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It all began one fine winter’s day in 2014 when a researcher at the Indian Council of Agricultural Research (ICAR)-Indian Institute of Horticultural Research (IIHR), Bengaluru, found white patches on tomato leaves at an experimental field.
Bending down for a closer look, the researcher spotted small greenish larvae crawling inside the leaves. These symptoms were new to him, so he consulted the Division of Entomology and Nematology at the Institute.
To verify for themselves, Akshay Kumar Chakravarthy and his team visited the field. They found gallery-like whitish patches. Entomologist Vaddi Sridhar discovered hundreds of small yellow eggs under the tomato leaves and small pinholes in the tomatoes.
The team concluded that the pest was new to India. Soon, DNA barcoding confirmed the larvae to be Tuta absoluta — the tomato moth.
Since 1917, this South American pest has been ravaging tomato and other related crops across the world. However, more recently, reports continue to flow in from regions as diverse as Greece and Africa. Though tomato is the primary host, Tuta absoluta attacks other vegetable crops as well. If not properly managed, the leaf-miner can cause 100 per cent yield loss.
The team had to check if the pest had spread. Soon, they found that it had attacked the solanaceous crops of a nearby farmer, causing damage to tomato, potato and eggplant crops.
The farmer from Shivakote, a village in Karnataka, is popular for his innovations in agriculture. To grow tomatoes, he combines and adapts a mixture of advanced and eco-friendly technologies.
One day, late in the afternoon, he noticed white patches on the leaves. Inside, there were small green worms. He then got in touch with IIHR. As we had dreaded, it was time to officially report the invasion.
A seasoned world traveler
Over the last few centuries, the tomato, originally from South America, has spread across the world. It was brought to India by Portuguese explorers early in the 16th century.
The tomato is now under threat. And it is not just tomatoes. Potato, brinjal and other solanaceous crops — plants of the nightshade family —also attract Tuta absoluta. The pest has travelled all the way from South America, over centuries, following such crops.
India is the second-largest producer of tomato, next to China. In India, the crop thrives year-long, in open fields or poly-house, providing small and marginal farmers with a secure livelihood. So, as soon as the Tuta absoluta invasion was confirmed, alerts were sent throughout the country to check its spread.
We used CLIMEX — a software that predicts the regions potentially favorable to the pest — and sent monitoring tools around the country. Still, by 2019, the deadly pest had spread to Tamil Nadu, Andhra Pradesh, Maharashtra, Madhya Pradesh, Punjab and Himachal Pradesh — major tomato growing regions.
How to best the pest?
Initially, farmers flooded tomato fields with chemicals. But the pest continued burrowing into leaves. Tuta absoluta mines tomato leaves to eat the chlorophyll content and lives in between two epidermises. Hence, insecticides sprayed on leaves do not affect it.
The IIHR recommended using the integrated pest management approach, which synergises cultural, biological and bio-rational methods. The farmers were advised to remove and burn infested plants.
Before cultivating new crops, they were to plough the fields properly and expose the soil to sunlight. This was to prevent the pest pupae in the soil from developing further. The team also suggested removing other plants from the solanaceous family, as they play alternate host for the pest.
Making a stand
As soon as the pest was confirmed in India, the team tried to evaluate and standardise pheromone traps to monitor the pest. The traps chemically lure males, mimicking pheromones secreted by virgin females. Using these traps, we can monitor and control male pest populations.
The team installed pheromone traps of different sizes and colours at different heights to find what caught more insects. The pheromones in the trap are volatile and have to be replaced after 20 days to effectively trap adults.
Pheromone traps, specifically for Tuta absoluta, are commercially available in the market. Directed by the scientists, the farmer, who approached IIHR, installed pheromone traps as soon as tomato seedlings were transplanted.
But pheromone traps, alone, cannot manage the pest. They only trap adult males. However, they do reduce reproduction and, thus, the spread of the pest, to some extent.
The team tried different permutations and combinations of the eco-friendly pesticides; and it was the staggered spraying of these that effectively managed the pest. The method is also cost-effective.
Following instructions, the farmer sprayed the fields with spores of Metarhizium anisopliae, a fungus that infects and kills insects. Then, he sprayed Spinosad, a substance made by soil bacteria that can be used to kill insects. Finally, he used Azadirachtin, a neem-based botanical insecticide, at 10 day intervals, depending on the level of pest population in the field.
These three sprayings, followed by regular removal of trapped adults in the pheromone traps, throughout the cropping cycle, helped the farmer bring the pest population below the economic threshold level.
He is grateful for the timely advice and to the Mera Gaon, Mera Gaurav programme, a scheme thanks to which farmers can easily access scientific research. Now, he, in turn, helps other farmers manage Tuta absoluta.
Lessons learned
In a primarily vegetarian country, such as India, solanaceous crops sustain and nourish billions. Pests, such as the Tuta absoluta, can set us back by centuries in the struggle to retain food self-sufficiency.
Preventing the entry of pests from other regions is a big challenge. Many developed countries have strong quarantine measures in place. In some countries, it is mandatory to remove the tomato’s calyx before it is imported as this is where the eggs lurk.
Though India has quarantine laws, implementation is lax. Lack of trained human power plagues enforcement. Besides tightening quarantine regulations, the nation would do well to equip the quarantine department with modern tools and techniques.
However, without public education on the dangers of invasive pests, seeds and plant materials from other countries will continue to be potential threats to our crops.