Optimum temperature and humidity for population growth of Chelifer cancroides that has potential for biocontrol of Varroa destructor in honey bee hives

The polyphagous pseudoscorpion predator Chelifer cancroides (Chelifer) has potential for biocontrol of the ectoparasite Varroa destructor (Varroa) of Apis mellifera honey bees. Their potential is greatest when Chelifers are actively breeding, which is dependent on temperature. Temperatures within bee hives vary from 36 °C at the brood centre of the colony to ambient at its periphery. To determine positions in the colony in which to place the Chelifer for their optimum population growth, the number of offspring from 15 male and 15 female Chelifers presented with abundant prey was assessed over 1 year at six fixed temperatures in incubators and at an ambient variable mean temperature of 14.7 °C (SD = 7.7) in a bee-less hive outside. At the fixed temperatures of 8, 16, 22, 26, 30, and 36 °C, 14, 50, 325, 378, 407, and 5 protonymphs were produced, respectively. At the ambient temperature, 29 live protonymphs were produced. The durations of protonymphs until maturity at these temperatures were also assessed in separate cages. The female protonymphs matured in 22, 16, 9, and 10 weeks to produce eggs, but only at the fixed 22, 26, 30, and 36 °C, respectively. Mortality of adults below a vapour pressure deficit (VPD) of 0.75 kPa was minimal but increased rapidly to 1.1 kPa, followed by a linear increase for higher VPD values. To achieve the temperatures for optimum population growth of Chelifer in a hive, Chelifer would need to be placed within the periphery of the brood, or if brood is not present, in the centre of the bee cluster.