Crassula helmsii: Biological control using herbivores
Overall effectiveness category No evidence found (no assessment)
Number of studies: 0
Background information and definitions
The introduction of a co-evolved herbivore from the area of origin of the invasive plant, which eats only the target plant species, could potentially provide sustainable control without affecting other native plants. However, C. helmsii has few reported natural enemies, and a biological control programme should consider consequences for closely-related, protected, native species, such as Crassula aquatica (Sheppard et al. 2006).
Some species of host-specific insects, such as chrysomelid and curculionid beetles, have been used as biological control agents of invasive aquatic weeds in several areas globally with some success (Gassman et al. 2006; see also ‘Water primrose Ludwigia spp. – Biological control using co-evolved, host-specific herbivores’). Mite species which parasitize plants (eriophyid mites) have also been used for biological control of invasive plants (Smith et al. 2010). These mites have high host specificity and negatively affect the host plants’ reproductive success, so could potentially limit the rate of spread of C. helmsii. The stem-mining fly Hydrellia perplexa has also been investigated as a potential biological control agent, although initial results suggest impacts on C. helmsii may be small (Shaw 2013, CABI 2014).
Grass carp Ctenopharyngodon idella is another herbivorous species used to control invasive freshwater plant species (see ‘Water primrose Ludwigia spp. – Biological control using co-evolved, host specific herbivores’). However, these fish are non-selective, and C. helmsii appears not to be a preferred food for this species (Dawson & Warman 1987).
CABI (2014) CABI Annual Report. Europe UK 2012. CABI, Egham, UK.
Dawson F.H. & Warman E.A. (1987) Crassula helmsii (T. Kirk) cockayne: Is it an aggressive alien aquatic plant in Britain? Biological Conservation, 42, 247-272.
Gassmann A., Cock M.J.W., Shaw R. & Evans H.C. (2006) The potential for biological control of invasive alien aquatic weeds in Europe: a review. Hydrobiologia 570, 217-222.
Shaw, R.H. 2013. Progress with weed biocontrol projects, CABI in the UK. June 2013. CABI, UK.
Sheppard A.W., Shaw R.H. & Sforza R. (2006) Top 20 environmental weeds for classical biological control in Europe: a review of opportunities, regulations and other barriers to adoption. Weed Research, 46, 93-117.
Smith, L., de Lillo E. & Amrine Jr. J.W. (2010) Effectiveness of eriophyid mites for biological control of weedy plants and challenges for future research. Experimental and Applied Acarology, 51, 115-149.