Insect cuticle is a first physical barrier to protect their body from multifarious environments. Cuticle tanning (sclerotization and pigmentation) is a complex process involves hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA), decarboxylation of DOPA to dopamine, N-acylation of dopamine to N-acetyldopamine (NADA) or N-β-alanyldopamine (NBAD), oxidation of NADA and NBAD to their corresponding quinones, and reactions between the quinones or quinone derivatives with cuticular proteins (CPs) resulting in protein cross-linking. N-acetyltransferase (NAT) catalyzes the conversion of dopamine to NADA whose covalent-linkage of CPs is correlated with colorless cuticle (β-sclerotization). In this study, we analyzed functions of TcNAT1 on cuticle tanning of adult Tribolium castaneum by RNAi. Injection of dsRNA for TcNAT1 (dsTcNAT1) had no affect on animal development and growth. However, some of the resulting adults (~70%) showed split elytra that could not cover their abdomen, resulting in improper folding of their hindwings. Interestingly, body color of the mature adults was darker than that of control dsTcVer-treated adults because probably due to the buildup of abnormally high levels of dopamine, which is used for dopamine eumelanin pigment synthesis (black pigment). On elytra and hindwings of these adults, darker pigments were observed around the sensory bristles located at the intervein regions, suggesting that NADA mediated β-sclerotization is occurred in these regions. Similarly, darker pigment was evident at veins of the hindwings of TcNAT1-deficient adults. These results suggest that TcNAT1 plays important roles in cuticle tanning of T. castaneum adult. To characterize enzymatic properties of TcNAT1, furthermore, recombinant TcNAT1 protein expressed in E. coli was purified by utilizing Ni-NTA affinity column chromatography. This work was supported by NRF (NRF-2012R1A2A1A01006467).

Insect cuticle/exoskeleton is a first physical barrier to protect their body from multifarious environments such as desiccation, natural enemies and entomopathogenic microorganisms. Cuticle tanning (sclerotization and pigmentation) is a vital procedure for generating suitable cuticle depending on body region by sclerotization and pigmentation in insects. Insect cuticle tanning is a complex process involves hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA), decarboxylation of DOPA to dopamine, N-acylation of dopamine to N-acetyldopamine (NADA) or N-β-alanyldopamine (NBAD), oxidation of NADA and NBAD to their corresponding quinones, and reactions between the quinones or quinone derivatives with cuticle protein (CP) side chains resulting in protein cross-linking. One type of pigmentation (quinone tanning) is associated with the covalent linkage of CPs to the ring component of NBAD. In contrast, linkage of CPs to the side chain of NADA (b-sclerotization) is correlated with colorless cuticle. N-acetyltransferase (NAT) catalyzes the conversion of dopamine to N-acetyl dopamine (NADA) in cuticle tanning pathway. In this study, we studied function of TcNAT1 on adult cuticle tanning by double stranded-RNA (dsRNA) mediated gene silencing. Injection of dsTcNAT1 had no affect on animal development, growth and molting such as larva to larva, larva to pupa and pupa to adult. However, some of the resulting adults (~70%) showed split elytra that could not cover their abdomen, resulting in improper folding of their hindwings. Interestingly, body color of the mature adults (older than 3 days) was darker than that of control dsTcVer treated adults because probably due to the buildup of abnormally high levels of dopamine, which is used for dopamine eumelanin pigment synthesis (black pigment) and dopamine quinone-mediated protein crosslinking. On elytra and hindwings of these adults, darker pigments were observed around the sensory bristles that are located in the intervein regions, suggesting that NADA mediated b-sclerotization is occurred at these regions. Similarly, darker pigment was evident at veins of the hindwings of the dsTcNAT1-mature adults. These results suggest that TcNAT1 have important roles in sclerotization and pigmentation of adult body and wings (elytron and hindwing). This work was supported by NRF (NRF-2012R1A2A1A01006467).

This study investigated the antioxidant effect of Hermetia illucens larvae using different extraction temperatures and solvents. We found significant differences in total phenolic content (TPC), total flavonoid content (TFC), an in three antioxidant indexes 2,2-diphenyl-1-picrylhydrazyl (DPPH), 1,1’-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), and ferric-reducing antioxidant power (FRAP) contents, among the samples depending on the extraction temperature and solvent used. The sample extracted with water at 45℃ (HIW-45℃) showed the highest TPC, DPPH, ABTS, and FRAP contents, while the sample extracted with water at 90℃ (HIW-90℃) showed the highest TFC. These differences can be due to the different chemical structures of the extracted components. Based on these results, HIW-45℃ was the optimal extraction method for Hermetia illucens. We intend to further investigate the availability of functional materials for Hermetia illucens using this method.

The present study investigated the feasibility of using the ethanolic extract of Hermetia illucens larvae (HIE) as a whitening improvement material. In cell viability assays using B16F1 melanoma cells, no cytotoxicity was recorded up to 200 μg·mL-1 of HIE. Moreover, while tyrosinase inhibitory activity increased, melanin content decreased in a dose-dependent manner, indicating that HIE likely inhibited tyrosine-induced intracellular melanin biosynthesis in B16F1 melanoma cells. Therefore, HIE is expected to serve as a potent whitening improvement material.