Evolution of host plant adaptation in the crucifer-feeding specialist Pieris rapae.

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The association of Pierid butterflies with glucosinolate-containing plants began about 75 million years ago with a host shift from Fabales to Brassicales. The key innovation that allowed colonization of these plants was the gut nitrile-specifier protein that enables Pierid larvae to circumvent the harmful effects of the glucosinolate-myrosinase system by redirecting glucosinolate hydrolysis to nitrile instead of isothiocyanate formation. We found that metabolism of glucosinolate-derived aromatic nitriles in Pieris rapae larvae is associated with release of cyanide turning the mustard oil bomb into a cyanide bomb . As aromatic glucosinolates were the most widespread glucosinolates in ancient Brassicales, we hypothesize that the ability to detoxify high cyanide levels contributed to the primary host shift. In this project, we will compare the impact of a cyanogenic diet on performance and food choice of P. rapae and a set of generalist and specialist lepidopteran herbivores. We will elucidate the mode of cyanide detoxification in P. rapae. The enzymes involved in cyanogenesis and cyanide detoxification will be identified at a molecular level. Finally, we are going to compare the mode and efficiency of cyanide detoxification among Pierid species. The involvement of two different groups of plant chemical defenses in speciation of one group of herbivores has rarely been studied. The results of the project will enable a better understanding of the biochemical bases of insect herbivore adaptation to the complex chemistry of their host plants in a coevolutionary context.