The forth ABCB protein, CpABC9, clusters together with the human mitochondrial ABCB7 which is involved in the ironsulfur cluster assembly essential for multiple metabolic pathways throughout the cell. RNAi of the homologous TcABCB-5A demonstrated the pivotal function of this gene in the red flour beetle: its down-regulation resulted in severe morphological defects and Salidroside high mortality depending on the developmental stage treated. Hence, the three most likely mitochondrial localized ABCB candidates, namely CpABC7-9, are proposed to be of vital importance in the cells. However, for CpABC12, which is a full transporter and clusters to human proteins related to xenobiotic resistance, we can predict a similar function in the larval excretion system. Most putative ABC transporter transcripts identified in C. populi are present at a high level in the excretion system of the juvenile beetles compared to the other tissues. Particularly, the 14 candidates belonging to the ABCC subfamily are the most highly transcribed compared to other subfamilies in this tissue. Remarkably, one of the highly expressed candidates, CpABC16, clusters in our phylogeny together with CpABC35 which is involved in the accumulation of Liquiritin plant-derived metabolites. Therefore, it is tempting to speculate a role for CpABC16 in the excretion of phytochemicals in C. populi larvae. Among the three candidates of the G-subfamily, two are highly transcribed only in the Malpighian tubules: CpABC54 is a homolog of TcABCG-9B from the White group and CpABC62 is homologous to TcABCG-9A from the Scarlet group. RNAi targeting Tcabcg-9a or b resulted in both cases not only in white eyes but also in a whitish appearance of the Malpighian tubules due to the absence of tryptophan metabolites/kynurenine and pteridines. These eye pigment precursors are stored and processed in the larval tubules before being released for further conversion into pigments in the developing adult eyes. In addition, in D. melanogaster White is expressed in intracellular vesicles in tubule principal cells, suggesting that White participates in vesicular transepithelial transport of cGMP. CpABC57 is the only ABCG candidate that is also expressed in the intestine and belongs to the human ABCG1 and ABCG4 branch.