Abstract
Foraging animals must often decide among resources which vary in quality and quantity. Nectar is a resource that exists along a continuum of quality in terms of sugar concentration and is the primary energy source for bees. Alternative sugar sources exist, including fruit juice, which generally has lower energetic value than nectar. We observed many honeybees (Apis mellifera scutellata) foraging on juice from fallen guava (Psidium guajava) fruit near others foraging on nectar. To investigate whether fruit and nectar offered contrasting benefits of quality and quantity, we compared honeybee foraging performance on P. guajava fruit versus two wildflowers growing within 50 m, Richardia brasiliensis and Tridax procumbens. Bees gained weight significantly faster on fruit, 2.72 mg/min, than on either flower (0.17 and 0.12 mg/min, respectively). However, the crop sugar concentration of fruit foragers was significantly lower than for either flower (12.4% vs. 37.0% and 22.7%, respectively). Fruit foragers also spent the most time handling and the least time flying, suggesting that fruit juice was energetically inexpensive to collect. We interpret honeybee foraging decisions in the context of existing foraging models and consider how nest‐patch distance may be a key factor for central place foragers choosing between resources of contrasting quality and quantity. We also discuss how dilute solutions, such as fruit juice, can help maintain colony sugar–water balance. These results show the benefits of feeding on resources with contrasting quality and quantity and that even low‐quality resources have value.
Highlights
Foraging decisions are often based on increasing the rate or efficiency of food collection (Cowlishaw, 1997; Houston & McNamara, 2014; Scrimgeour & Culp, 1994; Waite & Ydenberg, 1994; Wang, Ings, Proulx, & Chittka, 2013)
Apis mellifera scutellata, foraging on three sugar resources: fruit fallen from guava trees, Psidium guajava (Myrtaceae), and two species of wild flowers, Tridax procumbens (Asteraceae) and Richardia brasiliensis (Rubiaceae), growing in patches in lawns (Figure 1)
We tested for the effect of foraging resource (P. guajava, R. brasiliensis, and T. procumbens) on four measures of honeybee foraging performance: rate of weight change, crop sugar concentration, visitation rate and proportion of time spent handling
Summary
Foraging decisions are often based on increasing the rate or efficiency of food collection (Cowlishaw, 1997; Houston & McNamara, 2014; Scrimgeour & Culp, 1994; Waite & Ydenberg, 1994; Wang, Ings, Proulx, & Chittka, 2013). Nectar contains other nutrients such as amino acids, but these are normally present in small amounts which are of secondary importance for bees assessing flower quality (Hendriksma, Oxman, & Shafir, 2014) Both volume and sugar content of nectar vary greatly among species and with environmental conditions, giving bees many choices (Corbet, Unwin, & Prŷs- Jones, 1979; Heil, 2011). Honeybees can fly considerable distances to food sources (Beekman & Ratnieks, 2000; Couvillon, Schürch, & Ratnieks, 2014; Ratnieks & Shackleton, 2015), and colonies show great ability to direct their forager workforce to the most rewarding sources (Seeley, Camazine, & Sneyd, 1991) Why, do they gather dilute fruit juice when nectar is available? To test whether resources had contrasting benefits of quality and quantity, we compared the foraging performance of honeybees on fallen P. guajava fruits versus two species of wild flowers growing nearby. We quantified the activity patterns of bees on each resource, to test the prediction that fruit foragers spend more time handling and less time on the energetically expensive activity of flying between food items
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