Impacts of a biocontrol agent on invasive Ageratina adenophora in Southwest China: Friend or foe?

Classical biological control of invasive plants depends on the introduction host-specific natural enemies. Many enemies have provided successful control, but impacts herbivorous insects their hosts are highly variable and context dependent. Under some circumstances, overcompensation can even occur, with plant reproduction temporarily increasing rather than decreasing in response to herbivory. The stem-galling fly Procecidochares utilis has been widely introduced help Ageratina adenophora, a globally significant weed, its impact inconsistent places ineffective. Its galling is known stimulate production side branches under laboratory conditions. We examined abundance P. at four A. adenophora sites Southwest China that were invaded different times support densities insect. Stems galls more likely be branched produced capitula. Furthermore, seed numbers capitula from galled un-galled stems similar, resulted only slightly reduced weights. However, increase above-ground vegetative biomass associated branching less efficient capitulum relative growth. Clearly not providing effective biocontrol so far. In long term, may display competitive ability lower lifetime reproductive success, short term increases it generates suggest favouring host’s range expansion. agent dry area Hawii, understanding factors determine effectiveness represent major challenge for future.