Beyond the physiological and behavioural differences in appendage morphology Itraconazole (Sporanox) between the workers and queens of are pre-eminent. unknown. Leg phenotype determination takes place between the fourth and fifth larval instar and herein we show that the morphogenesis is completed at brown-eyed pupa. Using results from the hybridization of whole genome-based oligonucleotide arrays with RNA samples from hind leg imaginal discs of pre-pupal honeybees of both castes we present a list of 200 differentially expressed genes. Notably there are castes preferentially expressed cuticular protein genes and members of the P450 family. We also provide results of qPCR analyses determining the developmental transcription profiles of eight selected genes including and (expression in workers hind leg is approximately 25 times higher than in queens. Finally immunohistochemistry assays show that Ubx localization during hind leg development resembles the bristles localization in the tibia/basitarsus Itraconazole (Sporanox) of the adult legs in both castes. Our data strongly indicate that the development of the hind legs diphenism characteristic of this corbiculate species is driven by Itraconazole (Sporanox) a set of caste-preferentially expressed genes such as those encoding cuticular protein genes P450 and Hox proteins in response to the naturally different diets offered to honeybees during the larval period. Introduction queens and workers are prime examples of how deeply the environment can affect ontogenesis. These two classes of females named castes develop from genetically equivalent eggs that undergo different developmental pathways in response to different diets thus constituting an example of the widespread phenomenon of developmental plasticity. Processes and concepts associated with this phenomenon have attracted researchers’ attention over time. Despite this interest the genetic cascade linking nutrition to the morphological outputs in such divergent and specialized organisms is unknown and represents a very interesting biological problem. The development of complex traits such as wings and other appendages is strongly influenced by nutrition and population conditions . In bees a differential protein-containing diet is responsible for the high levels of juvenile hormone (JH) observed in queens which in turn directs larval development and the morphological differences observed in both castes . JH has been described as one of the major components of insect development integrating reproduction and the development of morphological traits. However in the honeybee ((((((((in developing honeybee hind legs is negatively correlated with bristle distribution in the corbicula. These results indicate that a differential nutrition during the initial stages of post-embryonic development leads to the establishment of differential gene expression patterns including the caste-specific transcription and translation of a Hox gene which seems to be FTSJ2 a key player during the differential development of hind legs in honeybee castes. Results Morphological Analyses The differences in hind leg morphology between castes of adult honeybees meaning bristle patterning  and the stage in which the developmental determination of these caste-specific structures takes place are widely known  . To determine the stage the bristles are formed we dissected hind legs from worker and queen pupae for Scanning Electron Microscopy (SEM) analyses. We found that all bristles are formed and correctly positioned in worker and queen hind legs in brown-eyed pupae (Pb) just after apolysis (Fig. 1A and Fig. 1D). Interestingly we found that the cuticle of worker hind legs is formed by polygonal scales which contrasts with the smooth appearance of the same region in queens (compare Fig. 1B and 1E arrowhead). In addition bristles of the tibia in worker hind legs have a characteristic socket usually observed in mechanoreceptors (external proprioceptors). These bristles differ strikingly with the bristles found on queen legs which do not contain this socket aspect  (Fig. 1B and 1E arrow; Fig. 1C and 1F detail). Figure 1 SEM images showing divergent morphologies of worker and queen hind legs during pupal development (Pb). Microarray Analyses We performed oligonucleotide microarray hybridization analyses.