Essential oil from Eupatorium buniifolium leaves as potential varroacide

Beekeeping has experienced a great expansion worldwide. Nowadays, several conventional pesticides, some organic acids, and essential oil components are the main means of chemical control used against Varroa destructor, an ectoparasite that may contribute to the colony collapse disorders. Varroa resistance against conventional pesticides has already been reported; therefore it is imperative to look for alternative control agents to be included in integrated pest management programs. A good alternative seems to be the use of plant essential oils (EOs) which, as natural products, are less toxic and leave fewer residues. Within this context, a bioprospecting program of the local flora searching for botanical pesticides to be used as varroacides was launched. A primary screening (driven by laboratory assays testing for anti-Varroa activity, and safety to bees) led us to select the EOs from Eupatorium buniifolium (Asteraceae) for follow up studies. We have chemical characterized EOs from twigs and leaves collected at different times. The three E. buniifolium EOs tested were active against Varroa in laboratory assays; however, there are differences that might be attributable to chemical differences also found. The foliage EO was selected for a preliminary field trial (on an experimental apiary with 40 hives) that demonstrated acaricidal activity when applied to the hives. Although activity was less than that for oxalic acid (the positive control), this EO was less toxic to bees than the control, encouraging further studies.