Exploration for the Biological Control of Flowering Rush, Butomus umbellatus

• Main Authors: Hafliger, P, Leiner, R, Baan, C, Martins, A, Soukou, S, Sjolie, D, Tosevski, I, Hinz, H L
• Other Authors: CAB INTERNATIONAL DELEMONT (SWITZERLAND)
• Format: Text
• Language: English
• Published: 2015
• Subjects: Biology; *AQUATIC PLANTS; *INSECTS; CONTROL; DIPTERA; BIOLOGICAL CONTROL; BUTOMUS UMBELLATUS; FLOWERING RUSH; HOST-SPECIFICITY TESTS; REARING; WEEVILS; BAGOUS NODULOSUS; COLEOPTERA; Canada; Butomus umbellatus
• Online Access: http://www.dtic.mil/docs/citations/ADA618357; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA618357

Flowering rush (Butomus umbellatus) is a perennial aquatic plant of European origin that was introduced to North America as an ornamental over 100 years ago. It has developed into an aggressive invader of freshwater systems especially in the midwestern and western states of the USA and western Canada. Since no effective control methods are currently available, a biological control project was initiated in spring 2013 and CABI in Switzerland subcontracted to conduct surveys for natural enemies in the area of origin of flowering rush. This interim report summarizes data collected by CABI in 2014 until June 2015. Sites of flowering rush in northern Germany, where the rhizome-feeding weevil Bagous nodulosus is known to occur were revisited in 2014 and new sites were checked in Hungary, the Slovak Republic and Poland. A total of 236 adults were collected from eight different sites. We continued our efforts to improve rearing success with B. nodulosus. However, we are still experiencing high larval mortality and only a few adults emerged from plants to which larvae or ovipositing females had been transferred. We are currently trying different methods in order to further improve rearing success. Nevertheless we were able to set up 150 adults for overwintering on potted plants in a pond and in plastic cylinders filled with water. Overwintering on potted plants placed in a pond worked very well (80% survival). In 2014, we started setting up host-specificity tests under no-choice conditions with B. nodulosus. Of the ten test plant species offered, none was accepted for egg laying by female weevils, confirming the narrow host range of B. nodulosus. We will continue host-specificity tests in 2015. During a field trip to the Slovak Republic at the end of May 2015, we most probably found the second Bagous species described as monophagous on flowering rush, B. validus.