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.Key to captions a ascending limb of peritrematic groove - c hollow (haemocoel) core of peritreme - d descending limb of peritrematic groove - e endocuticle - f flange of the inner stigmatic orifice - g peritrematic groove - i funnel of inner stigmatic orifice - k circum-spiracular pocket at base of peritreme - 1 peritrematic slit - m micropapillae - n fringe of marginal setae - o outer stigmatic orifice (=stigma) - p emergent peritreme - r rough integument at bases of leg coxae - s stigmatic atrium - t tracheal atrium - u outer lip of outr stigmatic orifice - v inner lip of outer stigmatic orifice - x tracheal trunks - z thick cuticle of peritrematic groove - 1,2,3,4 numbers of legs or leg coxae