The influence of relative humidity on egg hatch in Euseius filandicus, Typhlodromus pyri and Kampimodromus aberrans (Acari, Phytoseiidae).

The effects of different relative humidities (50%, 55%, 65%, 75%, 85% and 100% RH) on egg hatch were tested at 25 ± 1°C for three strains of Euseius finlandicus Oudemans, two strains of Typhlodromus pyri Scheuten and two strains of Kampimodromus aberrans Oudemans. At decreasing humidity, egg mortality increased earlier in K. aberrans than in E. finlandicus and T. pyri. E. finlandicus and T. pyri had similar humidity responses. Differences between strains within each species were small. RH50 values (relative humidity at which 50% of eggs hatch) were 50.4%, 52.4% and 53.1% for strains of E. finlandicus, 51.8% and 53.3% for strains of T. pyri, and 55.3% and 57.5% for strains of K. aberrans, respectively. Eggs of the Finnish E. finlandicus strain were most drought resistant (50.4% RH50), eggs of the French K. aberrans strain were most sensitive (57.5% RH50). The results are discussed in relation to the abundance of these species on certain plants and to the humidity responses of other phytoseiids. [ABSTRACT FROM AUTHOR]