Abundance of honeybees linked to lower number of wild bees

A first-time study on the interaction between different species of bees foraging in Maltese habitats, has revealed that a high visitation rate by honeybees has a negative impact on the abundance of wild bees.

Wild bees are generally solitary species who often nest below ground, while honeybees live in large colonies and are often domesticated in honey production. The Maltese honeybee, which lives in colonies, is a sub-species of the honeybee Apis Mellifera Ruttneri, and is endemic to the Maltese islands.

The study published in the scientific journal Xjenza is based on a dataset of plant-bee networks from 78 sites surveyed by study authors Mario Balzan and Leticia De Santis between April and June 2020, before the decimation of bee colonies by oriental hornets in 2022.

A total of eight habitat types – namely roadside grass strips, garigue, maquis, garden, steppe, sand dune, woodland, wetlands and agriculture fields – have been surveyed to ensure coverage of different habitats prevailing in Malta.

In the study, the presence of honeybees was strongly associated with agricultural habitats. Honeybees also used a wide range of floral resources that overlapped with those used by wild bees.

Previous data collected in 2019 had shown that Malta had a hive density of 12.86 hives per square kilometre. This was found to be significantly higher than the hive density recorded in other European countries which had an average of 4.2 hives per sq.km. A total of 105 bee species, most of which are wild bees, have been recorded from the Maltese Islands.

The new study, which recorded 2,610 plant-bee interactions involving 74 different flowers and plants, confirmed that honeybees are the most dominant species in this plant-bee network, performing 86.3% of all interactions with flowers and plants.

It is the Crown daisy that is the flower most visited by both wild bees and honeybees.

Honeybees also expressed a preference for the Mediterranean thistle and the wild artichoke. The Crown daisy attracted different wild bee groups and species and accounted for 10.2% of all plant-bee interactions and 32.7% of all plant-wild bee interactions.

This study also provides a first analysis of the impact of local and landscape habitats on the abundance and diversity of bees in the Maltese islands, with the intention of informing habitat management practices which benefit beekeepers and help in the conservation of the endemic Maltese honeybee, while also prioritising the conservation of wild bees.

The study shows that both the endemic Maltese honeybee and ground-nesting wild bees tend to be more present in agricultural habitats to the exclusion of other wild bees.

The study recommends a greater diversity of floral resources and nesting habitats in this habitat to cater for a wider range of wild bee groups and species.

On the other hand, grass strips along roads were found to attract a greater abundance of wild bees who lay their eggs above ground.

Roadside vegetation continued providing floral resources even after the removal of crops in agricultural fields at the start of the dry season. For this reason the proper management of road-side habitats is deemed important for the preservation of bee communities.

One of the recommendations made is to reduce the frequency of mowing these strips or lawns to less than twice a year.

The study provides the first evidence from locally-collected data of competition between honeybees and the wild bees of the Maltese islands.

The authors acknowledge the “high cultural value” of endemic honeybees and beekeeping, but they warn that the intensification of beekeeping “through an unplanned increase of apiaries” to boost pollination and honey production, may result in the loss of wild bees who also contribute to pollination.