Chemical ecology of Bombus pauloensis: first evidence of an alarm pheromone?

FLORENCIA PALOTTINI; ALEJANDRO LUCÍA; MARÍA SOL BALBUENA

Congreso; Bombus 3.0; 2023

Eusocial insects represent complex societies where task coordination requires information transmission and high levels of communication among colony members. Such communication is mainly based on pheromones that mediate and/or determine reproductive status, resource gathering and nest defense. The existence of alarm pheromones (AP) and the defense mode to danger is of utmost relevance for the survival of the colony as a whole. Unlike honey and stingless bees, it is not well known whether bumblebees emit an AP. However, working with disturbed workers of Bombus pauloensis, a South American species, we have noticed an awful and strong smell (to the human perception) released jointly with a clear defense behavior whereby individuals sting and bite, causing attack and attraction of nest mates. The aim of the present work was to describe the chemical compounds and to study the antennae detection of the odor released in an alarm context. First, we performed several dissections to define the emission source. Also, we carried out volatiles collections using Solid phase micro-extraction technique and identified, by means of Gas chromatography coupled to mass spectrometry, the chemical compounds involved. Finally, we conducted electrophysiological assays to evaluate the antennae responses. Our results showed that the smell is released from the mandibles of disturbed bumblebee workers and is composed of 14 volatiles with 2-heptanone, butyric acid and rose oxide as the major compounds of the blend. Besides, we found that antennae showed significantly higher responses to odors coming from disturbed individuals than to those coming from undisturbed ones, without responses to the sting gland odor. We also measured the electroantennographic records to different concentrations of the main compounds of the mandibular blend. Herein we provide the first report about a particular repulsive blend released by disturbed bumblebees, suggesting the presence of an AP. Future behavioral experiments are necessary to define its biological function.