Diversity of Yala season diurnal ant community in two selected rice fields in the Wet Zone of Sri Lanka

Abstract

Studies on the ant communities of Wet Zone rice fields in Sri Lanka are scarce and the present study was conducted to determine the diversity and species composition of ants throughout Yala season. Worker ants were sampled within two, almost similar, rain-fed rice fields (18 x 20 m) in Mahadarawa, Gampaha District from February to September in 2017 encompassing post-harvest, seedling, tillering, flowering and mature grain stages. In each rice field, pitfall trapping (20), honey baiting (20) and hand collection (15) were employed along a 20 m line transect during daytime. The collected ants were preserved in 85% ethanol and identified to the possible taxonomic levels in the laboratory using the relevant references. Air temperature and light intensity varied between 32-360C and 14478-19983 Lux m-2, respectively. Eleven ant species, Anochetus graeffei Mayr, Anoplolepis gracilipes Smith F., Camponotus compressus Fabricius, Carebara diversa Jerdon, Diacamma rugosum Le Guillou, Meranoplus bicolor Guerin-Meneville, Monomorium floricola Jerdon, Odontomachus simillimus Smith F., Paratrechina longicornis Latreille, Tapinoma melanocephalum Fabricius and Tetramorium walshi Forel in 11 genera of 4 subfamilies, Dolichoderinae, Formicinae, Myrmicinae and Ponerinae were recorded from the two rice fields. The most speciose subfamily was Myrmicinae whereas Dolichoderinae contained only a single species. Species richness observed for seedling stage and post-harvest stage-2 was 9, while 11 species were observed on the other occasions. Higher Shannon-Wiener Diversity index value (H’= 2.093) was observed for tillering stage than that of the seedling stage (H’= 1.764). The highest mean percentage frequency of occurrence was observed for C. compressus followed by T. melanocephalum while A. graeffei had the lowest value. Significantly higher frequencies of C. compressus and T. melanocephalum were observed (Chi square test, p<0.05) at the ‘Field 1’ and ‘Field 2’ on all occasions. A diverse ant community consisting of 9 permanent inhabitant species occurred at the two fields irrespective of the presence of both wet and dry conditions. Carebara diversa was a nuisance to farmers because the workers carried away germinated rice seeds from the paddy fields. It appeared that O . simillimus was a predator of the rice pest, Gryllotalpa orientalis Burmeister (Oriental mole cricket).