Island pinhole borer a nightmare for invasive ‘manja konna’ trees in Kerala
THIRUVANANTHAPURAM: Senna spectabilis, or the ‘manja konna’, an invasive tree species that invaded the forests of Kerala, especially Wayanad, and nearly eradicated the flora over the years, has finally met its match.
The species is under massive attack from the ‘Island pinhole borer’ (Xyleborous perforans), an insect that has turned nature’s ally. It bores holes into the trunk of the Senna trees and lives inside, ultimately leading to their destruction.
Now, the Kerala Forest Research Institute has started monitoring and studying the insect. It was first seen by forest watchers near the jungle in Kakkapadam in Wayanad. “The watchers noticed some Senna trees had dried up. While inspecting the trees, they spotted the insects and reported it to us. We informed the KFRI for further investigation,” Wayanad Assistant Conservator of Forest Sooraj told TNIE. He said they had been trying to end the Senna invasion through methods such as debarking, cutting and uprooting the trees.
The island pinhole borer is just above 2mm long. It infects the Senna trees in large numbers by boring holes into their trunks. “The insects live within the tree,” KFRI chief scientist T V Sajeev said.
“In the investigation, we found that the female of the species carry fungal spores and start cultivation of the fungus once they settle inside the tree trunks. Both the larvae and adults of insect species feed the fungus and it ultimately results in the destruction of the Senna tree,” Sajeev said.
A massive infestation of the insect was initially detected at Thakarappadi and Muthanga forest ranges in Wayanad and is seen spreading to more areas. Sajeev said the insect completes its life cycle in 16-18 days and constructs new galleries in the same tree or moves to another. It was identified using molecular tools by Arathy M S, a postgraduate student of St Joseph’s College, Irinjalakuda.
Since 2017, Senna spectabilis has invaded the forests of Wayanad, and it is estimated that the trees have inhabited 1,23.86 sq km of forest land in Wayanad. Now, researchers led by Sajeev, who also coordinates the Nodal Centre for Biological Invasion at KFRI, have started monitoring the insect for six months. “We have to make sure the insect survives the monsoon season too. Now in areas where the Senna has been destroyed, animals like deer, buffalo and elephants are being spotted. Grass is also growing there,” Sooraj said.