The respiratory system of the femaleVarroa jacobsoni (Oudemans): its adaptations to a range of environmental conditions

The morphology of the respiratory system of the femaleVarroa jacobsoni (Oudemans, 1904) is described. The mobile, appendage-like, emergent peritreme may be ‘raised’ to lie against the ventral integument or ‘lowered’ between the third and fourth pair of legs. It is ‘raised’ when the mite is submerged in the liquid food of the host's brood chamber, where respiration occurs via an external plastron, formed by an airfilm trapped between the rough cuticle of the ventral integument and the retracted legs. The peritreme is also raised when the mite is outside the hive in sub-saturated air, to reduce water vapour transpiration, and it is ‘lowered’ in the carbon-dioxide-rich and water-saturated hive atmosphere, where it facilitates rapid removal of carbon dioxide. Thus gaseous exchange in the female mites may be adjusted by the position of the peritreme.