Far-ranging pollinators follow floral scent trails to their host plants, but under polluted conditions, primary floral volatiles (PFVs)are oxidized, and novel secondary floral volatiles (SFVs) result. Insects’ abilities to associate these new scents with floral rewards while on the wing could be crucial to their foraging efficiency. In this study, we use three methods to assess the ability of naive bumblebees Bombus impatiens’ (B. impatiens) to associatively learn a PVF (linalool) and two resulting SFVs (acetone and formaldehyde) to determine if bees can learn SFV’s as well or as quickly as PFV’s. The three methods—proboscis extension reflex (PER), free-flying foraging in a 12X5' tent, and y-tube choice tests—enabled us to cross reference results, and offered insights into the relationship between the commonly used Pavlovian PER response and actual behavioral response of B. impatiens. The experimental design for the methods tested speed and accuracy of independent scent learning, with B. impatiens choosing between a rewarded scented option, and an unrewarded, unscented options. For both in-tent and y-tube choice tests, bees were “trained” by being exposed to a scented and rewarded artificial flower: for PER, reward was deliver in the traditional method via a syringe without other stimulus present.
For all three methods, B. impatiens learned linalool more quickly than acetone and formaldehyde. For in-tent foraging and PER tests, bees also demonstrated a better associative learning for linalool than acetone. Free flying bees in tents made almost 30% fewer errors after demonstrating learning (after 80% of foraging visits were on scented flowers) when linalool was the reward-associated scent vs. when acetone was the reward-associated scent. For PER tests, after once extending its proboscis in response to a scent, B. impatiens made 25% fewer errors in the next 10 trails when linalool was the scent vs. when acetone was the scent. B. impatiens learned all three scents more quickly and made the fewest errors with the PER training, indicating that PER may overestimate the ability of bees to learn and respond to new scents. B. impatiens’ higher learning capacity for a primary floral volatile, and difficulty learning scents in free flight studies indicates that learning new, oxidized products of PFV’s may pose a serious obstacle to pollinators, effecting their foraging efficiency.