Population dynamics of Jaapiella ivannikovi, a gall midge introduced for biological control of Russian knapweed

The gall midge Jaapiella ivannikovi was introduced from Uzbekistan to North America in 2009 for biological control of Russian knapweed, an invasive plant of western rangelands.  We have been monitoring the population dynamics of the midge weekly at a site in central Wyoming for the past three years.  Newly formed galls have been observed from late May-August with a peak in early July.  Midges emerge from galls two to three weeks after first observation.  Gall numbers have increased at the site but because Russian knapweed ramets (shoot) numbers have increased more rapidly than galls, the percentage of ramets attacked has declined at the site.