiralling whitefly - Aleurodicus dispersus Russell. (Aleyrodidae : Hemiptera )

• The spiralling whitefly Aleurodicus dispersus Russell poses threat to many agricultural and horticultural crops both in the glasshouse and field conditions in India.
  
• Aleurodicus dispersus, native to Caribbean islands and Central America, is reported to occur in North America, South America, Asia, Africa, Australia and several Pacific islands. In India, it was first recorded in 1993 at Thiruvananthapuram, Kerala on tapioca.
Biology

• Eggs are laid in a typical spiral pattern from which the whitefly derives its common name. Female whitefly lays yellowish white eggs, which hatch in 7 days and 4-6 days and 5-8 days. Fecundity ranges from 51.8 to 64.06 eggs/ female. There are four nymphal instars, which are greenish, white and oval.
  
• The duration of first, second, third fourth instar lasts for 2.15-6.50, 2.7-5.00, 2.9- 5.96 days and 6.5- 8.1 days. Fourth instar nymphs are covered with heavy wax material.
  
• The total nymphal period normally lasts for 12 to 14 days and pupal period lasts for 2 to 3 days. Development from egg to adult occupies 18 to 23 days and 22.5-29.66 days. Adults are larger with dark reddish brown eyes and fore wings with characteristic dark spots. Adults live for 13 to 22 days.



Adult


Host plants

• Aleurodicus dispersus is highly polyphagous and is known to attack about 500 plants in different countries and 280 in India alone. The host plants highly preferred by A. dispersus in India are tuber crop viz., Manihot esculenta, vegetables viz., Capsicum annum, Solanum melongena, Lycopersicon esculantum, Abelmoschus esculentus, Cucurbita maxima, oil seeds viz., Arachis hypogaea and Ricinis communis, fibre crop Gossypium spp, fruit trees viz., Psidium guajava, Carica papaya, Musa spp., Punica granatum and Terminalia catappa, ornamentals viz., Rosa indica, Hibiscus spp., Acalypha indica, Poinsettia pulcherrima, Michelia champaca and shade trees viz., Ficus religiosa, Baunia purpurea, Cassia fistula, Thespesia populnea, Manihot glaziovii etc.
Damage

• Nymphs and adults congregate generally on the lower surface, but sometimes on the upper surface of leaves of the host plants, stem (cassia) and fruits (papaya) and suck the sap. premature leaf fall and yellowing of leaves in groundnut in Tamilnadu. Yellow speckling, crinkling and curling of the leaves was noted when the infestation was severe on tapioca. The injury caused by heavy infestations was usually insufficient to kill the plants. The copious white, waxy flocculant material secreted by nymphs is readily spread elsewhere by wind and creates a very unsightly nuisance. Furthermore, honeydew is produced which serves as substrate for dense growth of sooty mould, which interfere with photosynthesis.
• The sticky honeydew carried by wind on the flocculant wax adheres to windows and cars and causes considerable annoyances. Complaints were received for allergies and dermatitis.
Management

• Management of polyphagous invasive pests like spiralling whitefly becomes all the more difficult because of the multitude of host plants that grow wild in nature and support the build-up of the pests.
Cultural control

• Use of clean planting material delays the appearance of the whitefly population. Pruning the heavily infested trees and shrubs was recommended to minimise the spiralling whitefly incidence. Subsequent to the pruning the population rapidly increased with in 4-5 months on guava.
Physical control

• Light trap was more appropriate tool for monitoring. A simple method for trapping large number of A. dispersus with light traps coated with Vaseline. Fluorescent light smeared with castor oil attracted and trapped large number of adults. Maximum adults were attracted and caught in yellow color sticky trap.
Chemical control

• Application of chemicals to the lower surface of infested leaves thoroughly reduces the whitefly abundance but temporarily. Tobacco extract (4%,) was found effective in minimising the spiralling whitefly. Spraying of neem oil (2%), fish oil rosin soap (4%) and detergent soap solution (5%) reduces the whitefly population. Contact insecticides like malathion and carbaryl at 0.10% were also found effective against young nymphs. Dichlorvos 0.08% was found toxic to various stages of spiralling whitefly.
  
• Triazophos 0.08% and phosalone 0.07% were equally effective against spiraling whitefly. Application of neem oil 2% and neem seed kernal extract 3% were found to be effective in suppressing the nymphal and adult whitefly population. Troazophos at 0.03% was found to be highly effective against spiralling whitefly Chorpyriphos at 0.04% was found to effective against A.dispersus.
Biological control

• Pruning the infested plants is only a temporary measure since the reinfestation starts after some time. Though certain chemicals were recommended, there are certain difficulties in managing pest by chemical means. Synthetic insecticides do not adequately control this whitefly since the nymphs are covered with heavy waxy flocculent materials. Only the adults are susceptible to the insecticidal applications.
  
• Application of insecticides would temporarily reduce the whitefly abundance. Even if the whitefly is controlled on some plants, there is heavy migration from roadside trees to the cultivated crops. Chemical control is impracticable because of abundance of host plants including extremely large size trees and wide spread distribution. Therefore, alternate methods such as biological control could help in the suppression of A. dispersus. As A. dispersus is an exotic pest in most countries, classical biological control is considered to be the best option for a sustainable management.
  
• The aphelinid parasitoids Encarsia haitiensis and Encarsia guadeloupae have given excellent control of spiralling whitefly in several countries Malaysia, Philippines, Benin, Togo, Ghana, Nigeria Guam, Taiwan, Australia, Hawaii and some other Pacific islands.