Enhancing Alfalfa (Medicago sativa) Seed Yield: The Effect of Honey Bee (Apis mellifera) Supplementation and Efficiency of Other Pollinators

Abstract

Alfalfa (Medicago sativa) is an important fodder crop with 16-25% protein and 20-30% fibre content. It requires pollinators for seed development through a process known as "tripping". Honey bees are preferred for their easy management and mass rearing to enhance pollination. In a field experiment, we tested three treatments: two honey bee colonies (moderately supplemented), three honey bee colonies (highly supplemented), and a control with no honey bee colonies. The colonies European honey bee, A. mellifera, were used, starting at the flowering stage. We assessed the abundance, foraging, and tripping behaviour of pollinators, as well as the number of seeds per pod, pod weight, and seed weight. Honey bees were the most abundant in supplemented plots, followed by solitary bees, with increased honey bee visitation in the second year. Megachile cephalotes, M. hera, and A. mellifera were the most efficient pollinators regarding seeds per pod and seed weight. The plot with two honey bee colonies had a higher seed yield than the one with three colonies. Conservation of these pollinators and the introduction of managed A. mellifera colonies can lead to sustainable alfalfa seed production. Our findings suggest that honey bee supplementation, along with conservation efforts for solitary bees, can enhance pollination and seed yield in alfalfa.

Keywords: bees; fodder; foraging behaviour; tripping behaviour.

Figure 1

Experimental layout showing three pollination treatments in alfalfa fields: (A) Non-supplemented plot with no honey bee colonies, (B) Moderately supplemented plot with two Apis mellifera colonies placed at the field edges, and (C) Highly supplemented plot with a three A. mellifera colonies surrounding the field. The illustration represents the relative abundance of honey bees and colony placement across the treatments to assess the impact of honey bee supplementation on pollinator activity and seed set.

Figure 2

Abundance of different pollinator species visiting lucerne flowers in 2022: (A) non-supplemented block, (B) moderately supplemented block, and (C) highly supplemented block. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05). Pollinator group abbreviations: AMEL—Apis mellifera, OBEE—other honey bees; SFLY—syrphid flies; SBEE—solitary bees; BTFS—butterflies; WASP—wasps.

Figure 3

Abundance of different pollinator species visiting lucerne flowers in 2023: (A) non-supplemented block, (B) moderately supplemented block, and (C) highly supplemented block. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05). Pollinator group abbreviations: AMEL—Apis mellifera, OBEE—other honey bees; SFLY—syrphid flies; SBEE—solitary bees; BTFS—butterflies; WASP—wasps.

Figure 4

Stay time (time spent per flower) of different pollinator species in two years, (A) 2022 and (B) 2023. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05).

Figure 5

Visitation rate (number of flowers visited per minute) of different pollinator species in two years, (A) 2022 and (B) 2023. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05).

Figure 6

Tripping trends in alfalfa flowers (tripped vs. already-tripped flowers) by different pollinator species in (A) 2022 and (B) 2023. Error bars indicate standard error.

Figure 7

Seed weight (grams) per square meter in different supplementary pollination treatments in (A) 2022 and (B) 2023. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05).

Figure 8

Yield parameters after a single visit by different pollinator species in a lucerne crop: (A) pod weight in grams, (B) seed weight in grams, and (C) seed number per pod. Standard error bars with the same letters are not significantly different (Tukey–Kramer test, α  =  0.05).