Text and pictures by PRIYAN DE SILVA

White flies (Aleyrodidae) have become a threat to coconut and other agricultural crops in Sri Lanka. They damage plants by sucking out its juices. Heavily infested plants can be seriously weakened. Leaves often turn yellow, appear dry and drop prematurely. White flies also transmit crop viruses.

Deputy Director (Research) at the Coconut Research Institute (CRI) Lunuwila, Dr. Nayanie Aratchige says that around 1,500 species of White Fly have been reported from around the world of which four species, Aleurotrachelus atratus (Palm-infesting whitefly), Paraleyrodes minei (Citrus nesting whitefly), Aleurodicus dispersus (Spiraling whitefly) and Aleurodicus cocois (Coconut whitefly) are presently a threat to coconut palms in Sri Lanka.

Dr Aratchige said that the first mention of the White Fly plaguing coconut palms was in Barbados in 1846, and that outbreaks have been reported in the Caribbean and South American regions since the 1990s and outbreaks of Rugose spiraling whitefly (Aleurodicus rugioperculatus) in India since 2016.

The species Aleurodicus dispersus (spiraling white fly) has been present in Sri Lanka since 1990 but it was previously considered a minor pest to coconut palms.

The first major white fly outbreak in coconut plantations in Sri Lanka was reported in 2019 from the Kegalle District and it is believed to have been caused by the accidental introduction of a new species via illegal importation of seedlings, the impact of climate change, sudden drop of natural enemy populations of the native population of whiteflies due to excessive use of insecticides on other crops.

Dr. Nayanie Aratchige

Dr Aratchige said that White Flies had invaded coconut plantations in Gampaha, Kegalle, Kandy, Kalutara, Colombo, Kurunegala, Ratnapura, Puttalam and even the Galle, Matara and Hambantota Districts, which have been battling the Weligama Coconut Leaf Wilt disease for over a decade.

Banana, guava, citrus, avocado, eggplant, okra, cashew, Indian almond (Kottamba), caryota palm (Kithul palm), areca nut, ornamental plants, curry leaves, green chillie, mango, jackfruit, breadfruit, neem, pigeon pea, different varieties of pepper, Water melon, coffee, etc., host the White Fly.

The Coconut Research Institute and the Coconut Cultivation Board are conducting awareness programmes on the identification of the pest and coordinated spraying of insecticides.

Sticky traps

Dr Aratchige said that placing yellow sticky traps or spraying of the following insecticides to control the menace is recommended.

Neem oil and soap mixture

(Neem oil – 10 ml, Soap powder – 05 g dissolved in 1 L of water) or

Thiamethoxam (Actara)

(3g in 10 l of water) or Carbosulfan (Marshal 20) (20ml in 10 l of water) or Chlorantraniliprole+Thiomethoxam (Virtako 40G) (2.5g in 10 l of water)

Neem oil and soap mixture is recommended for all infested areas as this mixture is less toxic to the natural enemies of whiteflies. Artificial insecticides are particularly recommended for newly infested areas and the coconut seedling nurseries.

The CRI is further researching on methods of chemical and biological control and have sought assistance from other countries for importation of exotic natural enemies of the white fly.