Egg hatching response to a range of air humidities for six species of predatory mites

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.

Efecto de la humedad relativa en la viabilidad de huevos de Neoseiulus sp. y Proprioseiopsis iorgius (Acari: Phytoseiidae) en condiciones de laboratorio

“…La HR 50 es a menudo discutida debido a su relación directa con la humedad relativa ambiental, en cambio la VPD 50 es dependiente de la temperatura, lo que permite comparaciones estandarizadas (Ferrero et al, 2010).…”

“…Uno de estos factores, la humedad relativa, afecta directamente sobre la supervivencia de los huevos de los fitoseidos (Walzer et al, 2007;Ghazi y Amano, 2016). Es un gran desafío encontrar depredadores tolerantes a la baja humedad relativa, especialmente para los cultivos donde la humedad es a menudo por debajo del 50-60%, lo que ha sido considerado como un límite para el desarrollo de muchos de los ácaros depredadores (Ferrero et al, 2010). En los estudios biológicos, las condiciones del vapor de agua se expresan comúnmente como humedad relativa (HR; %), que es el porcentaje de la presión de vapor [PV; Pa (Pascales)] en la presión de vapor saturada (PVS; Pa) a una temperatura del aire, o como un déficit de la presión de vapor (DPV; Pa) que es la diferencia entre PVS y PV.…”

“…La eficiencia de los controladores biológicos es a menudo afectada por condiciones locales tales como la humedad relativa baja. Esto es especialmente cierto para ácaros de la familia Phytoseiidae y particularmente para sus huevos (Ferrero et al, 2010). La tolerancia de los huevos a una baja humedad relativa en la familia Phytoseiidae puede relacionarse con el ambiente en el que han evolucionado sus especies (Negm et al, 2014).…”

Seasonal climatic variations influence the efficacy of predatory mites used for control of western flower thrips in greenhouse ornamental crops

“…Amblyseius swirskii are considered a drought sensitive mite species, as egg hatching for mites is largely related to humidity levels, with a higher egg hatch rate in more humid conditions (Ferrero et al, 2010). Humidity levels can interact with temperature to affect the level of efficacy of natural enemies in greenhouses (Heinz et al, 2004).…”

“…They suggested that this success was due to increased juvenile survival and development rate when provided a mixed diet. As this mite originates from the Mediterranean basin, mostly found in humid coastal areas, A. swirskii prefer high temperatures and have a critical RH limit of ~70%, anything lower may cause their eggs to desiccate (de Moraes et al, 2004;Ferrero et al, 2010;Porath & Swirski, 1965). Buitenhuis et al (2010a) recently discovered that A. swirskii does not disperse well when applied to separated plants.…”