Fig 1.
Experimental plan of the study.
a) Test for experimental trigger of TGIP, and b) test for natural occurrence of TGIP.
Fig 2.
Brood survival probabilities when queens were experimentally exposed or not exposed to Melissococcus plutonius.
Survival profiles of brood reared in vitro experimentally inoculated with M. plutonius on the day of grafting or non-inoculated during the years 2019 and 2020. Survival profiles of brood are displayed according to their queen’s exposure status (non-exposed, exposed, or boosted) and the rearing period (pre- and post-exposure). Grey arrows represent the day of larval exposure to M. plutonius or to non-inoculated diets. Different letters indicate groups of treatments that differed significantly (Cox mixed-effects model, p < 0.05). Survival curves grouped by vertical bars were not significantly different (Cox mixed-effects model, p > 0.05).
Fig 3.
Brood production in colonies headed by queens experimentally exposed to Melissococcus plutonius.
Proportional changes in brood surface area observed in colonies between the time of queen exposure and three weeks post-exposure in 2019 and 2020. Black dots and bars represent the mean and standard deviation of each group, respectively. Circles represent the individual data points.
Fig 4.
Survival probabilities of the brood from queens non-exposed or naturally exposed to EFB.
Survival profiles of in vitro reared brood experimentally inoculated with Melissococcus plutonius on the day of grafting and the non-inoculated brood. Survival profiles of brood are displayed according to their queen’s exposure status (non-exposed and naturally exposed). Grey arrows represent the day of feeding with diet inoculated with M. plutonius or a non-inoculated diet. Different letters indicate treatments that differed significantly (p < 0.05) based on the Cox mixed-effects model. Survival curves grouped by a vertical bar on the right are not significantly different as per the Cox mixed-effects model (p > 0.05).
Table 1.
Cox mixed-effects model of survival of inoculated and non-inoculated larvae produced by non-exposed queens from healthy colonies and by Melissococcus plutonius exposed queens from EFB-diseased colonies.