Distinctive anatomical and histochemical responses of Nothofagus obliqua (Mirb.) Oerst (Nothofagaceae) to two galling Pteromalidae (Hymenoptera: Chalcidoidea) in Chile

Abstract

Nothofagus obliqua (Nothofagaceae) is a native tree to Chile, which hosts at least seven gall morphotypes, two of them induced by Hymenoptera, Pteromalidae. The life cycle of these pteromalids, particularly the feeding activity of their larvae, has a high impact on host plant tissues toward new shapes and functions, leading the gall formation. The Pteromalidae genus are mostly parasitoids of other insects, rarely inducing galls. This rare phenomenon is herein addressed in two models of study, the galls induced by Espinosa nothofagi and Plastobelyta gallicola on N. obliqua in Chilean flora. We assume that the two pteromalids have a similar impact over their host plant tissues, inducing similar galls regarding their anatomical and histochemical profiles. Our results confirm that E. nothofagi induces a clavate bud gall (CG), but P. gallicola induces a stem globoid gall (GG) herein describeb for the first time. Our premise is not supported, because the CG follows the structural and histochemical patterns described for hymenopteran galls, but the GG is peculiarly different. The CG has concentric layers of specialized tissues around the larval chamber, where lipids, proteins, and starch accumulate, while starch, alkaloids, proanthocyanidins, and lignins accumulate in the outer tissue compartment. The GG is simpler than the CG on the anatomical basis as it does not develop specialized tissue layers, and in addition, it does not accumulate starch and proanthocyanidins in any tissue layers. The distinct anatomical and histochemical profiles of the two galls indicate the specific impact of E. nothofagi and P. gallicola in the inner tissue layers. The similarities of the outer tissue layers between the two galls relate to the host stem morphogenetical constraints and lower plasticity.