Diversity and taxonomy of white grubs in Kasaragod district

Abstract

The research work “Diversity and taxonomy of white grubs in Kasaragod district” was carried out in the Department of Entomology, College of Agriculture, Padannakkad during the year 2023. The objectives of the research work included survey and collection of white grub adults under the family Scarabaeidae from agro-ecological units of Kasaragod district, taxonomic identification and distribution analysis, redescription and preparation of illustrated key/s of white grub adults under the family Scarabaeidae from Kasaragod district and study of male and female genitalia. Collection surveys were carried out by installing light traps, representing the five agroecological units of Kasaragod district viz., Coastal plain, midland laterites, foothills, high hills and Kaipad lands covering 11 locations viz., Manjeshwar, Vorkady, Chemmanad, Pullur-Periya, West Eleri, Balal, East Eleri, Pilicode, Nileshwar, Padanna and Kayyur-Cheemeni. The adult beetles were collected from light traps at fortnightly interval during 2023. The collected beetles were subjected to wet preservation by storing in 70 percent alcohol and dry preservation. The adults were pinned using number ‘3’ size entomological pins. The pinned specimens were labelled with the following details viz., location, date of collection, name of the collector and its geographical details. These specimens were dried at 45ºC in oven for 15 days and stored for further studies. Very small beetles were mounted onto the narrow end of a triangular white ivory card with fevicol®, later pinned and stored. In order to categorize the stored specimens into subfamilies, they were first grouped based on claws, abdominal sternal lines, antennal insertion, arrangement of metatibial spurs of the beetles. The dissection of the genitalia was done in accordance with standard procedure. Photographs and descriptive studies were conducted on taxonomic features, including the antenna, mouth parts, pronotum, elytra, scutellum, pygidium, legs, tarsal claw, sternum and male genitalia. Descriptions, illustrations and key to species of Scarabaeidae in Kasaragod were prepared. Based on the literature collected and by running taxonomic keys, the identification of the species was done. The total length, total width, and maximum width of adult specimens were measured. Species diversity and distribution map were prepared with the help of PAST software. The study explored 53 species belonging to 25 genera under eight subfamilies viz., Aphodiinae Leach, Cetoniinae Leach, Dynastinae MacLeay, Melolonthinae Leach, Rutelinae MacLeay, Scarabaeinae Latrielle, Sericinae Kirby and Orphninae Erichson. Melolonthid species were recognized under six genera viz., Anomalochela Moser, 1913, Apogonia Kirby, 1818, Holotrichia Hope, 1837, Leucopholis Dejean, 1833, Schizonycha Dejean, 1833 and Sophrops Fairmaire, 1887. The Sericinae species were associated with two genera Maladera Mulsant and Rey, 1871 and Selaserica Brenske, 1897. The Rutelinae species were recognized under five genera viz., Adoretus Laporte, 1840, Anomala Samouelle, 1819, Mimela Kirby, 1823, Parastasia Westwood, 1841, Popillia Serville, 1825. The subfamily Dynastinae is recognized into two genera viz., Alissonotum Arrow, 1908 and Oryctes Hellwig, 1798. The subfamily Scarabaeinae is associated with four genera viz., Catharsius Hope, 1837, Copris Geoffroy, 1762, Digitonthophagus Balthasar, 1959, Onitis Fabricius, 1798, Onthophagus Latreille, 1802. Four genera reported from subfamily Aphodiinae such as Rhyssemus Mulsant, 1842, Chaetopisthes Westwood and Aphodius Illiger, 1798. Single genus were reported from Cetoniinae and Orphniinae, viz., Heterorrhina Schoch, 1894 and Orphnus Macleay, 1819 respectively. Aphodiinae is the most abundant subfamily reported in Kasaragod district with the genus Rhyssemus. Among phytophagous subfamilies, maximum species belonged to the sub-family Melolonthinae. Among the melolonthinae beetles Apogonia ferruginea is reported as the most abundant species in Kasaragod. Based on the comparison of different diversity indices, mid lands exhibited highest genus richness. The value of Simpson-Yule Diversity index (D) was highest for mid lands which indicates mid lands supported maximum genera of white grubs. The value of the Shannon - Weaver Diversity index (H) were found to be highest for foot hills indicating the suitability of the lands to harbour a wide variety of scarab fauna. The highest evenness index (E) found to foot hills followed by high hills, coastal lands and mid lands shows that foot hills are more favoured for a large number of white grub species. The Berger Parker dominance index (d) for the species dominance found to coastal lands showed that coastal lands are less diverse and where one species completely dominated the community. The Kaipad land recorded no scarab beetles. Effect of weather parameters was found to non-significantly correlated with the emergence of white grubs.