Add to ORKGWhat drives oystershell scale invasions? Connor Crouch Kristen Waring If you work with aspen in the American West, you may have heard of the invasive insect oystershell scale (OSS; Lepidosaphes ulmi). OSS was first observed causing aspen mortality in Arizona in 2016, and occurrences have since been observed in Utah, Nevada, and Idaho. One of the first questions we hear from practitioners about OSS-infested aspen is, “what’s causing these outbreaks?” This is an interesting question because OSS has been in North America for centuries and was documented on aspen in Arizona as early as the 1990s, but elevated incidents only recently began. Understanding what drives OSS invasions is a critical first step in developing management strategies