Onion (Allium cepa L.) is the favoured host of onion thrips (Thrips tabaci Lindeman). Wherever onion is planted, large numbers of onion thrips (more than 20 per plant) will likely appear in the crop at some stage. However, not long before the occurrence of peak numbers, onion thrips are almost undetectable. Where do the big numbers come from? To answer this question, seasonal patterns of onion thrips in onion were monitored in New South Wales (NSW) and South Australia (SA) during 2004–2005, growth potentials of onion thrips populations in onion during the period were analysed, and alternative hosts of onion thrips in surrounding weeds and non-onion crops were surveyed.

The contents of this Primefact include the following:

• Observed patterns
• Likely mechanisms
• Invasion sources
• Implications for management