Butterfly foraging behavior: can butterflies detect nectar in flowering plants?

Abstract

Optimal foraging theory states that there are benefits and costs from foraging. If the animal shows optimal foraging behavior, the benefits minus the costs from foraging should be maximized. One assumption of optimal foraging theory is that animals can recognize food, which for butterflies means detecting nectar in flowering plants. We tested whether butterflies detect nectar in the field when they are foraging, or if they forage randomly until they find rewarding florets. We exposed each Speyeria mormonia male butterfly to a Pyrrocoma crocea flowerhead that was half nectar rich and half nectar poor. We recorded which side of the flowerhead the butterfly probed first and whether or not it continued probing after finding or not finding a reward. The results demonstrated that this species can detect which side of the flowerhead possesses nectar. The estimated number and proportion of nectar rich florets in the nectar rich side did not differ for individuals choosing the nectar-rich or nectar-poor side, which means individuals choosing the nectar-poor side were not doing so because of low nectar content in general. Even though S. mormonia males showed optimal foraging behavior by detecting rewarding florets, they did not use information about rewarding florets in the decision as to whether to keep probing the flower or not. S. mormonia thus lose time and energy probing unrewarding flowers. Further studies with S. mormonia males and females are needed to determine the mechanisms that enable their nectar detecting abilities and whether there are foraging differences related to sex.