Seasonal variation in the lower thermotolerance of adult New Zealand flower thrips Thrips obscuratus (Crawford)

The ability of New Zealand flower thrips (NZFT) to tolerate cold temperatures was investigated. Thrips were collected from a range of natural sources in Central Otago over 2 years. Some adult NZFT (predominantly females) survived for up to 2 months on peach fruit at 0-1°C; LT50 = 35.4 days and LT99 = 70.7 days. Plant material containing NZFT was exposed for 24 h to -10, -7.5, -5, -2.5 and 0°C and NZFT mortality measured. Irrespective of the time of year when NZFT were collected, mortality was similar after 24 h at -2.5°C to that at 0°C (means = 4.6, 4.7%), but increased with decreasing temperature (mean mortality = 22.5% at -5°C, 66.3% at -7.5°C and 82.0% at -10°C). From -7.5°C downwards, responses to changes in temperature varied between seasons (P<0.01), with autumn adults being less cold-tolerant than those collected in spring. Central Otago winter temperatures would not have threatened the survival of NZFT over the study period.