Cultivation of domesticated rice influences arthropod diversity and community composition in the Mekong Delta, Vietnam

Background/Question/Methods

Although it is well established that biodiversity is important for sustainable food production, there is limited knowledge on how the cultivation of domesticated crops shapes arthropod diversity. Wild crop relatives are important for conservation not only for their genetic diversity, but also in terms of their support of arthropod food webs that control herbivorous insect pests. In order to determine the relative biodiversity conservation value of wild and cultivated rice, it is important to determine how arthropod diversity and community composition may differ between wild and cultivated rice. We examined how rice cultivation (domestication, tillage, insecticides) and season (dry vs. wet) influenced arthropod diversity and community composition. We used a modified leaf blower to sample in wild and cultivated rice fields in the Mekong Delta of Vietnam. We also sampled in a subset of farms that did not spray insecticides for pest control. The arthropods were identified to the lowest taxonomic level possible, and the majority of the samples were identified to the genus level. The arthropod samples were counted and classified by feeding guild. We compared wild and cultivated rice fields to determine how they differed in rarefied species richness, community composition, and relative guild abundance.

Results/Conclusions

We found that cultivated rice fields supported about 50% less species than wild rice fields, and losses in species richness ranged from 50-90% across all of the major phytophagous or predatory taxa. Although a large proportion of the arthropod assemblage was shared between wild and cultivated rice, arthropod community composition was quite different between wild and cultivated rice fields. A large number of taxa contributed to the dissimilarity between wild and cultivated rice fields, suggesting cultivation has a widespread impact across many taxa. Predators and parasitoids were the most abundant during the dry season in wild rice than in cultivated rice during the dry or wet season. Herbivore densities were similar in wild and cultivated rice during the dry season, but they were less abundant on wild rice during the wet season. Neither season nor habitat influenced the densities of detritivores, but aquatic predators were more abundant during the dry season. This study provides direct evidence that large scale losses of species richness and changes in arthropod community structure are associated with the cultivation of domesticated rice.