Population Dynamics of Arthropods in New Caledonian Citrus Orchards

Aims: Agroecological infrastructures are central to the preservation of arthropod populations and ecosystem services associated. There is little data on the population dynamics of New Caledonian citrus orchards. Thus, this study focuses on the response of arthropods to four management methods in the orchard: conventional management, inter-row vegetated, row mulching and edge windbreaks.

Place and Duration of Study: This study was conducted in the village of La Foa in New Caledonia. It took place over three months, from the end of February to the end of May 2022.

Methodology: To collect the greatest possible diversity of insects, four complementary trapping methods were used: pitfall traps, yellow plates, Malaise traps and sweeping nets. Once collected, the trapped insects are then sorted and identified. The sorting is done with a binocular magnifying glass. Insects are identified using specific determination keys, documentation, or with the help of the Reference Collection of Terrestrial Invertebrates of New Caledonia - Xavier Montrouzier (CXMNC). When identification is not immediately possible, a morphotype number is assigned. For each species and morphospecies, a photograph is taken. Alpha and beta diversity was studied using rarefactions, Shannon index and Generalized Linear Models.

Results: A positive effect of agroecological infrastructures on insects’ abundance and diversity was recorded. In contrast, low arthropod abundances and diversities were presented in the orchard under conventional management (P < 0.001). Mulching management was the parameter showing the much higher insects’ abundance. Moreover, populations dynamics were generally correlated with the related infrastructures. Thus, windbreaks acted as ecological corridors and the inter-row vegetation as refuge habitats for beneficial insects.

Conclusion: These results demonstrate the damage of conventional agriculture on arthropod diversity in New Caledonian orchards. They also show that agroecological infrastructures can bring back insect biodiversity, especially with the mulching management.