Abstract
The efficiency of biological control agents is often affected by local conditions such as low relative humidity (r.h.). This is especially true for mites of the family Phytoseiidae, and particularly for their egg stage. A key issue in biological control is thus to assess the drought tolerance of phytoseiid species that are (or that will be) commercialized. In this study, we evaluated the egg hatching response to a humidity range for six species of Phytoseiidae, by assessing the relative air humidity and vapour pressure deficit (VPD) at which 50% of the eggs hatch: r.h.50 and VPD50. Typhlodromus athiasae Porath & Swirskii and Phytoseiulus longipes Evans (Argentinean strain) were the most drought-tolerant, with a r.h.50 of 43% (VPD50 = 18.2 hPa) and 43% (18.1 hPa), respectively. The most drought-sensitive species were Amblyseius swirskii (Athias-Henriot) (63%, 11.4 hPa), Phytoseiulus macropilis (Banks) (69%, 9.8 hPa), and Phytoseiulus persimilis Athias-Henriot (70%, 9.4 hPa). Neoseiulus idaeus Denmark & Muma and P. longipes (Chilean strain) showed intermediate responses with 49% (16.1 hPa) and 50% (15.9 hPa), respectively. These results were similar to what had been obtained for the same species by other authors. However, unexpected inter- and intraspecific differences uncorrelated to climatic conditions of the area of origin were observed. The possibility to localize species and/or populations that could be efficient as biological control agents under dry conditions is discussed