Abstract:

It is a dictum that Apis mellifera Linnaeus is innocuous in agricultural
ecosystems. This study provides the first record of A. mellifera as a significant
defoliator of Alnus species. Careful field observations coupled with microscopic
examination provided convincing evidence implicating A. mellifera as the cause of
leaf perforation on Alnus species in Uganda. Apis mellifera was observed foraging
selectively on young Alnus leaves and buds in search of a sticky substance,
apparently propolis. In so doing, the bee created wounds that enlarged and caused
tattering of Alnus leaves as they matured. Biological surveys indicated that the
damage was prevalent and occurred widely, particularly on Alnus acuminata Kunth
in Uganda. Incidence of the Apis mellifera damage on Alnus acuminata peaked in the dry season, with up to 90% of leaves emerging per shoot per month damaged, and was lowest in the wet months during peak leaf emergence. Apis mellifera leaf
damage was consistently higher on Alnus acuminata than A. nepalensis D. Don., on
saplings than mature trees, and on sun exposed than shaded leaves. The activity of
honeybees may be detrimental to the productivity of Alnus, yet the substance for
which the insect forages on Alnus is a resource with potential economic
importance.