Larvae are legless, curved and are whitish to pink or orange. Larvae approximately 2 mm long when mature. Adults are medium to dark brown with transparent wings, long legs and large eyes. Their bodies are about 2 mm long, with males measuring slightly under 2 mm and females slightly longer.
These midges prefer new shoots and lateral shoots for egg laying. Fused leaves (“rosette” galls) and grey – silver appearance due to webbing or hairs on new shoots of Russian knapweed indicates their presence.
On average, adult males live less than a day and females 2-3 days after they emerge in the spring. Eggs are laid on shoot tips. Larvae feed within the gall among silky webs (hairs). Larvae go through three instars before pupating. They overwinter as pupae, but may have more than one generation per year. In their native Uzbekistan, they may have as many as four generations per year each lasting approximately one month.
Galls result in stunted growth and plant stress, limiting growth, flowering and seed production.
Currently, insects are available in Montana through a limited number of sources. The Montana Biocontrol Coordinator will share the contact information for these sources with interested parties.
A native of Uzbekistan it seems to thrive best in disturbed and -irrigated or moist areas due to resulting new growth of knapweed plants. Grazing by wildlife or livestock may impact populations when the midges are at low levels. This agent is still being monitored for effectiveness, however, it is established in several sites in MT and research in WY suggests it can limit seed production by 91% and reduce above ground biomass by 34%.
Using the Agent
The midges are best collected as mature galls from affected plants; as sweeping is difficult and can damage the delicate adults. Galls can either be placed directly in the infested area throughout the growing season according to specific protocols or maintained indoors for careful release of adults after emergence. Mowing the infected site prior to releasing insects may increase new shoots, for galling later in the season. . However, this may not be effective at dry sites where regrowth is limited by moisture. From 50-100 galls should be released to begin establishment efforts. Success should be monitored by looking for galls on Russian knapweed plants in current and subsequent years after release.
Due to the lack of knowledge regarding establishment and impact they should not be relied on as a sole strategy for managing Russian knapweed on a landscape level. They are best used in tandem with other management strategies including additional biocontrols, chemical and mechanical methods if eradication is your goal and to reduce spread while insects are establishing. Consult your local weed district or Extension Service for Russian knapweed management advice.
Winston, R., C.B. Randall, R. D. Clerck-Floate, A. McClay, J. Andreas, M. Schwarzlander. May 2014. Field Guide for the Biological Control of Weeds in the Northwest. http://www.ibiocontrol.org/westernweeds.pdf