Honest signaling? Testing the toxic pheromone hypothesis in the highly social bees, Lestrimelitta niitkib and Apis mellifera
Species in the stingless bee genus, Lestrimelitta, like L. niitkib, are all obligate cleptoparasites. Rather than foraging for resources, these bees rob the hives of other social bees, native and introduced. Multiple hypotheses have been proposed as to why L. niiitkib and other Lestrimelitta species are so successful at robbing. In all hypotheses, the copious release of mandibular gland pheromone (MGP) during robbing plays a key role. We propose a new hypothesis, that MGP is a toxin that also honestly signals the greater physical fighting ability of L. niitkib. To test this hypothesis we examined the fighting ability and mandible morphology of L. niitkib. We also injected natural and synthetic MGP into victims. In both fighting and injection trials, victims increased their rate of falling, abnormal movement, and time spent motionless. Given that Lestrimelitta can repeatedly raid the same colonies, victims should be able to learn to associate MGP with attacks. We therefore propose that multiple MGP hypotheses can be considered under the umbrella of honest signaling, in which the honestly superior attack ability of L. niitkib is associated with MGP. In addition, we also have conducted preliminary experiments examining whether honey bee mandibular gland secretions (MGS) are an alarm pheromone. We hypothesize that marking predatory targets at the entrance of the hive with MGS should elicit more attention if MGS is indeed an alarm pheromone. We also tested the toxicity of MGS and found weak support for the hypothesis that it is toxic.