Although the regulation of vitellogenesis in insects has been mainly discussed in terms of ‘classical’ lipid hormones, juvenile hormone (JH), and 20-hydroxyecdysone (20E), recent data support the notion that this process must be adjusted in harmony with a nutritional input/reservoir and involvement of certain indoleamines and neuropeptides in regulation of such process. This study focuses on crosstalks among these axes, lipid hormones, monoamines, and neuropeptides in regulation of vitellogenesis in the American cockroach Periplaneta americana with novel aspects in the roles of arylalkylamine N-acetyltransferase (aaNAT), a key enzyme in indoleamine metabolism, and the enteroendocrine peptides; crustacean cardioactive peptide (CCAP) and short neuropeptide F (sNPF). Double-stranded RNA against aaNAT (dsRNA^aaNAT) was injected into designated-aged females and the effects were monitored including the expressions of aaNAT itself, vitellogenin 1 and 2 (Vg1 and Vg2) and the vitellogenin receptor (VgR) mRNAs, oocyte maturation and changes in the hemolymph peptide concentrations. Effects of peptides application and 20E were also investigated. Injection of dsRNA^aaNAT strongly suppressed oocyte maturation, transcription of Vg1, Vg2, VgR, and genes encoding JH acid- and farnesoate O-methyltransferases (JHAMT and FAMeT, respectively) acting in the JH biosynthetic pathway. However, it did not affect hemolymph concentrations of CCAP and sNPF. Injection of CCAP stimulated, while sNPF suppressed oocyte maturation and Vgs/VgR transcription, i.e., acting as allatomedins. Injection of CCAP promoted, while sNPF repressed ecdysteroid (20E) synthesis, particularly at the second step of Vg uptake. 20E also affected the JH biosynthetic pathway and Vg/VgR synthesis. The results revealed that on the course of vitellogenesis, JH- and 20E-mediated regulation occurs downstream to indoleamines- and peptides-mediated regulations. Intricate mutual interactions of these regulatory routes must orchestrate reproduction in this species at the highest potency.

Efficiency of caffeic acid (CA) on Spodoptera littoralis was investigated. CA was mixed with artificial diet, and feeding indices and allatostatin-A (AST-A) content of the midgut were measured 10 days later. α-Amylase and protease activities were evaluated for 10 days. CA significantly decreased feeding indices. Feeding on an artificial diet containing CA decreased protease and α-amylase activities in the midgut. The incubation of the dissected midgut with AST-A increased α-amylase and protease activities. The injection of AST-A into the hemolymph of larvae also increased protease and α-amylase activities. Competitive ELISA and immunohistochemistry results showed that starvation decreased the AST-A titer and AST-A immunoreactivity (AST-A-ir) cells in the midgut whereas refeeding increased it. Here, for the first time we showed that feeding on an artificial diet containing CA also caused the AST-A level to decrease in the midgut, which itself caused α-amylase and protease activities to decrease.