Potential impact and non-target effects of Gallerucida bifasciata (Coleoptera: Chrysomelidae), a candidate biological control agent for Fallopia japonica
A pre-release evaluation of a potential biological control agent is designed to estimate the impact the
agent will have on the target in the introduced range, and whether the agent poses an acceptable level
of risk to biodiversity. Here, we present an evaluation of the Asian leaf-beetle, Gallerucida bifasciata, a
potential biological control agent for Japanese knotweed, Fallopia japonica. First we tested the impact of
different larval and adult densities on the plant under laboratory conditions. After six weeks, the biomass
of F. japonica was 15% or 28% that of control plants if larvae or adults were added, with levels of damage
plateauing quickly with increasing insects densities. High fecundity and larval density dependence means
that this agent could substantially and quickly suppress plant growth, although this damage only occurs
early in the season, allowing F. japonica time to compensate. Second, following on from general host-specificity
trials, we investigated potential non-target effects on the commercially important plant buckwheat,
Fagopyrum esculentum, in more depth. The leaf-beetle showed some minor adult feeding on F. esculentum
in choice trials, and in no-choice trials the leaf-beetle was able to complete its life cycle and sustain a population
on F. esculentum, albeit causing lower levels of damage than on F. japonica. This suggests that if the
beetle dispersed to areas where F. japonica is not present, it might colonise F. esculentum. Therefore,
despite potentially being an effective agent, that the risk of non-target feeding is unacceptably high