Foodborne Transmission and Clinical Symptoms of Honey Bee Viruses in Ants Lasius spp

Abstract

Emerging infectious diseases are often the products of host shifts, where a pathogen jumps from its original host to a novel species. Viruses in particular cross species barriers frequently. Acute bee paralysis virus (ABPV) and deformed wing virus (DWV) are viruses described in honey bees (Apis mellifera) with broad host ranges. Ants scavenging on dead honey bees may get infected with these viruses via foodborne transmission. However, the role of black garden ants, Lasius niger and Lasius platythorax, as alternative hosts of ABPV and DWV is not known and potential impacts of these viruses have not been addressed yet. In a laboratory feeding experiment, we show that L. niger can carry DWV and ABPV. However, negative-sense strand RNA, a token of virus replication, was only detected for ABPV. Therefore, additional L. niger colonies were tested for clinical symptoms of ABPV infections. Symptoms were detected at colony (fewer emerging workers) and individual level (impaired locomotion and movement speed). In a field survey, all L. platythorax samples carried ABPV, DWV-A and -B, as well as the negative-sense strand RNA of ABPV. These results show that L. niger and L. platythorax are alternative hosts of ABPV, possibly acting as a biological vector of ABPV and as a mechanical one for DWV. This is the first study showing the impact of honey bee viruses on ants. The common virus infections of ants in the field support possible negative consequences for ecosystem functioning due to host shifts.

Keywords: Acute bee paralysis virus; Apis mellifera; Deformed wing virus; Lasius niger; Lasius platythorax; clinical symptoms; foodborne virus transmission.

Figure 1

Movement of individual ants (Lasius niger) from the two treatments that differed with regard to the feeding regime (controls = no virus, treatment = virus): (A) Overall movement of the ants estimated as centimetres crossed during 120 s; (B) The amount of time ants were not moving around in the arena; (C) Average speed seen over 120 s; (D) Distance covered during the first 10 s. A significant difference between the groups (linear mixed effect models, p < 0.05) is indicated by different letters (a, b).Furthermore, foragers of the treatment group were observed displaying conspicuous behaviour in the foraging arena. The impaired motions can be described as unnaturally slow movements followed by uncontrolled trembling or twitching motions as well as almost normal movements but with mostly immobile hind extremities (Figure 2).

Figure 2

QR code to access the video showing ants (Lasius niger) displaying clinical symptoms of Acute bee paralysis virus (ABPV) after experimental feeding with infected honey bee pupae (URL: https://www.youtube.com/watch?v=3bE_3Gl1Pp4&feature=youtu.be).

Figure 3

Colony size for the two treatments that differed with regard to the 10 week feeding regime (controls = no virus (N = 8), treatment = virus (N = 8) measured as the number of Lasius niger workers (A) and pupae (B) upon initiation of the experiment (July, 2016) and the change in the number of workers (C) and pupae (D) after 13 weeks. A significant difference between the groups (Student’s t-test, p < 0.05) is indicated by different letters (a, b).