Guwahati, April 17: Scientists have, for the first time in the country, found evidence of a beetle from China infesting litchi plants in Arunachal Pradesh.

A study, carried out by M.M. Kumawat and his colleagues from the College of Horticulture and Forestry, Central Agricultural University, Pasighat, said litchi trees in the Northeast were severely damaged by a longhorn beetle, Aristobia reticulator (Voet), a stem borer. A stem borer is any insect larva, or arthropod, that bores into plant stems.

The study has been published in the March edition of The Coleopterists Bulletin.

"Recently, litchi trees in the Northeast were severely damaged by a stem borer, Aristobia reticulator (Voet). This is the first report of heavy incidence of this borer in litchi trees in India, which was earlier reported from China, said Kumawat, the lead author of the article.

He said the pest might have invaded from neighbouring China and Myanmar, where it causes heavy damage to litchi plantations.

Beetles are by far the largest order of insects, with 3.5 lakh to 4 lakh species, making up about 40 per cent of all insect species described, and about 30 per cent of all animals. The 23mm to 32mm blackish beetle has a long antenna.

"Beetles were observed feeding on bark, thereby girdling stems, branches, and soft twigs, while larvae tunnelled inside the stem. Of 382 trees examined in the survey from litchi orchards, 338 (88.5 per cent) were damaged by this pest," the study said.

The survey was done in East Siang district. Dead trees and damaged branches with exit holes and feeding tunnels were observed and recorded.

Experiments for studying the life cycle of the beetle were carried out in 2013- 2014 at the College of Horticulture and Forestry, Central Agricultural University, Pasighat, Arunachal Pradesh.

Among the affected trees, 14.8 per cent trees were heavily infested with more than 10 borers per tree.

Older trees were severely affected by this pest, and sometimes more than 10 borers were recorded from a single tree. The beetles were selective in feeding and preferred only tender and succulent branches approximately a year old, while thick, hardy branches were not preferred.

Litchi is an important high-value crop in several Asian countries. It is known for its delicious fragrant pulp and quality juice. The plant was introduced from China and has been under cultivation in the country since the end of the 17th century.

India is climatically well suited for the production of this fruit and contributes significantly to the grower's economy. In India, litchi is cultivated on about 84,000 hectares, with a yield of about 5.85 lakh metric tonnes per annum. Among many factors affecting production and productivity, insect pests and post-harvest losses are a major constraint. Litchi cultivation has just started in Arunachal. Fifty plants each of cultivated litchi, guava, China rose, Hibiscus rosa, red gram, citrus, and mango were observed for infestation and data on length of bark consumed per plant, number of observed adults and larvae per tree, and percentage of trees infested were collected.

The highest number of Aristobia reticulator were found on litchi plants, followed by guava, red gram, and China rose. The greatest amount of damage caused by the adults feeding on bark was observed in litchi, followed by red gram.

The study has warned that this beetle may spread to major litchi-growing states like Bihar, Bengal and Jharkhand, if quarantine measures are not taken.