Regular dorsal dimples onVarroa destructor– Damage symptoms or developmental origin?

Abstract

Adult females (n = 518) of Varroa destructor from Apis mellifera prepupae were examined by scanning electron microscopy without prior fluid fixation, dehydration and critical-point drying. Fifty-five (10.6%) mites had one (8.1%) or two (2.5%) diagonal dimples positioned symmetrically on the idiosoma’s dorsum. Where one such regular dorsal dimple existed per mite body, it occurred on the left or right side, equally. Mites with at least one regular dorsal dimple were 3.4% longer, but neither idiosomal width nor elliptical area differed significantly from mites lacking dimples. Dimple length was normally distributed in the population, and averaged 462 ± 9.2 μm (s.e.; n = 68 dimples). Internally, each regular dorsal dimple aligns with a series of obliquely-situated, dorso-ventral muscles in the opisthosoma. It is concluded that regular dorsal dimples are faults originating during mite ontogeny and should be considered separately from damage to Varroa destructor inflicted by honeybees or predatory arthropods.