Israeli Acute Paralysis Virus Associated Paralysis Symptoms, Viral Tissue Distribution and Dicer-2 Induction in Bumblebee Workers (Bombus Terrestris)

Although it is known that Israeli acute paralysis virus (IAPV) can cause bee mortality, the symptoms of paralysis and the distribution of the virus in different body tissues and their potential to respond with an increase of the siRNA antiviral immune system have not been studied. In this project we worked with Bombus terrestris, which is one of the most numerous bumblebee species in Europe and an important pollinator for wild flowers and many crops in agriculture. Besides the classic symptoms of paralysis and trembling prior to death, we report a new IAPV-related symptom, crippled/immobilized forelegs. Reverse-transcriptase quantitative PCR showed that IAPV accumulates in different body tissues (midgut, fat body, brain and ovary). The highest levels of IAPV were observed in the fat body. With fluorescence in situ hybridization (FISH) we detected IAPV in the Kenyon cells of mushroom bodies and neuropils from both antennal and optic lobes of the brain in IAPV-infected workers. Finally, we observed an induction of Dicer-2, a core gene of the RNAi antiviral immune response, in the IAPV-infected tissues of B. terrestris workers. According to our results, tissue tropism and the induction strength of Dicer-2 could not be correlated with virus-related paralysis symptoms.