Dwiban Pujari

Clove Oil Efficacy on the Red Spider Mite, Oligonychus coffeae Nietner (Acari: Tetranychidae) Infesting Tea Plants

The tea red spider mite, Oligonychus coffeae Nietner (Tetranychidae), is an economically important pest of agricultural and ornamental crops and considered one of the major pests of tea plants in North-east India. In view of increasing resistance recorded in insect and mite pests against pesticides, a study was conducted to determine the acaricidal, antiovipositional, repellent and ovicidal activities of clove oil (an essential oil from the clove plant, Syzygium aromaticum L. Merr. & Perry: Myrtaceae) against tea-red-spider-mite. Mortality of O. coffeae varied with the concentrations and the duration of exposure time of the mites after application of oil. Rate of deposition of eggs by mites on treated leaf surfaces as well as the viability rate of eggs decreased significantly. In addition, certain concentrations of clove oil have been proved effective against adult mites.

Faunal Composition of Scarab Beetles and Their Hosts in Assam

Field investigations were conducted in the Instructional cum Research Farm and Horticultural Orchard of Assam Agricultural University, Jorhat, to monitor the population of foliage-feeding scarab beetles on eight different host plants during 2010–2012. The highest numbers of beetles were collected from sthal-padma (Hibiscus mutabilis) (1579 numbers) followed by agar (Aquilaria malaccensis) (1526 numbers) and guava (Psidium guajava) (1348 numbers). The lowest number was found on jute (Corchorus sp.) (370 numbers). The host plants, viz., rose (Rosa chinensis), ber (Ziziphus jujuba), Silikha (Terminalia chebula), and Soalu (Litsaea polyantha) recorded 1143, 1143, 1065, and 930 beetles, respectively. The present investigation also revealed 13 numbers of new host plants of scarab beetles, viz., devil tree (Alstonia scholaris), albizia (Albizia odoratissima), dalchini (Cinnamomum zeylanicum), cocoa (Theobroma cacao), indigo (Indigofera zollingeriana), mango (Mangifera indica), Assam lemon (Citrus lemon), green gram (Vigna radiata), jamun (Syzygium cumini), rain tree (Samanea saman), mast tree (Polyalthia longifolia), jackfruit (Artocarpus heterophyllus), and drumstick (Moringa oleifera). Through scouting 20 species of scarab beetles were recorded, of which, Sophrops iridipennis, Anomala perplexa, Anomala dussumieri, and Adoretus renardi are new records from Assam.

Field evaluation of some insecticides against white grub, Lepidiota mansueta B. (Coleoptera: Scarabaeidae), on potato (Solanum tuberosum) in Assam (India)

Field studies were conducted to evaluate the efficacy of six insecticides against white grub, Lepidiota mansueta, in potato in 2012 and 2013 at Majuli river island in Assam (India). All the insecticide treatments significantly reduced tuber damage as against untreated control. Of the insecticides tested, fipronil 5 SC @ 150 g a.i.ha−1 showed low tuber damage on weight basis (5.24 and 4.57%) and was at par with fipronil 5 SC @ 100 g a.i.ha−1 (5.91 and 5.09%), chlorpyriphos 20 EC @ 400 g a.i. ha−1 (5.55 and 6.2%) and quinalphos 25 EC @ 400 g a.i.ha−1 (6.14 and 6.72%). On number basis, fipronil 5 SC @ 150 g a.i.ha−1 showed lowest tuber damage (4.2%), followed by chlorpyriphos 20 EC @ 400 g a.i.ha−1 (5.25%) and quinalphos 25 EC @ 400 g a.i.ha−1 (5.66%). All insecticide treatments were at par in tuber yield, except emamectin benzoate 5% SG @ 12.5 g a.i.ha−1. Highest cost benefit ratio was observed in chlorpyriphos 20 EC @ 400 g a.i.ha−1 treatment (2.50 and 2.62), followed by quinalphos 25 EC @ 400 g a.i.ha−1 (2.23 and 1.85). Chlorpyriphos 20 EC @ 400 g a.i.ha−1 and quinalphos 25 EC @ 400 g a.i.ha−1 seem better alternatives than fipronil to reduce infestation of L. mansueta in potato.