Associations Between Landscape Quality, Pesticide Occurrence, and Adult-to-Brood Ratio in Honey Bee Colonies

Honey bee (Apis mellifera) colonies are exposed to multiple environmental stressors, including pesticide contamination and landscape changes, which may affect colony dynamics and colony condition. This study evaluated pesticide residue occurrence, landscape quality through the Agroecosystem Apibotanical Interest Index (AABI), and colony demographic structure across five contrasting agricultural systems in Uruguay using a comparative case-study approach. Pesticide residues were analyzed in multiple hive matrices, and residue occurrence was assessed using cumulative hazard quotients (HQ). Colony dynamics were characterized using population variables and the adult-to-brood ratio, associations were evaluated with generalized linear models. Pesticide diversity and cumulative HQ values were higher in intensively managed landscapes, particularly in horticultural and soybean systems, whereas forestry systems showed consistently low values. Residues were detected in all matrices, with greater diversity in wax and bee bread. Colony dynamics varied among landscapes, with more stable patterns in native forest systems. Demographic states based on the adult-to-brood ratio were consistently associated with colony demographic structure. We identified a significant negative statistical association between AABI and the demographic state defined by the adult-to-brood ratio, whereas cumulative HQ showed only marginal effects. Given the observational nature of the study and the multifactorial determinants of colony dynamics, this relationship should be interpreted as an observed pattern within the studied dataset rather than evidence of a direct biological effect of landscape quality on colony adult-to-brood ratio. Overall, the results suggest associations between environmental conditions and colony adult-to-brood ratio.