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Saturday, September 7, 2013

Innovative ant-based biological pest control in cashew plantation – discovered by a Kerala Farmer.

Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. More than 12,500 out of an estimated total of 22,000 species have been classified. Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies which may occupy large territories and consist of millions of individuals.   Fire ants are a variety of stinging ants with over 285 species worldwide. They have several common names, including ginger ants, tropical fire ants and red ants.

Cashew nut is a delicious popular snack – its rich flavour is liked by many and often eaten raw, roasted, lightly salted, sugared or covered in chocolate.  It is a great accompaniment for  tea,  soft drinks and hard drinks.   It is also very commonly used in Indian cuisine.  It is put in dishes like Pongal, sweet payasam, kesari and more.  Can you imagine that they add cashew nut with brinjal and make a special dish in Andhra !  The nut can be used whole for garnishing sweets or curries, or ground into a paste that forms a base of sauces for curries  or some sweets. It is also used in powdered form in the preparation of several Indian sweets and desserts.  There is also a popular country liquor in Goa known as Fenny or Feni, which is made from the juice of cashew apple.   Cashew in also harvested in tender form before the hardening of the shell and used in Kerala cuisine including aviyal.

Endosulfan was used as pesticide, especially in Kerala but has been in news in recent past for wrong reasons.   Endosulfan became controversial agrichemical due to its acute toxicity, potential for bioaccumulation, and role as an endocrine disruptor. Because of its threats to human health and the environment, a global ban on the manufacture and use of endosulfan was negotiated under the Stockholm Convention in April 2011. The ban will take effect in mid 2012, with certain uses exempted for 5 additional years.  Many countries have already banned it.  Recently, in a World Convention at GenevaIndia in a perceived change of stance accepted that the pesticide is a health hazard and  there would be a phased out ban with an exemption for some crops.  It has been used widely in Kerala as it was much cheaper than organic options.  At a stage when 84 countries had banned Endosulfan, India resisted it claiming that there existed no solid proof of its impacting human health, but found itself isolated in the convention, with another user China also supporting a conditional ban.   More set back was to follow as the Food and Agriculture Association of the UN stated it is hazardous.  Earlier, there were protests in Kasargod region which had seen high death among the farmers who used the pesticide.

Cashew  is a tree in the family Anacardiaceae; it derives its name from the Portuguese name for the fruit of the cashew tree, caju [it is kaju in Telegu also].  The cashew-nut tree is a fast grower and an evergreen tropical tree. It grows to a height of 12 m. Blossoming takes place between November and January. Seedling trees flower in the third year after planting. The fruit ripens fully within 2 months.  The nut is attached to the lower portion of the cashew apple which is conically shaped. The cashew nut (seed) hangs at the bottom of the apple, and is c-shaped.   The cashew seed has within the outside shell the edible kernel or nut.  Cashew apples and cashew nuts are excellent sources of nutrition. The cashew apple contains five times more vitamin C than an orange and contains more calcium, iron and vitamin B1 than other fruit such as citrus, avocados and bananas.  Cashew shell oil extracted from the shells is caustic and causes burns on the skin

Cashew trees are genuinely tropical and very frost sensitive.           The trees grow in a wide spectrum of climatic regions between the 25 °N and S latitudes. The cashew tree has a well-developed root system and can tolerate drought conditions. Rain during the flowering season causes flower abortion due to anthracnose and mildew.  During harvesting, while nuts are on the ground, rain and overcast weather causes the nuts to rot or start germinating.

Like any other crop, they are also affected by insects and the worst damage to cashew crops is done by Tea mosquito bug.    Tea mosquito bug   (Helopeltis theivora) is a polyphagus insect pest affecting tea, while Helopeltis antonii, affects crops such as cashew, guava and neem.     Indiscriminate use of pesticides in tea plantations has eradicated several beneficial insect predators that fed on this bug and have led to the resurgence of other pests.  Cashew plants are badly affected by Helopeltis. The insect sucks the juice from the tender leaves and stem, resulting in drying up of shoots.   Once the shoots are affected, flower production is hindered resulting in crop loss. Very often the damage is confused with drought effect. Earlier they were controlled by endosulfan which was  aerially sprayed in the government-owned large tracts of cashew plantations for  decades.

Perhaps the ban on Endosulfan would  have caused worries to  cashew growers but for the accidental discovery by a small scale farmer – N. Vasavan.    He has discovered that red ants could replace the use of pesticide to contain the attack of tea mosquito bugs in cashew plants.  This  has prompted the Kerala Agricultural University in Kasargode to refine the ant technology for larger field application. Entomology Department of the university has begun a three-year project on the use of red ants in vegetable cultivation to do away with the use of pesticides to curb the insects, apart from continuing the experiments in the cashew sector.

N Vasavan, a small-scale farmer in the district, had brought back the ant-based biological pest control in his cashew plantation when the farm sector was heavily banking on pesticides.   Vasavan planted a new variety of cashew saplings in his small holding in 2004. After two years, red ants had formed their colonies in a few plants. When tea mosquito bugs began attacking the plants, Vasavan used a local concoction of bio-pesticide made out of neem cake and garlic. “The ants perished due to the bio-pesticide. Later, I avoided the plants where the ants had formed nestles within the leaves,’’ said the 55-year-farmer. He was surprised to see that the trees where ants had harboured were growing better than those treated with pesticide. Soon, Vasavan started grooming ant colonies in his cashew shrubs.

He also happened to read an article in a magazine by Dr K M Sreekumar, an entomologist who threw light into the use of various ants to control pests several centuries back. Vasavan apprised Sreekumar about his experiment.  With the aid from the State Planning Board in 2007, the duo began steps to prove that adoption of ant technology could control bug menace in cashew plants. For the next three years, Vasavan’s 3.16 acres of land, where cashew plants grew, was converted into a lab.  The study found that the population of tea mosquito bugs as well as the damage inflicted were significantly lower in ant-treated plants for three years. By the fifth year of planting, ant-harboured plants produced four times higher yield compared to untreated plants. In ant-harboured plants, production extended up to June whereas in untreated plants, the yield was only up to April. The number of unproductive shoots was higher in the untreated plants compared to the ant-harboured plants in 2008 and 2009. The study, presented in the Kerala Science Congress in 2010, recommended that the red ant technology was a viable option for pest management in cashew.

Thus there is evidence that grooming red ant habitats in cashew plants would help increase production.  Vasavan states that  human intervention is required at the initial stage to make ant colonies. Using a rope, cashew plants could be connected with the trees having ants’ presence. Dried fish could be used as bait. Vasavan has been honoured by the government agencies for his innovative pest management system.

Nature has its innovative ways and there are individuals like Vasavan who with their ingenuous methods are doing service to the society.

Regards – S. Sampathkumar.
2nd Aug 2011.


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