Intensification of the rice cultivation cycle reduces the diversity of aquatic insect communities in southern Brazilian irrigated rice fields

Fallowing represents a management practice that spares the land for at least one crop season. Reduction in the fallow period of rice-growing areas is, however, increasingly used to enhance grain production, and little is known about the possible effects of different extents of the fallow period on the aquatic fauna of irrigated fields. We assessed whether aquatic insect community structure differed among rice fields with different extents of fallow period and wetlands. Insects were collected in three rice fields with fallow season, three rice fields without a fallow season and three wetlands over the crop cycle in southern Brazil. Aquatic insect community structure markedly varied over the cultivation phases in wetlands and rice fields with and without fallow. While richness and abundance were lower in fallowing fields in the early phases of the cultivation cycle, richness was lower in rice fields without fallow at the end of the irrigated phase. Additionally, the composition of aquatic insects differed between wetlands and rice fields and between rice fields with different fallow periods, and showed reduced variation in rice fields without fallow. Our results indicate that changing fallowing extent can differently affect aquatic insect community structure in irrigated rice fields with respect to their successional trajectories over the cultivation cycle. Implications for insect conservation This study suggests that agricultural intensification (in terms of reduced extent of the fallow period) is associated with reduced diversity and biotic homogenization of aquatic insects compared to natural wetland and less-intensive agricultural practices in irrigated rice fields.

Automated summary

This study investigates the impact of different fallow periods and wetlands on the community structure of aquatic insects in rice fields. The results show that changing the fallow period can have varying effects on the community structure of aquatic insects in irrigated rice fields.