Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2014
Publication Date: 2/3/2014
Citation: Wang, X., Wallis, C.M., Daane, K.M. 2014. Tri-trophic movement of carotenoid pigments from host plant to the parasitoid of a caterpillar. Journal of Insect Physiology. 61:58-65. Interpretive Summary: Habrobracon gelechiae is an insect parasitoid that attacks two important caterpillar pests: the native, widespread obliquebanded leafroller and the introduced, quarantined light brown apple moth. Unlike most other parasitoids, H. gelechiae produces yellow eggs that might confer survival advantages. However, the source and importance of the yellow egg trait were unclear. The yellow color found in H. gelechiae eggs was determined by this study to be plant-derived carotenoids (lutein and ß-carotene) that moved through the food web from plant to caterpillar to H. gelechiae. These carotenoids did not significantly improve measured egg fitness in this study, although trends were observed suggesting that long-term accumulation of carotenoids is beneficial to H. gelechiae. These findings improved understanding of the characteristic yellow egg trait of H. gelechiae parasitoids, which are highly effective parasitoids for controlling caterpillar pests of many different fruit and nut trees.
Technical Abstract: Insect parasitoids normally produce white-colored eggs. Habrobracon gelechiae (Hymenoptera: Braconidae) is a gregarious ectoparasitoid of various caterpillars that lays yellow eggs when its larvae developed on leaf-fed Choristoneura rosaceana and Epiphyas postvittana (both Lepidoptera: Tortricidae) caterpillars. However, H. gelechiae lays white eggs when its larvae were raised on artificial diet-fed caterpillars. This study examined the source and function of the yellow coloration of H. gelechiae eggs. High-performance liquid chromatography determined that yellow egg coloration resulted from uptake of carotenoid plant pigments (mainly lutein and ß-carotene) that originated from plant leaves. These plant carotenoids were ingested by caterpillars, absorbed by feeding parasitoid larvae, and eventually moved into parasitoid eggs. Parasitoid egg color was determined to not have a genetic basis. The yellow intensity of parasitoid eggs instead depended on the amount of carotenoids ingested by parasitoid larvae, the rate female parasitoids produced eggs, and the amount of carotenoid reserves present within adult parasitoid females. The presence of carotenoids did not affect egg viability or fitness. This study documented a tri-trophic and multi-stage translocation of carotenoid plant pigments from plants to parasitoid eggs.