This thesis focuses on flavonoids, a subgroup of phenolic compounds produced by

plants, and how they affect the herbivorous larvae of lepidopterans and sawflies. The

first part of the literature review examines different techniques to analyze the chemical

structures of flavonoids and their concentrations in biological samples. These techniques

include, for example, ultraviolet-visible spectroscopy, mass spectrometry, and

nuclear magnetic resonance spectroscopy. The second part of the literature review

studies how phenolic compounds function in the metabolism of larvae. The harmful

oxidation reactions of phenolic compounds in insect guts are also emphasized. In addition

to the negative effects, many insect species have evolved the use of phenolic

compounds for their own benefit.

In the experimental part of the thesis, high concentrations of complex flavonoid oligoglycosides

were found in the hemolymph (the circulatory fluid of insects) of birch

and pine sawflies. The larvae produced these compounds from simple flavonoid precursors

present in the birch leaves and pine needles. Flavonoid glycosides were also

found in the cocoon walls of sawflies, which suggested that flavonoids were used in

the construction of cocoons. The second part of the experimental work studied the

modifications of phenolic compounds in conditions that mimicked the alkaline guts of

lepidopteran larvae. It was found that the 24 plant species studied and their individual

phenolic compounds had variable capacities to function as oxidative defenses in alkaline

conditions. The excrements of lepidopteran and sawfly species were studied to see

how different types of phenolics were processed by the larvae. These results suggested

that phenolic compounds were oxidized, hydrolyzed, or modified in other ways during

their passage through the digestive tract of the larvae.