Fighting Infection the Apine Way

Common Carder Bee, Bombus pascuorum

This is the time of the year for getting sick. That's not a statistic, its just personal experience. The cold and dark days mean we spend more time cooped up in close proximity to others: others who are sick. And so it spreads to us, whatever it may be, laying us low till our immune systems kick in and get us back on the road. Yet if being close to other, infected individuals is a risk of disease, it must be hell for bees. Take the Common Carder Bee, Bombus pascuorum. A eusocial bee, it nests on the ground in colonies of up to 200 individuals (1). Break out the cough syrup, bee sized spoons.
 

Common Carder Bee, Bombus pascuorum

However, B. pascuorum has a sophisticated defence system for dealing with infection. A tough, outer cuticle must first be breached by invaders (2). If they are successful in getting past this first line of defence, a complex interaction of innate humoral and cellular immune reactions are activated in both the bee's tissues and haemocoel (2). Probably the best characterised of these responses is the synthesis of antimicrobial peptides. B. pascuorum produces a defensin, an apidaecin, an abaecin and an N-terminally blocked molecule which provides the bee with antimicrobial activity against fungi, Gram-positive and Gram-negative bacteria (2).
 

Common Carder Bee, Bombus pascuorum

Such a sophisticated defence system does have its drawbacks. Parasitism of B. pascuorum by species of Conopid fly is common (3), but often the hosts show no obvious effect due to the action of the defensive system. Activation of this system is quite energy expensive and under limiting food conditions (which is increasingly becoming the norm for bee populations in Ireland and Europe as a whole(4)) leads to significant decrease in survival (5).

References:

1. Chinery, 2004. Collins Gem Insects p. 251
2. Rees et al., 1997. Insect Biochemistry and Molecular Biology 27 pp. 413-422
3. Moret et al., 2000. Science 290 p 1166-1167
4. Brown and Paxton, 2009.  Apidologie 40 pp. 410-416
5. Moore, 2002. Parasites and the Behaviour of Animals p. 209