RESEARCH PAPER Reversal Learning and Risk-Averse Foraging Behavior in the Monarch Butterfly, Danaus plexippus (Lepidoptera: Nymphalidae) Daniela Rodrigues*, Brad W. Goodner & Martha R. Weiss* * Department of Biology, Georgetown University, Washington, DC, USA  Department of Biology, Hiram College, Hiram, OH, USA Introduction Learning allows insects to respond to variable or unpredictable environments (Stephens 1993; reviewed in Dukas 2008). Many studies have dem- onstrated that bees, wasps, flies, butterflies, and grasshoppers, among other insects, can develop a positive association between visual and ⁄ or olfactory cues and resources such as nectar or oviposition sites (e.g., Shafir 1996; Dukas 1999; Dukas & Bernays 2000; Weiss & Papaj 2003; Cnaani et al. 2005). Addi- tionally, insects in a range of taxa can learn to associate visual and olfactory cues with negative or aversive stimuli such as salt, shock, toxins, poor quality food or distractors (e.g., Berenbaum & Mili- czky 1984; Tully & Quinn 1985; Lee & Bernays 1990; Bernays 1993; Bowdish & Bultman 1993; Dukas & Bernays 2000; Matsumoto & Mizunami 2002; Chittka et al. 2003; Dyer & Chittka 2004; Davis 2005; Vergoz et al. 2007; Blackiston et al. 2008). Learning to associate biologically relevant cues with either positive or negative stimuli can increase an insect’s fitness (e.g., Dukas & Bernays 2000). Correspondence Daniela Rodrigues, Departamento de Biologia Animal, IB, UNICAMP, Campinas, SP, Brazil. E-mail: dani_rodrig@yahoo.com.br Received: September 22, 2009 Initial acceptance: November 16, 2009 Final acceptance: December 12, 2009 (D. Zeh) doi: 10.1111/j.1439-0310.2009.01737.x Abstract Learning ability allows insects to respond to a variable environment, and to adjust their behaviors in response to positive or negative experi- ences. 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 learning 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. 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 of probes and probing time on flowers of a preferred color and altogether avoiding artificial flowers 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, the monarchs exhibited risk-averse foraging: they probed the constant flowers significantly more than the variable ones, regardless of flower color or butterfly sex. Our results add to our understanding of butterfly foraging behavior, as they 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. Ethology 270 Ethology 116 (2010) 270–280 ª 2010 Blackwell Verlag GmbH ethology international journal of behavioural biology