Mbaka, Samuel Musyoka2026-02-142026-02-142025-09-10http://repository.embuni.ac.ke/handle/123456789/4533Masters ThesisRisk assessment is a critical prerequisite for the introduction of non-native biological control agents, as it ensures that the benefits of pest management do not come at the expense of irreversible ecological damage and unintended non-target impacts. In the context of biological control, comprehensive risk evaluations integrate laboratory cold tolerance testing, host-specificity testing and ecological modeling to predict an agent’s establishment potential and its subsequent effects on native biodiversity and ecosystem balance. Amblydromalus limonicus and Iphiseius degenerans are targeted as biological control agents of various pests and phytophagous mites such as thrips and whiteflies. Knowledge about cold tolerance of non-native biological control agents is critical to avoid permanently establishing them in new temperate areas outside of their native range. The cold tolerance of the predatory mites, A. limonicus and I. degenerans, was investigated in the laboratory to assess their establishment potential in northern Europe, particularly Sweden. The lethal time of I. degenerans (the number of days until 100% mortality was reached) declined steeply from 5°C to 0°C and was almost zero at -5°C. The lethal time of A. limonicus did not differ between 5°C and 0°C, but was reduced at -5°C. For both species, LTime50 (the number of days until 50% of the mites died) was longer for fed than for unfed mites. The lethal temperature of A. limonicus (the temperature at which 100% mortality was reached) was -17.75°C, whereas most I. degenerans died at -8.5°C. LTemp50 (the temperature at which 50% of the mites died) was lower for A. limonicus (-9.8°C) than for I. degenerans (-0.1°C). Complementing the cold tolerance assessments, bacterial communities within both mites were profiled across selected low and subzero temperatures. Both mites, were dominated by Firmicutes (most abundant phylum), Actinobacteria Bacteroidetes and Proteobacteria and the order Bacillales was consistently dominant consistently prevalent. Notably, A. limonicus displayed higher microbial diversity at -5°C, as indicated by Shannon index 3.01 which might confer additional adaptive advantages under cold stress. Collectively, the data support a robust risk assessment framework for these non-native biological control agents. The enhanced cold tolerance of A. limonicus signals a significant risk regarding its potential establishment in temperate regions such as Sweden, where it might persist and affect non target species and ecosystem dynamics. However, the observed lower cold tolerance of I. degenerans suggests that its survival through Swedish winter is unlikely, thereby reducing its establishment risk.enAmblydromalus LimonicusIphiseius DegeneransThesis