Collaborative Research: the Role of Floral Secondary Compounds in Bee Performance and Disease Transmission in a Natural Ecosystem
Project Number: 1245-21000-277-19
Start Date: Jun 01, 2014
End Date: May 31, 2016
Objective 1. Measure natural variation in the concentration of secondary compounds in nectar and pollen of important agricultural and wild species. The presence of secondary compounds in nectar and pollen has been recognized for decades but only recently have sophisticated chemical approaches examined variation in secondary compound concentration within a species. Cooperators will screen 30 agricultural, horticultural, and native species for the presence, concentration, and identity of secondary compounds in pollen and nectar using GC-MS.
Objective 2. Test the costs and benefits of nectar and pollen secondary compounds on managed bees in the presence and absence of parasites. Parasites have been strongly implicated as one of the major factors driving declines in introduced and native pollinators. Pollinators routinely consume secondary compounds in pollen and nectar that are known to impact predation and parasitism for herbivores. However, the role of such compounds for pollinator performance is largely unknown. ARS will use laboratory experiments focusing on the important managed pollinators, Bombus impatiens and Apis mellifera, and their common parasites, Crithidia bombi and Nosema ceranae. ARS hypotheses are that (a) consumption of secondary chemicals will directly reduce bee performance, measured as survival and reproduction, parallel to secondary compound effects found on herbivores; and that (b) consumption of secondary chemicals will indirectly benefit bees by increasing resistance to parasites, creating a trade-off where floral resources with high secondary compounds benefit parasitized bees but are costly to non-parasitized ones.
Objective 3. Assess how parasites alter bee foraging preferences for secondary compounds. If secondary compounds reduce parasite infection as the pilot data suggest, then parasitism could affect bee foraging choices. ARS will test this hypothesis using laboratory and field preference foraging assays. The hypothesis is that bees will assess their parasite status and prefer diets that are most beneficial dependent on their condition.
For Objective 1, ARS will analyze nectar and pollen of agricultural, native and horticultural species that are commonly visited by bumble and honey bees. Species were selected based on the following criteria: (1) availability as a bee food resource (more abundant or longer-flowering species preferred), (2) presence in the northeastern U.S., to focus project attention on a regional ecosystem (with some crop exceptions, such as almond, citrus and avocado, that will be collected in California), (3) reliance on bee pollinators for reproduction, (4) economic importance (for crops), and (5) prior information about secondary chemicals in floral or leaf tissue. For each species, ARS will collect 5 nectar and 5 pollen samples from separate individuals.
For Objective 2, ARS will manipulate parasitism and secondary compound exposure in factorial experiments in Bombus and Apis using controlled experiments. In the case of honey bee experiments, naïve bees will be fed nectar compounds and then challenged with parasites in sterile cups, leading to mortality measurements and parasite load measurements.
For Objective 3, the Cooperator will assess how parasites alter bee foraging preferences for secondary compounds in the lab and in the field. Methodologies differ for species, but the following points apply to both pollinators. First, preference tests will focus on secondary compounds that affect bee resistance to parasites. The three compounds with strongest effects at reducing pathogen loads and two more that had the least effect will be selected to determine whether the strength of compound effects on pathogens correlates with infected bee preference for those compounds. If all tested compounds reduce infection, five compounds will be chosen that span the range of variation. These will be presented to foraging bees and differential choice experiments will be used to determine pollinator nectar preference.