Know your pest : Spiralling Whitefly

Arati Ningombam / Romila Akoijam / Aruna Beemrote / Ajitkumar Ningthoujam / Ayam Gangarani / Sushmita Thokchom *

If you are an avid gardener and interested in nature, I am sure you might have noticed some white-bearded-looking patches on the leaves of plants. An alien is lurking in the garden in your surroundings. They can be seen on guava, canna, banana, and banyantree leaves growing on the roadsides.

On closer inspection, you will see white insects covered by a white waxy flocculent thread-like substance. This insect is a native of Central America, the Caribbean region and the Pacific islands. It is an invasive alien insect species in India. Climate change is considered to be one of the reasons for its range expansion.

It is named Spiralling Whitefly because it lays eggs in a spiralling pattern. This whitefly has already spread to Africa, Asia, Australia and almost all the tropical regions of the world. It was first recorded in India in 1993 at Thiruvananthapuram, Kerala on tapioca.

It is a polyphagous pest that can feed on multiple host plants and complete its lifecycle on many crops. Thus, it can persist easily in our cultivated crops, including ornamental plants. It was reported in India on more than 481 host plants belonging to 295 genera and 90 families, including several vegetables, fruits, ornamentals and avenue trees.

Spiralling whitefly, Aleurodicusdispersus Russell has been reported from other NE states from many horticultural crops, including ornamental plants. This pest was reported from Manipur on new host, King chilly, U-morokin 2018. The insect has demonstrated that it could infest new hosts in newly invaded areas and potentially threaten biodiversity like any invasive alien species.

Nature of Damage

The young ones, called nymphs and adults, suck sap from leaves and young shoots. They excrete honeydew, a sugary, watery substance and a white, waxy, fluffy material that hampers photosynthesis. This white waxy material also protects it from most insecticidal sprays and is a disadvantage for farmers.

Due to this waxy flocculent matter, pesticides cannot come in contact with the insect body and are rendered ineffective. It also affects the overall appearance of the plants.

Fungal growth on honeydew secreted by the insect follows soon after.Sooty mould develops on the honeydew secreted on the plant, causing further damage. Leaves under heavy infestation were found crinkled and dry due to sucking by the pest.

Honeydew secreted by the whitefly covers the leaves, and sooty black moulds can grow on them. Plants develop a black colour on leaves and look covered by a white cottony substance orwhite "bearded" appearance fromafar due to the fluffy wax.

Heavily infested plants become stunted, and their leaves become yellow, leading to decreased leaf yield and fruit production. The spiralling effect often occurs on the lower surfaces of leaves, but in severe infestations, it is also observed on the upper surface of leaves, fruits, and non-plant materials.

Biology of Spiralling Whitefly

The spiralling whitefly is a tiny insect that sucks plant sap and is closely related to mealybugs and aphids. Adults resemble a little moth and possess a body length of approximately 2 mm. The wings of adult individuals are white, with occasional pale or black markings seen on the forewings. Eggs are oval-shaped with a golden to brown tint.

They are accompanied by randomly spiralling layers of white, fluffy wax. The initial phase of the larva is capable of movement (crawler), while the subsequent developmental phases are stationary.

The crawlers and other nymphal stages exhibit an oval, flattened shape and are white. The immobile larvae show distinctive waxy tufts, while the mature larval stage (pupa) possesses wax rods that resemble glass on either side of the body.

Management

The best way to manage this pest is by regular monitoring and scouting to prevent its establishment in a field or garden. Once established, it is difficult to manage, as a few nymphs or adults that survive control measures can start to colonize fast if weather conditions are favourable- warm and humid.

o Horticultural mineral oils like Hortimin and Lastraw are the best and safest way to manage this pest. These mineral oils dissolve the waxy protective flocculent material surrounding the pest and render the insect vulnerable to abiotic stress while clogging the insects' breathing pores (spiracles).

They can be used @ 5ml/litre water to control whiteflies and other soft-bodied sap suckers. However, they should not be used under elevated temperatures beyond 25oC. They are non-insecticidal formulations.

o Verticillium lecanii, a microbial insecticide, is another effective organic option that reduces spiralling whitefly incidence and egg laying within seven days @ 5ml/ litre of water.

o Some ready-to-use salt-based organic mixtures for soft-bodied sap-sucking pests with a mealy/waxy coating are available in the market for kitchen, garden, or home use. They are naturally safe, non-toxic, non-insecticidal, biodegradable and outperform synthetic chemical insecticides.

It is a persistent pest with fast reproductive ability, so repeated sprays are necessary, which are much better than chemical pesticides to combat this insect.