| Seiji Tanaka in Majuli. Telegraph picture |
Jorhat, Nov. 16: Depredation of crops on Majuli by the destructive white grub — beetle larvae that feed on roots of plants — has brought an entomologist all the way from Japan to study the species on the river island.
Seiji Tanaka, a senior researcher at the Laboratory of Insect Behaviour of the National Institute of Agrobiological Sciences at Tsukuba in Japan, visited the island yesterday and discovered that the species found here, Lepidiota mansueta Burmeister, was almost double the size of that found in Japan.
“In Japan, the larvae of the beetle species, Dasylepida Ishigakiensis, destroys sugarcane worth US $2,50,000 every year on Mayiko island, Okinawa, where it is cultivated in over 8,400 hectares. Over here, a farmer told me the larvae ate up roots of potato, sugarcane, colocasia and green gram (moong),” Tanaka said.
The Lepidiota genus of the beetle is found only in Japan and in Majuli and Jharkhand in India. The beetle, which has a two-year lifecycle, never comes overground, except for two months to mate.
AAU entomologists have been working on a national-level project on white grubs and other soil arthropods since 2004.
Principal scientist of the project, Abu Adil Lutful Haque Baruah, said L. mansueta was unique to the Northeast and affected around 23 villages on Majuli. He said it could be regarded as a rare species because the adults came out of the ground only for a limited time of the flight year for reproduction.
Senior scientist with the project Badal Bhattacharyya said on Majuli, though the pupae turned into beetles in April they remained underground, only coming out of the soil to mate. “Here, we catch them by lighting up the fields as they are attracted to light. But they come out only for half an hour and we have to catch them within that time. After mating, the females burrow deep underground and produce about 30-35 eggs in one batch.”
The researchers had caught 42,000 white grub beetles in April-May.
Gautam Handique, senior research fellow associated with the project, said though crop loss had not been assessed on the island, 42-48 per cent of potato crops, 35-40 per cent of colocasia, 15-20 per cent sugarcane and 30-35 per cent green gram had been destroyed.
During his research in Japan, Tanaka had found that by confusing the bugs’ natural rhythm through temperature variations and use of sex pheromones their proliferation could be contained. This could be done by luring out male beetles through application of sex pheromones on plants and hence, disrupting their sexual cycle.