These proteins are involved in sterol homeostasis. Among these C. populi ABCG sequences, Cpabc55 showed the most elevated transcript level. Its deduced protein is homologous to TcABCG4C whose involvement in the transport of lipids to the cuticle has been suggested and, thus, that it is required for the formation of a waterproof barrier in the epicuticle. Cpabc55 is also highly Mesatlantin C expressed in glands and fat body tissue but not in the Malpighian tubules. The expression of Tcabcg-4c was higher in intestinal/excretory tissues than in carcass tissue. The function of the other four ABCG transporters cannot be predicted from our analyses. However, it has been demonstrated recently that an ABCG1-homolog in the fungus Grossmannis clavigera confers tolerance to monoterpenes which contributes to the fungus’ ability to cope with the chemical defence of its host plant. Therefore, the ABCG proteins’ specificity in insects may not be limited to sterols or lipids but may have a broader substrate spectrum – that is not known to date. Insect Malpighian tubules are critical for osmoregulation. Moreover, the tubules have the capability to excrete actively a broad range of organic solutes and xenobiotics,Pulchinenoside A such as insecticides. Recently, we have shown a role of the excretion system in the homeostasis of phytochemicals in the larval body of leaf beetles. Additionally, the tubules play a significant role in immunity by sensing bacterial infections and mounting an effective killing response by secretion of antimicrobial peptides. We found 21 transcripts abundant in the Malpighian tubules of C. populi encoding members of the following subfamilies known to contain multidrug resistance proteins: four of ABCB, 14 of ABCC, three of ABCG. Among the four predicted ABCB members displaying a high mRNA level in the Malpighian tubules, two, CpABC7 and 12, were already described in the gut section above. The third candidate, CpABC8, is most similar to human mitochondrial ABCB10. For ABCB10 different roles have been suggested, including protection against toxic reactive oxygen species, heme synthesis, or peptide transport. For this tissue, we speculate that it is involved in antimicrobial peptide transfer.