As India battles invasion of the cereal-eating moth, fall armyworm (FAW), which is now chomping its way into northeastern states, scientists have turned their attention to another incursion-from the East.
A trunk borer, suspected to have sneaked in from India’s eastern neighbours, has been quietly gnawing away at guava and litchi trees in the northeast region that shares borders with Myanmar, China, Bhutan, Bangladesh and Nepal.
The guava and litchi-trunk borer or litchi longhorn beetle (Aristobia reticulator), is an important pest of guava and now litchi in India. It has been reported in guava trees in Meghalaya and Tripura in recent years and in litchi trees in Arunachal Pradesh, where it has caused heavy damage.
And as a first step towards genetic characterisation, that will inform further studies and pest management, researchers have decoded its mitochondrial genome.
“We have just started scratching the surface in terms of understanding the stem borer. It is a longhorn beetle and it is suspected to have come in from neighbouring countries that share international borders with northeastern region of the country,” said Ganesh Behere, Principal Scientist at ICAR Research Complex for NEH Region in Meghalaya.
“Despite its significance in the way it economically impacts these fruit trees, there is no molecular data available at all for the borer,” Ganesh Behere told Mongabay-India.
The Aristobia reticulator mitogenome. Image by Ganesh Behere.
“We are in a position to deal with FAW invasion because we know so much about it, especially in the context of genetic data. Similarly, we need to have molecular data available for the trunk borer. It will also help in the correct identification of the trunk borer because the farmers are largely unaware of its infestation,” explained Behere.
Because the beetle completes its life cycle in a year with their larvae tunnelling inside the stem for that period, the infestation goes unnoticed. “The adult emerges from the trunk for reproduction but the trees are damaged by then. This is when the infestation comes to the fore,” Behere said.
A total of 163 species of longhorn beetles are known from Indian’s northeastern region which forms part of the Indo-Myanmar mega-diversity hotspot.
According to ICAR, this pest is distributed in countries such as Nepal, India, China, and Vietnam. In India, it is mainly restricted to the north-eastern region.
From Africa to Asia, the fall armyworm’s path of destruction
The guava trunk borer can be easily confused with its longhorn relative Aristobia approximator, both having a striking black body with yellow patches, said Behere.
“DNA barcoding would help us identify the exact species,” said Behere.
DNA analysis came in handy to confirm the fast-moving FAW (even at the egg and larval stage) when it had sneaked into India last year (2018), he said.
In India, where the fall armyworm was first reported in Karnataka in 2018, damage to maize fields was initially attributed to cutworms (Spodoptera litura and Mythimna separata) and the true armyworm. The hardy moth’s presence was confirmed through assessment of morphological characters and DNA barcoding according to entomologist C.M. Kalleshwara Swamy. Swamy along with colleague Sharanabasappa first detected FAW in the state at the University of Agricultural and Horticultural Sciences’ maize research plots.
The fall armyworm, Spodoptera frugiperda, is a lepidopteran pest that feeds in large numbers on the leaves and stems of more than 80 plant species, causing major damage to economically important cultivated grasses such as maize, rice and sugarcane but also other vegetable crops and cotton.
After invading the African continent in 2016, the pest then spread to India, Sri Lanka, Vietnam and six other Asian nations in 2018.
Having infiltrated southern and western India last year (2018), the fall armyworm has now been detected in northeastern states of Mizoram, Nagaland, Tripura, Manipur and Meghalaya. It is suspected to exist in Sikkim, according to an ICAR advisory. The species is subdivided into two subpopulations called the R-strain and C-strain that differ in their distribution on different plant hosts.
Kalleshwara Swamy said the population introduced in India is performing according to the biological parameters like the population in Africa and Americas and that their studies have demonstrated genetic homogeneity between the South African and Indian fall armyworm populations and substantial similarities between these and collections from eastern Africa.
Multiple lines of evidence have established that the pest is the fall armyworm. Photo by A S Vastrad.
Genetic data to inform and manage stem borer
Drawing parallels with the FAW genetic data, Behere believes carrying out studies on genetic variation on the guava and litchi trunk borer across different northeastern states would help experts pinpoint the best monitoring and control strategy.
“Because the fall armyworm invading India is genetically similar to those in other countries, strategies like pheromone traps work. But if the stem borers exhibit variations based on location, then a particular pheromone blend that works for the borer in Arunachal may not work as efficiently for the borer in Meghalaya,” Behere explained.
Pheromones are chemicals used by insects and other animals to communicate with each other. Insects send these chemical signals to help attract mates, warn others of predators, or find food.
Using specific pheromones, traps can be used to monitor target pests in agriculture or in residential areas. By constantly monitoring for insects, it may be possible to detect an infestation before it occurs.
“Through customised strategies, we can trap invasive pests and kill them in masses. Because we share international borders with several countries, constant monitoring is essential,” said Behere, adding that northeast India being pro-organic, biological control methods are preferred.
For the FAW for example, he said, although India’s guidelines for its management are uniform across the country, farmers in the northeast would opt for biocontrol rather than chemical control methods specified in the guideline.
Allan Hruska, principal technical coordinator for fall armyworm prevention for the Food and Agriculture Organization (FAO) of the United Nations, emphasised that India has the benefit of having a robust research infrastructure, a long history of crop protection, and a vigorous private sector, especially focussing on biological control.
“Of course, the concern is first on the direct impact of FAW on food security and household livelihoods. Pesticides should not be the first line of response, especially for smallholders. They usually don’t make economic sense for smallholders. And they often kill natural enemies, which are very important in naturally controlling FAW,” Hruska told Mongabay-India.
The guava and litchi trunk borer (Aristobia reticulator). Photo by Ganesh Behere.
(This story was first published on Mongabay)