Insects, like other organisms, must deal with a wide variety of potentially challenging environmental factors during the course of their life. An important example of such a challenge is the phenomenon of oxidative stress. This review summarizes the current knowledge on the role of adipokinetic hormones (AKH) as principal stress responsive hormones in insects involved in activation of anti-oxidative stress response pathways. Emphasis is placed on an analysis of oxidative stress experimentally induced by various stressors and monitored by suitable biomarkers, and on detailed characterization of AKH’s role in the anti-stress reactions. These reactions are characterized by a significant increase of AKH levels in the insect body, and by effective reversal of the markers—disturbed by the stressors—after co-application of the stressor with AKH. A plausible mechanism of AKH action in the anti-oxidative stress response is discussed as well: this probably involves simultaneous employment of both protein kinase C and cyclic adenosine 3′,5′-monophosphate pathways in the presence of extra and intra-cellular Ca²⁺ stores, with the possible involvement of the FoxO transcription factors. The role of other insect hormones in the anti-oxidative defense reactions is also discussed.

Insect silk is made up of structural fibrous (fibroins) and sticky (sericins) proteins, and contains a few small peptides of hitherto unknown functions. We demonstrate that two of these peptides inhibit bacterial and fungal proteinases (subtilisin, proteinase K and pronase). These ‘silk proteinase inhibitors’ 1 and 2 (SPI 1 and 2) are produced in the middle section of the silk‐secreting glands prior to cocoon spinning and their production is controlled at transcription level. The full length cDNA of pre‐SPI 1 contains 443 nucleotides and encodes a peptide of 76 amino‐acid residues, of which 20 make up a signal sequence. The mature SPI 1 (6056.7 Da, 56 residues) is a typical thermostable Kunitz‐type proteinase inhibitor with Arg in P1 position. The cDNA of pre‐SPI 2 consists of 260 nucleotides and yields a putative secretory peptide of 58 amino‐acid residues. The functional SPI 2 (3993 Da, 36 residues) is a single‐domain Kazal‐type proteinase inhibitor with unique structural features: free segment of the N‐terminus is reduced to a single amino‐acid residue, lack of CysI and CysV precludes formation of the A‐ring and provides increased flexibility to the C‐ring, and absence of several residues around the normal position of CysV shortens and changes the α helix segment of the protein. The structure reveals that the length and arrangement of the B‐ring, including exposure of the P1 residue, and the position of the C‐terminus relative to the B‐loop, are essential for the activity of the Kazal‐type inhibitors.