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Control method developed against invasive alien insect

Barnacle wax scale insect causes severe damage fruit-bearing plants

N.S. Swathy, a postgraduate student of Sree Kerala Varma College, Thrissur, has developed an early detection and rapid response (EDRR) method against an invasive alien insect, which causes severe damage to host plants, especially fruit-bearing plants.

Barnacle wax scale insect (Ceroplastes cirripediformis) destroys the host by sucking its fluid and excreting honeydew to cause coal smudge. The insect was identified as invasive scale by the Centre for Agriculture and Bioscience International in 2017, as it causes severe damage to host plants, causing significant economic loss.

Native to the southern United States and the Caribbean islands, the insect later spread to Bulgaria and China. In 2020, Chinese researchers had predicted its spread to more regions, including India, owing to climate change.

Wilting passion fruit wines was reported by George Mathew, a researcher, to the tree health helpline of the Kerala Forest Research Institute (KFRI), Peechi, in late 2020.

Being a new incidence, the problem was assigned to Ms. Swathy as part of her student project. In her study, she found the first and second nymphal instars (developmental stages) infest the leaves of host plants and migrate into the woody tissues during the third instar. The eggs are protected by the adult female before hatching.

She conducted molecular bar coding using the CO1 mitochondrial gene to fix the identity of the insect. The bar code sequence has been deposited at the GenBank of the National Centre for Biotechnology Information.

The methods of control perfected by Swathy were successful in diffusing two populations of the insect — at Parli and Dhoni in Palakkad district.

“The insect feeds on host plants from 119 genera in 63 families and has now been reported in more than 32 countries. Being highly polyphagus, it feeds on citrus, guava, passion fruit, hibiscus, rambutan, ixora, champaka, passiflora, nerium, ficus, cycas, and mango and Jackfruit trees,” said Dr. T.V. Sajeev, Senior Principal Scientist, KFRI, who coordinates the Nodal Centre for Biological Invasions (NCBI) at the institute.

Unlike in its native range, in all the invaded locations the insect has caused serious impact on its host plants owing to the absence of natural enemies in their new countries of arrival, Dr. Sajeev noted.

EDRR is considered to be the best method in managing invasive alien species, since it is cost-effective. Once spread to larger areas, detection and management will be difficult.

“The insects are hemispherical in shape with 3 to 5 mm in length. Body colour varies from reddish brown to brown and covered with wax, appears to be pearly white. Several black and brown spots are present around the shell. Owing to the cryptic nature, they are difficult to control. The growing females draw large amounts of sap from twigs, minimising leaf growth,” said Ms. Swathy.

The NCBI at KFRI where she did her work is taking steps to alert line departments so as to detect satellite populations of the insect in other areas.

“This is the first case of the demonstration of successful EDRR in Kerala. The management of many invasive species like the Giant African Snail, Senna spectabilis tree, plants like Lantana camera and Mimosa diplotricha, the strangling wine Mikania micrantha have all established large reproducing populations, making it extremely difficult to control. We expect that the barnacle scale can be successfully eradicated through EDRR. In the case of the Barnacle wax scale, quick results from Swathy’s work helped us mount surveillance and immediate response,” Dr. Sajeev pointed out.

Any cases of new species sightings can be reported to the NCBI at 0487-2690390 for immediate identification and response.

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