Odonata in rice agroecosystems: Testing good practices for their conservation

Abstract

Paddy systems have recently lost their original value as surrogate habitat for several wetland species due to rice farming intensification. Changes in water regimes largely compromised the survival of many aquatic organisms formerly abundant in rice fields, such as Odonata, inducing the introduction of new agricultural practices supposed to mitigate the negative impacts of intensive rice cultivation on biodiversity. For instance, the construction of a water retention structure (ditch) within paddies has been incentivized in Italy, in order to reduce the detrimental effects of drying periods on aquatic organisms. In this research, we investigate the effects of ditch occurrence and dimensions on Odonata diversity in rice fields, and furthermore we evaluate the response of these insects to vegetation height on paddy and canal banks, as an approximation of grass management intensity. Field surveys revealed that ditch occurrence may not be sufficient to improve the suitability of rice fields as breeding habitat for Odonata, especially for sensitive species. Paddies with ditches of larger dimensions supported more abundant adult populations than other field types, but no clear differences have been observed concerning larval stages. Conversely, the occurrence of a well-developed bank vegetation produced clear benefits for these insects in rice fields, while a not significant effect have been observed along irrigation canals. In order to achieve Odonata conservation in rice agroecosystems, together with the excavation of large ditches within paddies, the creation of a network of semi-natural wetlands should be encouraged, as well as the implementation of extensive grass management strategies on rice field and canal banks.