Background and Objective
Biodiversity plays a crucial role in maintaining the balance and functionality of ecosystems. In agricultural systems, such as citrus orchards, assessing the diversity and population dynamics of terrestrial invertebrates — both pests and beneficial organisms — is essential for effective pest management and sustainable production. This study aimed to investigate the fauna, biodiversity indices, and seasonal population changes of soil-dwelling and foliage-inhabiting terrestrial invertebrates in two adjacent citrus orchards with different management regimes—one managed conventionally and the other abandoned—in Sari Country, Mazandaran Province, northern Iran.
Materials and Methods
The survey was conducted over 16 months from December 2019 to April 2021, in two separate citrus orchards planted with Japanese mandarin and Thompson orange, respectively. The managed orchard (13 ha) and the abandoned orchard (12 ha) were both located in the northern part of Goharbaran village at a similar altitude and under similar ecological conditions. Both orchards shared comparable canopy structure and plant physiology, thus minimizing the confounding effect of crop variety. Soil invertebrates were sampled using pitfall traps—30 traps in each orchard, totaling 60—installed at a depth of 15 cm beneath the tree canopy. Each trap consisted of a glass jar filled with a mixture of water and non-alcoholic beer. Traps were collected after 7 days, and sampling was repeated monthly. Invertebrates were identified and counted under a stereomicroscope. For canopy sampling, five trees were randomly selected in each orchard. From each tree, one 10-cm branch and five leaves were collected from four cardinal directions at a height of 1–1.5 meters, biweekly. During the fruiting period, similar procedures were used to collect fruit samples. All specimens were examined and recorded in the laboratory using a stereomicroscope. Biodiversity indices, including Shannon, Simpson, Margalef richness, and Pielou’s evenness, were calculated using PAST software.
Results
A total of 5,373 individual invertebrates were collected from both sampling methods. Among soil-dwelling groups, springtails (Collembola) showed the highest abundance, followed by beetles (Coleoptera), ants (Hymenoptera), and gastropods (Gastropoda). In the foliage samples, 902 individuals belonging to 18 species were identified. Hemiptera (365 individuals, 9 species) was the most diverse and abundant order, followed by Hymenoptera (219 individuals, 3 species) and mites (Acari) (169 individuals, 2 species). Common pests included citrus red mite (Panonychus citri), green citrus aphid (Aphis spiraecola), soft scale insects (Pulvinaria auranti), and the Mediterranean fruit fly larva (Ceratitis capitata). Notably, the brown garden snail (Caucasotachea lencoranea) and other mollusks were also frequently encountered. Springtails were more abundant during colder months, while ants and mites peaked in warmer periods. The highest Shannon index (2.34), Margalef richness (2.73), and Pielou’s evenness (0.93) were recorded in the managed orchard in November 2020, whereas the highest Simpson index (0.87) was observed in December 2020. In contrast, the abandoned orchard showed peak values for Shannon (2.08) and Simpson (0.85) indices in April 2021, Margalef richness (2.22) in February 2020, and Pielou’s evenness (0.94) in November 2020. Regarding foliage-inhabiting invertebrates, the managed orchard had maximum biodiversity in September 2020 (Shannon = 2.12, Simpson = 0.87, Margalef = 2.05) and December 2020 (Pielou = 0.98). The abandoned orchard had the highest values in August 2020 (Shannon = 2.26, Simpson = 0.89), September 2020 (Margalef = 2.68), and November 2020 (Pielou = 0.98), but this difference was not statistically significant.
Discussion
The results indicated that the abandoned orchard supported higher overall biodiversity compared to the managed one. This may be due to the absence of tillage and reduced chemical inputs, which help preserve soil structure and protect beneficial organisms. Frequent tillage in the managed orchard likely disrupted soil fauna habitats, resulting in reduced springtail abundance. Additionally, improper pesticide use and failure to observe pre-harvest intervals may have negatively impacted beneficial arthropods, thereby increasing pest resistance. Seasonal trends in the dominance of taxa also reflected environmental influences, particularly temperature and orchard management practices. Carabid beetles (Carabidae), known for their predatory activity, were frequently recorded in the abandoned orchard, suggesting they may offer pest suppression comparable to chemical controls. Overall, the diversity and abundance of both beneficial and pest invertebrates under different temporal and ecological conditions highlighted their potential as indicators of environmental health and sustainable orchard management. The findings underscore the importance of ecologically based pest management practices that conserve biodiversity and ecosystem services in citrus production.