Insect cuticle or exoskeleton is a complex extracellular matrix formed primarily from structural polysaccharide chitin and protein, and it plays a critical role in protecting them from various environmental stresses and pathogenic infection. Despite of limited composition, insect cuticle has remarkably diverse mechanical properties, ranging from soft and flexible to hard and rigid. My research has been focusing on functional importance of the genes involved in chitin metabolism and cuticle tanning (sclerotization and pigmentation) to comprehensively understand the genetic, enzymatic as well as molecular mechanism underlying differentiation, development and formation of insect cuticular extracellular matrices.

Plants of the Salicacea genus have in common that they utilize phenolic glycosides, so called salicinoids, as protection against leaf chewing herbivores. The caterpillar Cerura vinula only feeds on poplar and willow trees that belong to the family of Salicacea. For this reason, Cerura vinula is viewed as a specialist herbivore that is adapted to the salicinoid defense. Taking advantage of chemical and biochemical techniques we want to trace the salicinoid metabolism pathway, the location of transformation and the involved enzymes. To gain insights into the salicinoid metabolism the caterpillars were put on a specially designed diet. It consisted either of one salicinoid in large excess or one 13C labelled compound, applied together with fresh poplar leaves. As a next step, we are going to identify the new compounds formed in the caterpillar by MS and NMR techniques. To determine the location and mechanism of the transformation we started with a dissection of the caterpillar and a check of the tissue pH value. Afterwards, we incubated the midgut, hindgut and salivary gland tissues with salicin as model substrate and analyzed the transformation products by LC-MS. The transformation products resulted from deglycosilation of the substrate and consecutive oxidation and conjugation of the aglycon. With the gained knowledge we then aimed to identify the enzymes, which are involved in the metabolism. We successfully proofed the existence of glucosidases in the midgut by isoelectric focusing and incubation of the gel with the model substrate 4-methylumbelliferyl β-D-glucopyranosid. Additionally, we performed RNA sequencing on the caterpillar tissue. The transcripts and enzymes involved in the salicinoid metabolism are currently analyzed. During our studies we could determine the mid gut as the place for the deglycosilaton, oxidation and conjugation of salicinoids. Further we identified a new for Cerura vinula undescribed metabolite and proofed the presence of β-glucosidases in the midgut.

The respiration rate of PH3 susceptible strain was significantly higher than the resistant strain. The results showed no significant effect of oxygen level on the respiration rate of both strains. Phosphine reduced the respiration rate of both strains when it was applied in average concentrations. However, the rate of respiration of the resistant beetles increased significantly under a high level of phosphine. The increase of respiration rate was associated with the higher emission of VOCs which prove the acceleration of metabolic processes to face the phosphine action for survival. Flat grain beetle Cryptolestes pusillus and rusty grain beetle C. ferrugineus are similar insect species, but only C. ferrugineus is capable to develop a high phosphine resistance. A direct immersion solid phase microextraction gas chromatography-mass spectrometry (DI-SPME-GCMS) technology has identified the different fatty acids from PH3 resistant and susceptible strain of Tribolium castaneum.