Importance of biological control in Indian agriculture
- Part 2 -

SM Haldhar, EVD Sastry, M Premjit Singh *

BIOLOGICAL CONTROL OF WATER HYACINTH, EITHHORNIA CRASSIPES (MARTIUS)

Water hyacinth, Eichhorniacrassipes, a free-floating aquatic weed of South American origin, ranks among the top ten weeds worldwide. It is one of the most noxious weeds known to man and has spread to at least 50 countries around the globe. First introduced into Bengal around 1896 as an ornamental plant, it has spread throughout India and occupies over 200,000 ha of water surface. Water hyacinth is considered to be the most damaging aquatic weed in India.

Three exotic natural enemies were introduced in India viz., hydrophilic weevils, Neochetinabruchi and N. eichhorniae and galumnid mite Orthogalumnaterebrantis from their original home via USA in 1982 for the biological suppression of water hyacinth. N. eichhorniae and N. bruchi are slow in managing water hyacinth in certain areas. The impact is more pronounced in partially shaded areas or under bridges.

BIOLOGICAL CONTROL OF COTTONY CUSHION SCALE, ICERYA PURCHASI MASKELL

Iceryapurchasi (Origin: Australia) was probably introduced on imported orchard stock or flowering plants from Sri Lanka and it spread to cultivated wattles, rose-bushes, and citrus. It was first reported from Nilgiris (Tamil Nadu) in 1928 as a pest of cultivated wattle, Acacia decurrens and another Acacia spp.

The coccinellid beetle, Rodolia cardinalis (Origin: Australia), which has an excellent track record for the suppression of cottony cushion scale, I. purchase was introduced to India In 1926 via USA (California) and South Africa and in 1930 via Egypt for the control of I. purchase. The beetle was released in the Nilgiris in 1930 and it successfully controlled I. purchasi.

BIOLOGICAL CONTROL OF COMMON MEALYBUG, PLANOCOCCUS CITRI (RISSO)

Planococcus Citri was identified from citrus in southern France. From its original home, it has spread to many countries of the world. In India, it is a pest of citrus, coffee, passion fruit, cut flowers, and many other fruit crops and wild plants. Continuous drought causes an outbreak of this pest.

The damage caused by mealybug is similar to that caused by other soft scale insects, but this pest prefers to feed on the fruit stalk or the berries resulting in their drop. The encyrted parasitoids Leptomastix Dactylopii (Origin: Brazil) was introduced into India in 1983 from Trinidad, West Indies.

It is capable of parasitizing Planococcus Citri and P. lilacinus. It was produced on ripe pumpkins infested with 15-20 day old P. citri by exposure to 1-2 day old L. dactylopii females in the host-parasitoid ratio of 40:1. In lime and lemon orchards, L. dactylopii was found to be highly compatible with indigenousparasitoidCoccidoxenoidesperegrinus preferentially attacking the later instars and leaving the early instars for C. peregrinus.

BIOLOGICAL CONTROL OF SPIRALING WHITEFLY, ALEURODICUS DISPERSUS RUSSELL

Spiralling whitefly, Aleurodicus dispersus, a native of Caribbean region and Central America was introduced into India in 1995. First reported from Kerala, it has spread to all the southern states causing serious damage to several plants. It attacks over 253 plant species belonging to 176 genera and 60 families. It causes serious damage to avocado, banana, cassava, guava, papaya, and mango, besides several ornamental and avenue trees.

Exotic aphelinid parasitoids, Encarsiaguadeloupae and E. sp. Nr. Meritoria (Origin: Caribbean region/Central America) collected from Minicoy Island of Lakshadweep and brought to main land have established well, causing perceptible reduction in pest population. Parasitism levels due to both parasitoids vary from 29-70% and exceed 90% during some parts of the year.

BIOLOGICAL CONTROL OF CARROT WEED, PARTHENIUM HYSTEROPHORUS LINNEAUS

Parthenium hysterophorus, also known as the white top and congress grass, is native to the area around the Gulf of Mexico including the West Indies, and central South America. It has accidentally been introduced, over the past five decades, into many countries including Australia, China, India, Israel, Madagascar, Mozambique, Nepal, South America, and Vietnam. In India, it was recorded from Pune in 1955.

It has spread all over India covering most of the vacant and marginal lands. P. hysterophorus is known to suppress local vegetation by the release of growth inhibitors through leaching, exudation of roots, the decay of residues, etc. In 1983, a chrysomelid beetle Zygogramma Bicolorata was imported from Mexico for the management of parthenium. Adults and larvae of Z bicolorata feed on Parthenium leaves.

The early-stage larvae feed on the terminal and axillary buds and move on to the leaf blades as they grow. It performs better in well-distributed heavy rainfall areas. When Z. bicolorata numbers are very large, related plants such as Xanthium occidentale (=X. strumarium) and Lagascea Mollis are also attacked, but these are both weeds and the damage caused does not cause any problem.

BIOLOGICAL CONTROL OF SIAM WEED, CHROMOLAENA ODORATA (LINNAEUS) R. KING & H. ROBINSON

Chromolaena Odorata, a native of West Indies and continental America, is a serious weed of pastures, forests, orchards and commercial plantations in the south and north-east India. It migrated to Assam during the First World War where it is locally known as Assam-lata or Assam-lota. It is also known as German bane, because of its introduction during the German war.

After it spread to the entire north-eastern region, in 1924-25 it further spread to West Bengal. In September 1984, about 70 field collected larvae of P. pseudoinsulata were obtained by the Project Coordinator, All India Coordinated Research Project on Biological Control through the CIBC Indian station, from Sri Lanka.

P. pseudoinsulata has established here, disperses from this focal point to the surrounding areas during the rainy season and causes extensive defoliation if the rainfall is well distributed. P. pseudoinsulata can effectively suppress the weed in areas that receive well-distributed rainfall almost round the year, so that leaves of the weed are available to it for feeding.

CONCLUSION

Agricultural production is best with several new challenges, making further growth possible only if these challenges are met appropriately and timely. Crop production with modern farming techniques is reaching a plateau in most of the countries including India. Also, these modern agricultural production practices have led to environmental problems. Among these the excessive use of pesticides is the main problem.

So, biological control can be an alternative, which may play an important role in achieving the goal of agriculture. Overall, the classical biological control offers highly effective and environmentally friendly solutions to the problem of invading alien weeds. A strong national and regional policy is required to accelerate the effective implementation of biological control programmes.

Some pest species are widely distributed in different continents, but their natural enemies are effective in one area and absent in others, hence suitable species could be considered for study and introduction from one area to another.

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