Host plants of the polyphagous grapevine moth Lobesia botrana during larval stage modulate moth egg quality and subsequent parasitism by the parasitoid Trichogramma cacoeciae

Abstract

The European grapevine moth Lobesia botrana is the main pest in viticulture, and recently extended its area to South and North America. Biological control by egg parasitoids is a current issue, which may help achieving pesticide use reduction in grapes. We hypothesized that the host plant bearing the larvae of this polyphagous moth species could affect the egg quality produced by the adults with consequences on the egg parasitism by the egg parasitoid Trichogramma cacoeciae Marchal. Larval food of agar based supplemented with different host berries or flowers has been proposed to L. botrana larvae. Berries of two grape cultivars, Cabernet Franc and Sauvignon, and flowers of three host plants of L. botrana, Olive tree ( Olea europea), privet ( Ligustrum vulgare) and tansy ( Tanacetum vulgare), have been offered to larvae during their entire development, and eggs laid were exposed to T. cacoeciae females under laboratory controlled conditions. Results indicated an influence of the food offered to L. botrana larvae on the parasitism rate of their eggs by T. cacoeciae females. The rearing medium containing Sauvignon berries led to host eggs significantly less parasitized than those produced by L. botrana females raised on the other plants. Moreover, the percentage of aborted L. botrana eggs also differed and was the highest with the media containing Sauvignon berries. Our results suggest that host plant compounds ingested by the larvae could be stored in the eggs and affect their quality or viability. Finally, we observed that the presence of T. cacoeciae females significantly increased by two fold the percentage of aborted eggs compared to eggs with no female in the control treatment. Implications of these results in the biological control of L. botrana by Trichogramma species are discussed, especially for vineyards planted with different grape cultivars or surrounded by different vegetation.