The 11th Century French chronicler Rodolfus Glaber has an...interesting story about a French peasant called Leutard who is stung by bees. In Leutard's curious tale, the bees sting him in a dream, and order him to do "things impossible to humankind". In response, he smashes up his local church and starts preaching, during which he urges people not to pay their tithes. When the local clergy return the people to the fold, a dejected Leutard hurls himself down a well. This may be the only instance I can come across in which bees, metaphysical or otherwise, are responsible for somebody's death. By combing through centuries of parish rolls, we might find the recorded death of others who fell victim to stings or bites.

Æthelwulf dying of an allergic reaction wouldn't be impossible at all during the 9th Century. English medical texts like Bald's Leechbook, however, while accutely aware of how to effective deal with gangrene, treat infections or aid an inflamed liver, are quite unaware of how to deal with allergies, or indeed even what allergies are. For what it's worth, the actual cause of Æthelwulf's death is completely unrecorded in any contemporary literature. It could have been a bee sting, but it could equally have been from falling out of bed or The Salmon Mousse. The Anglo-Saxon Chronicle as a rule tends to record the causes of unusual or premature death of monarchs, and seeing as no mention is made in the case of Alfred's father, it's far more likely he died of old age, or affiliated similar natural causes.