Control of the invasive weedAmbrosia artemisiifoliawithOphraella communaandEpiblema strenuana

Ambrosia artemisiifolia L. is native to North America, and was unintentionally introduced into China in the 1930s, where it has become invasive. The two insect species Epiblema strenuana and Ophraella communa have been considered as biological control agents of A. artemisiifolia in China. The purpose of this study was to examine the control effect of O. communa + E. strenuana on A. artemisiifolia in the field. The mortality of A. artemisiifolia plants increased with time and increasing initial release densities of O. communa and/or E. strenuana in 2008 and 2009. The treatments of 0.53 O. communa + 0.53 E. strenuana per plant and 12 O. communa + 16 E. strenuana per plant at early (60–70 cm tall) and later (90–100 cm tall) growth stages could subsequently kill all plants prior to seed production in both 2008 and 2009. Thus, the two initial densities of the two insect species may be recommended when they are jointly used for biological control of A. artemisiifolia at the two growth stages. However, all or some plants could survive and bear seeds in any other treatment and in the non-treated control plots. This implies that biological control of A. artemisiifolia with the two biological control agents will be recommended in the areas invaded by A. artemisiifolia in China.