Larval Feeding Behavior of Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) on its Host Plant, Solanum sisymbriifolium Lamarck (Solanaceae): Interaction with Trichomes

Abstract

Larvae and adults of Gratiana spadicea (Klug 1829) feed only on Solanum sisymbriifolium Lamarck (Solanaceae) leaves. Leaves of this host plant bear simple, glandular and non-glandular, and stellate trichomes. In this paper, we show that larvae avoid eating the stellate trichomes, which are removed, before mesophile ingestion. First and second instar larvae macerated the trichome rays to reach the mesophile, while older instars and the adults removed the entire trichomes. In double choice tests, leaf discs with none (shaved leaf discs), high (HD) and low density (LD) of stellate trichomes were offered to larvae and adults of G. spadicea. Both preferred shaved and LD discs over the HD type. For the HD discs, the mean distance among the trichomes in a given leaf was smaller than that of first instar larvae head capsule width, indicating that feeding sites cannot be accessed unless they remove the trichome rays. Larvae that fed on intact leaf discs suffered higher mortalities than those that fed on shaved discs. Thus, the data suggest that S. sisymbriifolium stellate trichomes impose life history costs, functioning as a barrier for G. spadicea feeding, mainly to first instar larvae. On the other hand, trichome removal and selection of feeding sites with lower trichome density allow these larvae to overcome such barriers.