Contributions to the ecology of North American vespines: Rearing yellowjackets in nest boxes and unraveling pheromone-mediated nest defense in bald-faced hornets

To obtain an ample supply of study insects, we attempted to rear yellowjackets from spring-collected queens, achieving a high nest initiation rate for German yellowjackets, Vespula germanica. To study nest defense, we placed paired boxes near the nest entrance of bald-faced hornets, Dolichovespula maculata, and audio recorded sound impulses caused by nest mates striking the boxes. The number of strikes increased 27-fold when – compared to two control boxes – one of the two boxes was treated with venom sac extract (VSE), providing evidence for an alarm response. The VSE-treated box also induced a greater proportion of strikes than the corresponding control box, providing evidence for a target-oriented response. Analyzing VSEs by gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry, we identified seven candidate pheromone components which – based on molecular structure – triggered primarily alarm or target-oriented responses. VSE was more effective than synthetic pheromone in triggering alarm, indicating a missing alarm pheromone component.