A paper published in the journal Biological Control showed that flower-feeding weevils can be effective biocontrol
agents by reducing the number of flowers, fruits and seeds that the invasive tree Bugweed (Solanum mauritianum) produce. The
research, conducted by C·I·B PhD student Blair Cowie, and C·I·B Core Team Member Prof Marcus Byrne, at the
University of the Witwatersrand, assessed the impact of the flower-bud feeding weevil, Anthonomus santacruzi, on fruit production in
Bugweed, and the role of the weevil as an indirect pollinator.
Adult weevils spend most of their lives on and around Bugweed inflorescences, feeding on the flowers, particularly the
anthers (pollen), petals and buds. This results in the deformation of the flowers or premature shedding of flowers and buds from the
inflorescence. Previous studies have shown that Bugweed is self-compatible, like many invasive trees, but high levels of self-pollination
can often have negative effects of inbreeding.
Results from this study showed that the flower-feeding weevils reduced the number of flowers, fruits and seeds that the
Bugweed produced. The study further showed that by damaging the flowers, the weevils deter visits from pollinators, such as bees, and more
interestingly may increase the likelihood of self-pollination. Self-pollination results in the production of smaller Bugweed fruits with
fewer seeds, with reduced viability.
“This research suggests that in areas where the weevils are well established, they serve to limit the fruit and
seed production as well as facilitate the self-pollination and subsequent inbreeding of Bugweed. Although these findings show great promise
towards the biocontrol of Bugweed in South Africa, itís likely to be a long term game, given the widespread and persistent invasions of this
tree” says Blair Cowie, lead author of the paper and PhD student. He adds that “future fieldwork will assess the
contribution of this weevil to self-pollination in Bugweed populations.”
The flower-bud feeding weevil, Anthonomus santacruzi, is responsible for reductions in both the fruit
and seed set of Bugweed. Whilst increases in self-pollination, due to this weevil, decrease the treeís seed viability.
(Graphic by Blair Cowie)
For more information, contact Blair Cowie at firstname.lastname@example.org
Read the paper in Biological Control
Cowie, B.W., Witkowski, E.T.,
Byrne, M.J. and Venter, N., 2017. A villainous hero: Does the biological control agent, Anthonomus santacruzi, pollinate its target
weed, Solanum mauritianum? Biological Control 105: 79-85. doi: 10.1016/j.biocontrol.2016.11.012