Comparative influence of temperature on development and biological control of two common vineyard pests (Acari: Tetranychidae)

We studied the effects of temperatures from 10 to 40 °C on development of the Pacific spider mite, Tetranychus pacificus (McGregor), and the Willamette spider mite, Eotetranychus willamettei McGregor (Acari: Tetranychidae), feeding on grape foliage. In addition, we investigated the influence of temperatures from 10 to 37 °C on development of the western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae), feeding on T. pacificus and evaluated the suitability of E. willamettei as prey for the predatory mite at 28 °C. Using a non-linear development rate model we estimated that the lower threshold for development of the three mites lay around 10 °C. T. pacificus was the most heat-resistant, with its upper threshold for development at 40.3 °C, followed by G. occidentalis at 37.1 °C and E. willamettei at 31.0 °C. T. pacificus developed significantly more rapidly than E. willamettei above 22.8 °C, whereas G. occidentalis developed significantly faster than either spider mite from approximately 11 to 36 °C. G. occidentalis developed 5% faster when feeding on E. willamettei than T. pacificus at 28 °C. These results confirm field observations linking E. willamettei damage to cooler, coastal vineyards and early in the season in inland vineyards, and T. pacificus infestations to hot vineyards in inland and coastal areas. Although T. pacificus seems to be more heat tolerant than G. occidentalis, additional information on temperature effects on adult life history details of the two mites is needed to fully evaluate G. occidentalis performance at high temperatures.