Abstract
Foraging behavior is a critical adaptation by insects to obtain appropriate nutrients from the environment for development and fitness. Bumble bees (Bombus spp.) form annual colonies which must rapidly increase their worker populations to support rearing reproductive individuals before the end of the season. Therefore, colony growth and reproduction should be dependent on the quality and quantity of pollen resources in the surrounding landscape. Our previous research found that B. impatiens foraging preferences to different plant species were shaped by pollen protein:lipid nutritional ratios (P:L), with foragers preferring pollen species with a ~5:1 P:L ratio. In this study, we placed B. impatiens colonies in three different habitats (forest, forest edge, and valley) to determine whether pollen nutritional quality collected by the colonies differed between areas that may differ in resource abundance and diversity. We found that habitat did not influence the collected pollen nutritional quality, with colonies in all three habitats collecting pollen averaging a 4:1 P:L ratio. Furthermore, there was no difference in the nutritional quality of the pollen collected by colonies that successfully reared reproductives and those that did not. We found however, that “nutritional intake,” calculated as the colony‐level intake rate of nutrient quantities (protein, lipid, and sugar), was strongly related to colony growth and reproductive output. Therefore, we conclude that B. impatiens colony performance is a function of the abundance of nutritionally appropriate floral resources in the surrounding landscape. Because we did not comprehensively evaluate the nutrition provided by the plant communities in each habitat, it remains to be determined how B. impatiens polylectic foraging strategies helps them select among the available pollen nutritional landscape in a variety of plant communities to obtain a balance of key macronutrients.
Highlights
An appropriate quality and quantity of macronutrients are essential for development and reproduction of every organism (Behmer, 2009; Behmer & Joern, 2008)
Mounting evidence suggests that bumble bees (Hymenoptera: Apidae: Bombus spp.), especially B. impatiens and B. terrestris, show foraging preferences for plant species based on nutritional quality of pollen (Cardoza, Harris, & Grozinger, 2012; Hanley, Franco, Pichon, Darvill, & Goulson, 2008; Kitaoka & Nieh, 2008; Kriesell, Hilpert, & Leonhardt, 2016; Leonhardt & Blüthgen, 2011; Ruedenauer, Spaethe, & Leonhardt, 2016)
To determine whether the metrics of pollen nutritional quality were correlated to metrics of colony growth and reproduction, independent of habitat, we conducted a principal components analysis (PCA) with the following variables related to (1) pollen nutrition: colony average pollen protein, lipid, and sugar concentrations and P:L values; (2) foraging behavior and resource availability: colony average “pollen foraging rate” and “nonpollen foraging rate” and colony average pollen load mass collected per forager; (3) colony growth: lifetime population, maximum biomass, maximum biomass gain; and (4) reproduction: reproductive success and total number of reproductive individuals produced
Summary
An appropriate quality and quantity of macronutrients are essential for development and reproduction of every organism (Behmer, 2009; Behmer & Joern, 2008). Mounting evidence suggests that bumble bees (Hymenoptera: Apidae: Bombus spp.), especially B. impatiens and B. terrestris, show foraging preferences for plant species based on nutritional quality of pollen (Cardoza, Harris, & Grozinger, 2012; Hanley, Franco, Pichon, Darvill, & Goulson, 2008; Kitaoka & Nieh, 2008; Kriesell, Hilpert, & Leonhardt, 2016; Leonhardt & Blüthgen, 2011; Ruedenauer, Spaethe, & Leonhardt, 2016) This preference aligns with a goal of providing optimal resources for their brood, because suboptimal pollen quality can lead to reproductive deficit, egg cannibalism, and larval ejection (Génissel, Aupinel, Bressac, Tasei, & Chevrier, 2002; Tasei & Aupinel, 2008). These data provide critical information integrating nutritional intake of bumble bees with colony behavioral dynamics, growth, and fitness
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