Reversal learning and risk-averse foraging behavior in the Monarch Butterfly, Danaus plexippus (Lepidoptera: Nymphalidae)

Background/Question/Methods Learning ability allows insects to respond to a variable environment, and to adjust their behaviors in response to positive or negative experiences. Pollinating insects readily learn to associate floral characteristics, such as color, shape, or pattern, with appetitive stimuli, such as the presence of a nectar reward. However, in nature pollinators may also encounter flowers that contain distasteful or toxic nectar, or offer highly variable nectar volumes, providing opportunities for aversive conditioning or risk-averse foraging behavior.  Whereas some bees learn to avoid flowers with unpalatable or unreliable nectar rewards, little is known about how Lepidoptera respond to such stimuli. 

Results/Conclusions We used a reversal learning paradigm to establish that monarch butterflies learn to discriminate against colored artificial flowers that contain salt solution, decreasing both number and duration of probes to flowers of a preferred color and altogether avoiding those of a non-preferred color.  In addition, when we offered butterflies artificial flowers of two different colors, both of which contained the same mean nectar volume but which differed in variance (flowers of one color all contained 2 ul of sucrose solution; flowers of the other color contained 4 ul sucrose or none at all), the monarchs exhibited risk-averse foraging: they probed the constant flowers significantly more than the variable ones, regardless of flower color. Our results demonstrate that monarchs can respond to aversive as well as appetitive stimuli, and can also adjust their foraging behavior to avoid floral resources with high variance rewards.