Insecticidal Toxicities of Three Main Constituents Derived from Trachyspermum ammi (L.) Sprague ex Turrill Fruits against the Small Hive Beetles, Aethina tumida Murray

Small hive beetle (Aethina tumida Murray), indigenous to Africa, has spread to other parts of the world where has become a threat to the honeybee industry. In the present study, insecticidal properties (contact, fumigant, and repellent toxicities) of three main constituents derived from Trachyspermum ammi (L.) Sprague ex Turrill fruits essential oil were evaluated against adult small hive beetles under laboratory conditions. The Hydrodistillation of T. ammi fruits, grown in Ethiopia, yielded a pale yellow essential oil (3.5% v/w) with a strong aromatic odor. Analyses by gas chromatography-mass spectrometry identified twenty-two compounds that accounted for 98.68% of the total essential oil. The essential oil was dominated by monoterpenoids, comprising γ-terpinene (32.72%), p-cymene (27.92%), and thymol (24.36%). The essential oil showed strong contact and fumigation toxicities against the small hive beetle adults, with a LD₅₀ value of 66.64 µg/adult and a LC₅₀ value of 89.03 mg/L air, respectively. Among the main constituents, thymol was the most toxic component found in both contact (LD₅₀ = 41.79 µg/adult) and fumigation (LC₅₀ = 52.66 mg/L air) toxicities. The other two components, γ-terpinene and p-cymene, were less effective in both contact and fumigant toxicities testing. The results showed that T. ammi essential oil and thymol could serve as potential alternatives to synthetic insecticides for the control of small hive beetle adults.

Global warming promotes biological invasion of a honey bee pest

Climate change and biological invasions are two major global environmental challenges. Both may interact, e.g. via altered impact and distribution of invasive alien species. Even though invasive species play a key role for compromising the health of honey bees, the impact of climate change on the severity of such species is still unknown. The small hive beetle (SHB, Aethina tumida, Murray) is a parasite of honey bee colonies. It is endemic to sub-Saharan Africa and has established populations on all continents except Antarctica. Since SHBs pupate in soil, pupation performance is governed foremost by two abiotic factors, soil temperature and moisture, which will be affected by climate change. Here, we investigated SHB invasion risk globally under current and future climate scenarios. We modelled survival and development time during pupation (=pupal performance) in response to soil temperature and soil moisture using published and novel experimental data. Presence data on SHB distribution were used for model validation. We then linked the model with global soil data in order to classify areas (resolution: 10 arcmin; i.e. 18.6 km at the equator) as unsuitable, marginal and suitable for SHB pupation performance. Under the current climate, the results show that many areas globally yet uninvaded are actually suitable, suggesting considerable SHB invasion risk. Future scenarios of global warming project a vehement increase in climatic suitability for SHB and corresponding potential for invasion, especially in the temperate regions of the Northern hemisphere, thereby creating demand for enhanced and adapted mitigation and management. Our analysis shows, for the first time, effects of global warming on a honey bee pest and will help areas at risk to prepare adequately. In conclusion, this is a clear case for global warming promoting biological invasion of a pest species with severe potential to harm important pollinator species globally.