Tri-trophic movement of carotenoid pigments from host plant to the parasitoid of a caterpillar

Abstract

Insect parasitoids normally produce white colored eggs. Habrobracon gelechiae (Hymenoptera: Braconidae) is a gregarious ectoparasitoid of various caterpillars. We found that adult female H. gelechiae lays yellow colored eggs when its larvae developed from host larvae of Choristoneura rosaceana and Epiphyas postvittana (both Lepidoptera: Tortricidae) that were fed green plant leaves, but white colored eggs when these same host larvae species were fed non-plant diets. This study investigated the causes of egg color in H. gelechiae and the possible consequences in terms of parasitoid fitness resulting from differential egg color. Using high-performance liquid chromatography we demonstrated that the yellow coloration resulted from the uptake of carotenoid plant pigments (mainly lutein and β-carotene) that were initially ingested by the caterpillar larvae from plant leaves, later absorbed by the parasitoid larvae (F0) feeding on the host and carried over to the adult parasitoids, and finally translocated to the eggs (F1) of the parasitoids. The amount of plant pigments consumed by the parasitoid larvae (F0) affected the intensity of the yellow color of the parasitoid’s eggs (F1). Similarly, egg color was affected by the adult female parasitoids lifetime egg production and deposition rate. Further tests suggest that the observed differences in egg color did not have a genetic basis and did not affect egg viability or fitness. To our best knowledge, this is the first report of a tri-trophic and multi-stage translocation of carotenoid plant pigments in parasitoids. We discuss possible evolutionary significance and putative functions of the absorption of plant pigments by parasitoid species.