Understanding the effect of pesticides on the survival of honeybee colonies is 
important because these pollinators are reportedly declining globally. In the 
present study, we examined the changes in the head proteome of nurse honeybees 
exposed to individual and combined pesticides (the fungicide pyraclostrobin and 
the insecticide fipronil) at field-relevant doses (850 and 2.5 ppb, 
respectively). The head proteomes of bees exposed to pesticides were compared 
with those of bees that were not exposed, and proteins with differences in 
expression were identified by mass spectrometry. The exposure of nurse bees to 
pesticides reduced the expression of four of the major royal jelly proteins 
(MRJP1, MRJP2, MRJP4, and MRJP5) and also several proteins associated with 
carbohydrate metabolism and energy synthesis, the antioxidant system, 
detoxification, biosynthesis, amino acid metabolism, transcription and 
translation, protein folding and binding, olfaction, and learning and memory. 
Overall, when pyraclostrobin and fipronil were combined, the changes in protein 
expression were exacerbated. Our results demonstrate that vital proteins and 
metabolic processes are impaired in nurse honeybees exposed to pesticides in 
doses close to those experienced by these insects in the field, increasing their 
susceptibility to stressors and affecting the nutrition and maintenance of both 
managed and natural colonies.