Management of onion thrips continues to be a high pest priority for Wisconsin onion growers. In 2006 the hot and dry conditions experienced in mid-summer led to increased populations that were very difficult to control in some areas. Furthermore, many of the earlier registered products for control of onion thrips are loosing control efficacy. Onion thrips insensitivity to λ -cyhalothrin (Warrior®) is suspected in Wisconsin similar to that which has been proposed in Ontario, Canada (Allen et al., 2005) and in New York populations using a thrips insecticide bioassay system (TIBS) (Shelton et al., 2003). Local insensitivity to Lannate® may also be occurring with increasing leaf damage following foliar applications and only ‘fair’ control of thrips populations. As a result, onion thrips management should be a top priority along with the potential for onion thrips to spread Iris yellow spot virus (IYSV) (Gent et al., 2004). An improved understanding of the ecology and management of onion thrips on a broad scale is essential to develop methods of control for this pest and to develop effective resistance management plans.