Effect of population density of the Azolla weevil (Stenopelmus rufinasus) on the surface cover of the water fern (Azolla filiculoides) in the UK

• Published in: BioControl (Dordrecht, Netherlands) Vol. 63; no. 2; pp. 185 - 192
• Main Authors: Reeder, R. H., Bacon, E. T. G., Caiden, M. J., Bullock, R. J., González-Moreno, P.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.04.2018; Springer Nature B.V
• Subjects: Agriculture; Animal Biochemistry; Animal Ecology; Aquatic plants; Augmentation; Azolla filiculoides; Behavioral Sciences; Biological control; Biomedical and Life Sciences; Curculionidae; Entomology; Experiments; Ferns; Floating plants; Herbivory; Life Sciences; Plant Pathology; Population density; Stenopelmus rufinasus; Stocking; Summer; United Kingdom > UK; Herbivory; Aquatic insect; Biological control; London Wetland Centre; Population density
• ISSN: 1386-6141; 1573-8248
• DOI: 10.1007/s10526-017-9861-5

Azolla filiculoides Lamarck (Azollaceae) (water fern), is an invasive floating macrophyte capable of rapid growth leading to the complete coverage of water surfaces. The North American weevil Stenopelmus rufinasus , Gyllenhal (Coleoptera: Curculionidae) is a biological control agent that has become naturalised in the UK. To determine the effects of the weevil on A. filiculoides in ‘semi-controlled’ conditions, weevils were introduced at four stocking densities into outdoor floating tanks containing A. filiculoides . The introduction of weevils at all densities resulted in a significant decline in percentage cover of A. filiculoides compared to the control. Increasing weevil stocking density resulted in a more rapid reduction in the area of green A. filiculoides . The highest stocking density of 400 weevils per m 2 caused complete kill within a month of introduction. The UK summer provides conditions that are suitable for weevil reproduction and herbivory, and even the lowest stocking density of weevils tested (100 weevils per m 2 ) can have a substantial impact on the surface cover of A. filiculoides . Although the weevil is effective in summer, augmentation is required annually for reliable control.