The carry-over effects of pollen shortage decrease the survival of honeybee colonies in farmlands.
Résumé
1. Many studies have reported honeybee colony losses in human-dominated landscapes.
While bee floral food resources have been drastically reduced over past decades in humandominated
landscapes, no field study has yet been undertaken to determine whether there is a
carry-over effect between seasonal disruption in floral resource availability and high colony
losses.
2. We investigated if a decline in the harvest of pollen by honeybees in spring affected managed
honeybee colony dynamics (brood size, adult population and honey reserves) and health
(Varroa mite loads and colony survival) throughout the beekeeping season.
3. A decline in pollen harvest was associated with a direct reduction in brood production,
leading to a negative effect on the adult population size later in the season, and lower honey
reserves before the onset of winter. Furthermore, the decline in pollen harvest negatively
impacted the health of the colony, resulting in higher Varroa mite loads and higher seasonal
and winter colony losses.
4. Early-warning signs of these carry-over effects were identified, showing that preferential
investment in honey reserves instead of brood production early in the season increased the
decline in pollen harvest and its associated carry-over effects.
5. Synthesis and applications. The results suggest that the decline in pollen harvest may have
been overlooked as a cause of pollen shortage and associated bee colony losses. Strategies to
avoid such losses in intensive farmland systems include (i) limiting or avoiding honey harvests
in spring, (ii) monitoring colonies for early-warning signals of colony failure and (iii) increasing
the amount of floral resources available through wise land-use management.