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The western honey bee (Apis melliferaL.) is the most globally used managed pollinator species, but it can have limited pollinating activity on nectariferous crops displaying anthers isolated from stigmas, i.e., when anthers are spatially or temporally separated from stigma within or between flowers. We supplemented honey bee colonies with pollen in the combs or in paste form laid on top of the hive frames to test if these treatments could reduce their pollen foraging and increase their pollinating activity in a monoecious and nectariferous cultivar of cantaloupe melon (Cucumis meloL.), in comparison with control colonies not supplemented. We recorded the pollen forager density per flower, the number of pollen grains deposited per stigma and their resulting fruit set, seed set and fruit mass, before and after the colony pollen supplementations. The number of pollen grains deposited by honey bees on stigmas increased gradually after pollen supplementation in the combs. But pollen foraging decreased only moderately, and no effect could be observed on any yield component except the seed set. On the other hand, there was no effect of the pollen paste laid on top of the frames either on stigmatic pollen loads, on colony pollen foraging or on any yield component. Supplementing honey bee colonies with pollen in the combs can therefore be an effective means for increasing their pollinating activity in nectariferous crops displaying anthers isolated from stigmas, e.g., Amaryllidaceae, Apiaceae, Cucurbitaceae, avocado, all hybrid seed productions. The context for the potential use of pollen substitutes is discussed.

The sunflower crop provides an important honey flow for beekeepers. In France, beekeepers observed a decrease in honey yield from this crop these past years compared to the 1980s–1990s. They suspect the new cultivars to be less productive in nectar compared to the older ones, but no data is available to support this, and it is known that climate conditions have a strong impact on nectar secretion. This study aimed to explore the effect of abiotic environmental conditions on nectar secretion in sunflower, as well the range of variation of this secretion in a sample of current cultivars. Thirty-four current sunflower hybrid cultivars were sampled in test plots for their nectar secretion under varying conditions of temperature, air humidity and soil moisture. Air humidity controlled the sugar concentration of nectar, and thus its volume. To study nectar secretion independently from this effect, analyses subsequently focused on nectar sugar mass per floret. The nectar sugar mass increased with temperature up to an optimum of 32 °C, while the variation range of soil water tension was not sufficient to detect an effect on nectar sugar mass. This varied by up to 100% among the 34 cultivars (from 101 to 216 μg sugar per staminate floret in average), with a similar range to those reported in the literature for older cultivars. Likewise, oleic cultivars, a new type introduced since the early 2000s, were found to secrete the same amounts of nectar as linoleic cultivars, an older conventional type. The more self-fertile cultivars also showed no reduction in nectar secretion. Finally, we tested the method that measures the nectar gross secretion rate in one hybrid, and we observed that this hybrid secreted in average 28 μg sugar per hour per staminate floret. The potential benefits of this method were discussed.

Au cours de l'histoire évolutive des plantes à fleurs, l'apparition des nectaires floraux a permis de substituer le pollen par du nectar pour attirer les animaux pollinisateurs, permettant de diminuer les coûts de la pollinisation animale liés à la consommation du pollen. Dans les productions de semence hybride des cultures entomophiles, connaître le niveau de sécrétion nectarifère des lignées en présence, mâle fertile (MF) et mâle stérile (MS), est important si l'on souhaite maximiser les transferts de pollen entre les deux. Dans cet article, nous faisons tout d'abord une revue des méthodes qui existent pour mesurer la sécrétion nectarifère, puis retenons celle qui mesure un taux de sécrétion brut, qui permet d'exprimer une vitesse de sécrétion, pour l'utiliser sur deux lignées de colza d'hiver (Brassica napusL.), la variété hybride F1 Exocet MF et son parent MS. Nous montrons que la sécrétion nectarifère du colza est constante sur un intervalle de temps de 6–8 heures durant les heures du jour, que cette sécrétion admet une température optimale se situant entre 20 °C et 30 °C, et qu'elle est autour de deux fois moindre chez le parent MS par rapport à la lignée F1. Ces résultats permettent de proposer une méthode de mesure rigoureuse pour comparer la sécrétion nectarifère entre lignées ou variétés. Nous concluons sur les principales autres variables dont il faudrait tenir compte pour notamment pouvoir estimer la quantité totale de nectar sécrétée par une surface donnée de culture.