Effects of nectar contents on the foraging activity of honeybee (Apis mellifera) on Asian pear (Pyrus pyrifolia Nakai)

The foraging preferences of Apis mellifera for flower depend on the content of sugar and amino acid in nectar. To determine the factor in nectar that attracts honeybee in field, we investigated the foraging rate of honeybee, fruit set, relationship between the foraging behavior of honeybee and contents of nectar in different Asian pear cultivars (‘Niitaka’ and ‘Whangkeumbae’), which do not produce pollen. The foraging rate of honeybee on ‘Whangkeumbae’ was 2 times higher than that on ‘Niitaka’ and the fruit set of ‘Whangkeumbae’ was 1.5 times higher than that of ‘Niitaka’. ‘Whangkeumbae’ exhibited 3.7 times higher nectar secretion than ‘Niitaka’. The total sugar content in the nectar of ‘Whangkeumbae’ was 1.1–1.7 times higher than that in the nectar of ‘Niitaka’, and this difference was significant. Furthermore, the content of glucose, fructose, and sucrose in the nectar of ‘Whangkeumbae’ was higher than that in the nectar of ‘Niitaka’. In particular, the content of sucrose in ‘Whangkeumbae’ was 1.3–3.2 times higher than that in ‘Niitaka’; sucrose is known to be the most preferred sugar by honeybee. Among the 20 amino acids detected in both cultivars, the content of Nine amino acids was significantly different. The content of phenylalanine and glycine (which are preferred by honeybee) in ‘Whangkeumbae’ was 1.4–2.4 times higher than that in ‘Niitaka’. In contrast, the content of asparagine (which is not preferred by honeybee) in ‘Niitaka’ was 1.1–2.4 times higher than that in ‘Whangkeumbae’. Among the sugars in nectar, sucrose exhibited the highest relationship with the number of foraging bees, followed by glucose and fructose. Among the amino acids, phenylalanine presented the highest correlation with the number of foraging bees, followed by glycine and alanine. The results suggest that honeybees prefer ‘Whangkeumbae’ over ‘Niitaka’ because of the difference in the amino acid and sugar content in the nectar of pear cultivars.