Onion thrips,Thrips tabaci(Thysanoptera: Thripidae), overwintering in South Auckland, New Zealand: the importance of the local bionomic data/temperature model and biosecurity implications

Onion thrips flights in winter and early spring 1999 were monitored in South Auckland using sticky traps and trap plants. A pair of yellow sticky traps and 10 ‘thrips-free’ onion pot plants per site were changed every 2 weeks. Thrips were detected on traps and plants in June, September and October. Sticky traps were the most reliable method for detecting thrips flights. Wild plants were inspected four times and revealed that thrips bred all winter. There was no diapause. Seedlings that had sprouted in mid July had second instar larvae by 4 October 1999. The nearest source was self-set plants in an adjacent field. Three published temperature models for onion thrips development were compared. Generation times were similar in summer, but very different in winter. The Texas model with minimum developmental threshold of 11.5 °C had the longest winter generation time and required a thrips flight by early August for second instar larvae to develop in the crop by 4 October, whereas the South Auckland model (threshold 8.7 °C) required flights by early September. Thrips flights were detected by traps in September but not August 1999. For cosmopolitan pests that are very variable genetically, it is important to generate local biological data. The biosecurity implications of this variability are discussed.