Seasonal fluctuation, phenology and turnover of chafer assemblages : insight to the structural plasticity of insect communities in tropical farmlands

Studies on chafer assemblages were conducted on two farmland sites in the Terailowland of Nepal (200 m above sea level) using light traps. During the course ofa 2-year field monitoring program, a total of 4503 specimens was captured andan unexpectedly high number of syntopically co-occurring species was found: 52from Gunganagar (GN) and 36 from Gaindakot (GK), respectively. Highest speciesabundances and species numbers were found during April and May.2 Species occurrence was strongly correlated with air temperature and the maximumsoil temperature, at least during the pre-monsoon season. However, assemblagestructure from the two sites showed significant qualitative and quantitativechanges seasonally, as well as from 1 year to the next. Turnover rates betweenadjacent months were in the range 26 – 62% (GN) and 37 – 70% (GK), whereas theturnover from 2004 to 2005 was 25.8% (GN) and 21.4% (GK) respectively.3 When only dominant and subdominant taxa are considered, the seasonal changein species composition was even more striking.4 Strong fluctuation in chafer assemblage over time suggests: (i) a possible influenceof patchy habitat types and soil working on seasonal assemblage structureand (ii) colonization of suitable habitats (fields) in great part by chance.