Sviluppo di acaricidi ecologici per un'apicoltura sostenibile

The honeybee (Apis mellifera) is widely recognized as one of the most crucial pollinators for maintaining biodiversity. However, in recent decades, honeybee populations have experienced a significant decline, primarily due to Varroa destructor, an ectoparasitic mite capable of causing colony collapse within months if left untreated. In addition to mechanical damage, Varroa acts as a vector for severe viral infections, further exacerbating honeybee losses. Current control measures, while partially effective, are increasingly limited by the development of resistance and environmental contamination. Among these, soft acaricides-natural compounds such as organic acids (e.g., oxalic acid) and essential oils (e.g., thymol, camphor, eucalyptol, and menthol)-are widely used to counteract this parasite. These substances offer advantages in efficacy and safety, with reduced risks of resistance development and hive product contamination compared to synthetic acaricides. However, a common limitation of soft acaricides is their dependence on frequent applications. Long-lasting formulations capable of sustaining active agent release for up to 21 days -the reproductive cycle of varroa- could address these challenges. This research focused on the development and evaluation of long lasting innovative formulations for the delivery of oxalic acid and essential oils. For oxalic acid, hydrophilic polymer-based gels incorporating xanthan gum and micronized silica were designed to ensure chemical stability and controlled release under acidic conditions. Preliminary in vivo evaluation studies showed a reduction on Varroa infestation levels (approximately 60%), with the added benefit of making the application easier. Additionally, silica sol-gel matrices were explored as an alternative delivery platform. These matrices achieved sustained release and demonstrated good in vivo efficacy (~70%), combining ecological safety with practical effectiveness. The results obtained are promising, and further in vivo experiments will need to be carried out. For thymol, silica sol-gel matrices were evaluated to develop a delivery system capable of releasing the compound over 28 days. Formulation studies identified triacetin as a promising cosolvent, mitigating thymol volatilization, and enabling sustained release under hive-like conditions. Initial in vivo trials demonstrated moderate efficacy, with environmental factors such as temperature variability and colony health identified as key determinants. In vivo studies show a good efficacy (~60%). Comparisons with the commercial product Apiguard® highlighted the advantages of single-application formulations. Mesoporous silica materials were also investigated for the controlled delivery of volatile compounds, including thymol, menthol, camphor, and eucalyptol. Silica-based carriers, particularly SilSol®, proved highly effective in maintaining thymol release. SilSol® emerged as the optimal carrier due to its cost-effectiveness, regulatory approval, and ability to stabilize thymol in its amorphous form. Field trials of thymol-loaded SilSol® formulations demonstrated efficacy (~75%) comparable to that of Apiguard®, with the added benefits of prolonged release from a single application, reduced volatilization losses, and strong acceptance by bees. The findings presented in this thesis contribute to the advancement of sustainable apicultural practices by offering innovative pest management solutions that prioritize both efficacy and ecological balance. These developments represent a significant step forward to ensure the health and resilience of honeybee populations.