LAUSR

Simple Summary A decline in the number and diversity of pollinators has been observed worldwide. Various butterfly species are also threatened by extinction. One of the less studied reasons for the pollinator decline are pathogens, although it is known that they can be transmitted between cultivated and some wild pollinator species. The objective of our study was to determine whether pathogenic honeybee viruses can be transmitted to butterflies. Butterfly and bee samples from four locations in Slovenia were analyzed using the molecular method RT-PCR. We considered six bee viruses and found very low levels of four of them, i.e., acute bee paralysis virus (ABPV), black queen cell virus (BQCV), Lake Sinai virus 3 (LSV3), and Sacbrood bee virus (SBV), in the butterfly samples compared to the bee samples, although these viruses were present in large amounts in honeybees from the same locations. The results of our study indicate that butterflies are probably contaminated with bee viruses when they visit the same flowers as honeybees. Therefore, based on the very low viral load, we believe that butterflies are unlikely to be threatened by bee viruses and that they are not important as vectors of viral infection to other pollinators. Abstract Several pathogens are important causes of the observed pollinator decline, some of which could be transmitted between different pollinator species. To determine whether honeybee viruses can be transmitted to butterflies, a total of 120 butterflies were sampled at four locations in Slovenia. At each location, butterflies from three families (Pieridae, Nymphalidae, Hesperiidae/Lycenidae) and Carniolan honeybees (Apis mellifera carnica) were collected. The RNA of six honeybee viruses, i.e., acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus A (DWV-A), Sacbrood bee virus (SBV), and Lake Sinai virus 3 (LSV3), was detected by a specific quantitative method (RT-PCR). The presence of ABPV, BQCV, LSV3, and SBV was detected in both butterflies and honeybees. All butterfly and bee samples were negative for CBPV, while DWV-A was detected only in honeybees. The viral load in the positive butterfly samples was much lower than in the positive bee samples, which could indicate that butterflies are passive carriers of bee viruses. The percentage of positive butterfly samples was higher when the butterflies were collected at sampling sites with a higher density of apiaries. Therefore, we believe that infected bees are a necessary condition for the presence of viruses in cohabiting butterflies. This is the first study on the presence of pathogenic bee viruses in butterflies.