Local and landscape drivers of population density and spatial variation of Bactrocera dorsalis and Bactrocera carambolae in Indonesian citrus orchards

Fruit fly infestations (Diptera: Tephritidae) pose a significant constraint to citrus production in Indonesia, yet current management practices often overlook the local and landscape factors. This two-year study aimed to investigate the differential effects of local and landscape drivers on the population density and within-orchard spatial variation of the two key pests, Bactrocera dorsalis and Bactrocera carambolae across nine citrus orchards in Malang Regency, Indonesia. Fruit flies were sampled using methyl eugenol traps and fruit rearing. Local factors measured plant age, pesticide frequency, elevation, and canopy cover. Landscape factors focused on the Class Area (CA) and Number of Patches (NP) of citrus orchards and semi-natural habitats. Temporal variation measured sampling year 2023 and 2024. Spatial variation of trap captures was quantified using its coefficient of variation (CV). Prior to model construction, multicollinearity among explanatory variables was assessed using the Variance Inflation Factor (VIF). Data were subsequently analyzed using Generalized Linear Models (GLMs) with a quasi-Poisson distribution. The study identified that B. dorsalis was highly dominant, while B. carambolae was less abundant. Results demonstrated that number of patches of citrus orchards (NP.citrus), significantly reduced the population density of both species. However, increased fragmentation significantly increasing spatial variation (CV) of B. carambolae. Local factors and semi-natural habitats did not show significant suppressive effects. These findings underscore that while fragmentation limits overall pest abundance, it simultaneously creates unstable population dynamics for B. carambolae. Sustainable management may prioritize landscape-wide monitoring and consider species-specific responses to habitat connectivity to more effectively suppress pest populations.