Studies on phytophagous whitegrubs of Himachal Pradesh

Abstract

The scarabaeid beetles were collected on UV light traps and directly from host trees in Himachal Pradesh during 2011 and 2012. The light trap studies were conducted at Palampur, Kullu, Dallash, Shillaroo, Kheradhar, Kwagdhar, Bharmour and Reckong Peo. A total of 55 species were collected on light trap and five most common species were Brahmina coriacea, Adoretus lasiopygus, Anomala lineatopennis, Maladera insanabilis and Holotrichia longipennis. They comprised 9.88-10.05, 7.18-7.76, 7.13-7.27, 6.80-7.62 and 5.22-5.30 per cent during 2011-12, respectively. The value of Shannon index (H') was found to be maximum (H'=3.01-3.03) at Palampur and the value of Pielou’s evenness index (J') ranged from 0.89-0.90. These values indicate maximum evenness and abundance of species at Palampur. The Shillaroo area had the lowest Shannon index (H'=1.12-1.17) and Pielou’s evenness index (J'=0.46-0.49). This showed least species diversity and higher unevenness of scarabaeid beetles at Shillaroo which is due to the sole dominance of B. coriacea. On host trees, altogether 78 species were collected from 11 districts of Himachal Pradesh. On the basis of size of population, five dominant species in Himachal Pradesh were B. coriacea (48.4%), H. longipennis (9.70%), Autoserica phthisica (5.19%), M. insanabilis (4.95%) and Schizonycha sp. 1 (3.88%) on different host trees. The Shannon index (H') was calculated to be maximum at Nauni (H'=2.48) during 2011 and at Dallash (H'=2.49) during 2012. The Pielou’s evenness index was maximum at Dallash (J'=0.88). The value of Shannon index (H'=0.15-0.17) and Pielou’s evenness index (J'=0.06-0.07) was calculated to be minimum at Shillaroo. Thus maximum abundance of species was recorded at Dallash, whereas least variation between the species and higher unevenness in population exists at Shillaroo. A total of 86 species were collected on light trap/host trees, and a critical analysis of light trap: host trees data revealed that B. coriacea and H. longipennis are less phototactic, whereas M. insanabilis, A. lineatopennis and A. lasiopygus are more heliotactic in nature. Data on whitegrub infestation were recorded at 20 locations in crops like potato, ginger, cole crops, peas, maize, capsicum, tomato and rajmash. Maximum tuber damage (40.8-45.6%) in potato due to B. coriacea was recorded at Shillaroo, and in ginger, rhizome infestation by grubs of H. longipennis was maximum (17.8-20.3%) at Sangrah in Sirmaur district. In rajmash, grubs of Melolontha spp. caused damage and there was 21.0-26.3 per cent plant mortality at Baragran at Kangra district during 2011 and 2012, respectively. In peas, maximum whitegrub damage (21.75-25.0%) was recorded at Janjehli in Mandi district. In Jokhari area of Solan district, there was moderate attack of Phyllognathus dionysius in capsicum (14.5-19.75%) and tomato (13.2-15.4%). In ‘off season’ cabbage at Baragran, heavy incidence of Melolontha grubs ranging from 28.0-30.7 per cent was recorded. In maize, Lepidiota stigma was found to cause damage in alternate years in riverbed areas of Beas river. There was 40.2 per cent plant motality during 2011at Kheri village of Hamirpur district. Observations on biology of 16 species of whitegrubs were recorded. B. coriacea, B. flavocericea, H. longipennis, H. sikkimensis, A. phthisica, A. dimidiata, A. lineatopennis, A. varicolor, A. polita completed their life cycle in one year. Melolontha cuprescens, M. virescens and L. stigma had a biennial life cycle, whereas Schizonycha sp. 1 completed two generations in a year. In P. dionysius, overwintering takes place in adult stage, whereas in all other species, overwintering occurred in larval stage. The rastral patterns have been given for 16 species. The male and female genitalia have been drawn for 13 and 11 species, respectively.