A sweet solution for sugarcane woolly aphid

credit: Indian Council of Agricultural Research

In the sugarcane fields of Maharashtra and Karnataka in India, a serious outbreak of sugarcane woolly aphid (Ceratovacuna lanigera) in 2002 resulted in up to 30 per cent losses in sugar yields. Usually restricted to the northern parts of India, Orissa and Assam, the pest spread south, becoming a major constraint to production in the region, which provides one-third of India's sugar. Although natural enemies of the woolly aphid occur in the north, where the pest is usually distributed, these beneficial populations spread more slowly than the pest and thus had little impact. However, collaborative efforts between several sugarcane institutes and The Project Directorate of Biological Control have proved effective in breeding and releasing large numbers of natural enemies to boost populations in order to control the woolly aphid naturally.

Infestation of aphid on the underside of leaves causes a characteristic white coating, which is often accompanied by the development of sooty mould from the aphids' honeydew secretions. Blackening of the leaves consequently affects photosynthesis and results in stunting. In addition, farmers become greatly concerned for their own health and are reluctant to harvest infected canes. Broader-leaved varieties tend to be more affected than narrow-leaved cultivars, but most sugarcane varieties have proved susceptible to the pest, with yield losses of up to 30 per cent in severe infestations. Neighbouring fields of maize and Napier grass can also be affected.

From chemicals to biological control

Woolly aphid can be controlled with chemical pesticides but pesticides are not widely used on sugarcane, and also Indian researchers have been concerned that pesticide use would disrupt the natural control of another major sugarcane pest, the leafhopper Pyrilla perpusilla. Despite these concerns, the Department of Agriculture decided initially to use chemical sprays and soil-applied granular insecticides. However, research for a biocontrol solution was supported by a sugar institute in Pune, Maharashtra, and the Indian Council of Agricultural Research then responded by funding four major research programmes to address the management of the pest.

credit: Indian Council of Agricultural Research

Two potential predators (Dipha aphidivora and Micromus igorotus) were identified by the Project Directorate of Biological Control and field level production units were established by entomologists from the All India Co-ordinated Research Projects. The technology has proved simple and easy to standardise. Predator nurseries are created in fields under shade nets (10m x 10m) and after 3-4 months the field technicians are able to harvest over 10,000 predators, sufficient to control the pest in about 10 hectares of land, if released regularly during the peak infestation months of June-July. D. aphidivora has proved particularly voracious and, as a moth, has been able to spread easily to neighbouring areas.

Early scouting required

For successful control, early scouting is essential and, through the use of farmer campaigns, including using posters and leaflets in local languages, farmers have been encouraged to look for infestations of the aphid and to report these to the local sugar institute to trigger release of the predators. Alternatively, if the predators are already present in neighbouring fields, farmers have been encouraged to collect these and to release them into affected areas. As a result, farmers have been convinced of the effectiveness of natural control and have stopped spraying; they have also started taking measures to conserve the natural enemies to keep the aphid populations at a low level.

Classical biological control has been used successfully for many decades but it invariably takes time to identify potential predators, to test their effectiveness and to then breed them for release into affected areas. In most cases, pests have become a problem as they have been introduced to new areas and ecosystems. However, in the case of the woolly sugarcane aphid, for some unknown reason it appears to have spread spontaneously from its endemic area to infect new regions. But, as the spread was within the same country, it was relatively easy for Indian researchers to identify potential natural enemies and to then work together to breed them in sufficient numbers for release. As a result, within three years the woolly aphid has gone from being a major pest in sugarcane to one that can be readily controlled causing less than 5-10 per cent losses.

Note: The sugarcane woolly aphid is not restricted only to India. It has also been reported in Philippines, Indonesia, Taiwan, China, Japan, Korea, and Pakistan.

Collaborating Indian institutions:
Project Directorate of Biological Control; Indian Institute of Sugarcane Research, Lucknow; Sugarcane Breeding Institute, Coimbatore; Vasantdada Sugar Institute