The effects of the fungal pathogen, Nosema ceranae, on honey bee (Apis mellifera L.) physiology and behavioral development

Persistent exposure to mite pests, poor nutrition, pesticides, and pathogens threaten the productivity and survival of honey bees in the U.S.  We investigated the effects of infection with an emerging fungal pathogen, Nosema ceranae, on physiological and hormonal factors underlying the division of labor in worker honey bees.  Young bees perform as nurses within the hive and have high levels of the yolk protein, vitellogenin (Vg), and low levels of the endocrine factor, juvenile hormone (JH).  As they transition to foraging behavior, older bees have low levels of Vg and high levels of JH.  The interaction of Vg and JH functions as a pacemaker that drives the sequence of behaviors that workers perform throughout their lives.  We first determined the effects of N. ceranae on foraging onset and life span.  Infected bees were nearly twice as likely to engage in precocious foraging and lived one week less on average compared to uninfected controls.  We next tracked levels of Vg transcript and JH titer in infected bees using cage studies.  Infected nurse-aged bees had significantly lower levels of Vg and higher levels of JH compared to uninfected controls.  These findings support the conclusion that N. ceranae disrupts the expression of traits that honey bees are thought to have co-opted from solitary ancestors to become social.  Further research may provide incite into how specific factors such as infectious diseases affect the ability of honey bee colonies to withstand stress.