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As is typical of species in the genus Scirtothrips, eggs are laid in the youngest tissues of plants, and feeding by adults and larvae can result in extensive cell damage to these developing tissues, leading to leaf and fruit distortion, and flower fall.
A serious pest on castor, S. dorsalis infests shoots, leaves, flowers and young fruits. The growing tips, particularly the young leaves and axillary leaf branches, are the main targets of attack. The infested plant parts turn brown to black and in extreme cases there is total deformation and defoliation. Although infestation occurs throughout the year, it peaks during drier months.
On chillies S. dorsalis causes 'leaf curl disease'. The pest occurs in such large numbers that the young leaves shrivel; heavy infestation of the tender shoots, buds and flowers causes the leaves to curl badly and the leaves are shed, fresh buds becoming brittle, subsequently dropping down. The damage is essentially due to the retardation, and in some cases to the complete cessation, of the physiological functions of the leaves (Ramakrishna Ayyar and Subbiah, 1935). Ramakrishna Ayyar (1932) recorded this species as a major pest in southern India causing the so-called 'Murda disease', or dying back, of the young seedlings. S. dorsalis causes damage to almost any soft part of the plant particularly in the shoots and leaves. Damage ranges from the slight disruption of the tissues to total deformation and disruption. The growing tip of the plant and young leaves, especially the axillary leaves, are the main points of attack. The damage is due to continuous sucking of the cell sap, leading to necrosis of the cell tissues. Eggs are also laid inside the soft tissues and the larvae leave large circular holes causing deformation of plant parts. As a result the plants may remain stunted due to the defoliation and deformation of the leaves. Leaf curl disease is called 'mudatha' (leaf curl) or 'korivi' when the plant presents a stag-headed appearance (burnt faggot).
Dev (1964) recorded S. dorsalis on tea causing damage to buds, young leaves, tender shoots and occasionally to older leaves. The injured tissues turn brown and as a result of feeding in more or less continuous lines on the buds, marks appear as sand-paper lines in the epidermis of leaves. In acute infestations, the growth of the shoot is arrested, the leaves remain small, hard and brittle, and the affected leaves become crinkled and curly, and fall from the plant.
Heavy infestation of cotton plants at the early seedling stage, in particular the cotyledons and other young leaves, results in the leaves becoming brittle and falling prematurely. S. dorsalis is also evident in mixed cropping of cotton, chillies and onion. The incidence and infestation of this species in different ecological conditions in cotton fields is also known (Ananthakrishnan, 1969, 1971, 1984).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Chillies suffer badly through heavy infestation by S. dorsalis of the tender shoot, buds and flowers. S. dorsalis is responsible for leaf curl disease of chillies. Heavy infestation causes the leaves to curl badly and the leaves to be shed, fresh buds become brittle and subsequently fall. During bad seasons, 25-55% of the total yield is lost (Ramakrishna Ayyar, 1932; Ramakrishna Ayyar and Subbiah, 1935).