Target of rapamycin (TOR) determines appendage size during pupa formation of the red flour beetle Tribolium castaneum.

The adult body size is species-specific and controlled by complex interactions between hormones and the IIS/TOR pathway. To analyze the role of target of rapamycin (TOR) in the growth and development of the insect, expression levels of TOR were silenced in the model and pest insect red flour beetle, Tribolium castaneum. Injection of dsRNA into the last larval instar decreased pupal mass and size, while the amount of food intake by the larvae was not affected. These results place TcTOR downstream of nutrition as a transducer for nutritional signals to increase larval growth. In addition, TcTOR-silencing notably decreased the size of the adult appendages. Analysis of the wings and elytra revealed a decrease in cell size and number of these appendages in the TcTOR-silenced insects. This reduction in size was correlated with a decrease of transcriptional levels of marker genes controlling the cell cycle. Altogether, these results suggest a pivotal role for TcTOR in integrating nutritional signals and regulation of body and appendages growth.