QSAR Study of Biologically Active Essential Oils against Beetles Infesting the Walnut in Catamarca, Argentina.

Essential oils from six species of aromatic plants collected in the Catamarca Province of Argentina were evaluated for their chemical composition and repellent and insecticidal activities against beetles of the genus Carpophilus (Coleoptera: Nitidulidae) and Oryzaephilus (Coleoptera: Silvanidae) that infest the local walnut production. Experimental data were analyzed using generalized estimating equations, with normal distribution and the identity link function. From the spectral information from the tested essential oils, we worked their molecular modeling as mixtures by developing mixture descriptors ( Dmix) that combined the molecular descriptor of each component in the mixture ( d i) and its relative concentration ( x i), i.e., Dmix = f( d i, x i). The application of chemoinformatic approaches determined that a combination of mixture descriptors related to molecular size, branchedness, charge distribution, and electronegativity were useful to explain the bioactivity profile against Carpophilus spp. and Oryzaephilus spp. The reported models were rigorously validated using stringent statistical parameters and essential oils reported with repellent activity against other beetle species from the Nitidulidae and Silvanidae families. This model confirmed each essential oil as a repellent with a comparable performance to the experimental reports.

Sugary secretions of wasp galls: a want-to-be extrafloral nectar?

Background and Aims: The most widespread form of protective mutualisms is represented by plants bearing extrafloral nectaries (EFNs) that attract ants and other arthropods for indirect defence. Another, but less common, form of sugary secretion for indirect defence occurs in galls induced by cynipid wasps. Until now, such galls have been reported only for cynipid wasps that infest oak trees in the northern hemisphere. This study provides the first evidence of galls that exude sugary secretions in the southern hemisphere and asks whether they can be considered as analogues of plants' EFNs. Methods: The ecology and anatomy of galls and the chemical composition of the secretion were investigated in north-western Argentina, in natural populations of the host trees Prosopis chilensis and P. flexuosa . To examine whether ants protect the galls from natural enemies, ant exclusion experiments were conducted in the field. Key Results: The galls produce large amounts of sucrose-rich, nectar-like secretions. No typical nectary and sub-nectary parenchymatic tissues or secretory trichomes can be observed; instead there is a dense vascularization with phloem elements reaching the gall periphery. At least six species of ants, but also vespid wasps, Diptera and Coleoptera, consumed the gall secretions. The ant exclusion experiment showed that when ants tended galls, no differences were found in the rate of successful emergence of gall wasps or in the rate of parasitism and inquiline infestation compared with ant-excluded galls. Conclusions: The gall sugary secretion is not analogous to extrafloral nectar because no nectar-producing structure is associated with it, but is functionally equivalent to arthropod honeydew because it provides indirect defence to the plant parasite. As in other facultative mutualisms mediated by sugary secretions, the gall secretion triggers a complex multispecies interaction, in which the outcome of individual pair-wise interactions depends on the ecological context in which they take place.

Revision of Plumarius Philippi 1873 (Hymenoptera: Chrysidoidea, Plumariidae) from Argentina north of Patagonia, with description of eighteen new species.

Twenty six species of Plumarius from Argentina north of Patagonia are revised. Eighteen new species: Plumarius politus sp. nov., P. sarophorus sp. nov., P. globulosus sp. nov., P. angulatus sp. nov., P. noa sp. nov., P. divergens sp. nov., P. malaris sp. nov., P. gracilior sp. nov., P. riojanus sp. nov., P. exophthalmus sp. nov., P. planatus sp. nov., P. albinervis sp. nov., P. truncatus sp. nov., P. mikrommatus sp. nov., P. obscurus sp. nov., P. gracilis sp. nov., P. fidalgoi sp. nov., and P. ocellulatus sp. nov. are described and illustrated. A new record for known species as well as a key to 26 known species in the region is given. A redescription of P. tumidulus Papp, 2000, which is the first record of the family Plumariidae from Uruguay, is done.

Extrafloral nectar fuels ant life in deserts.

Interactions mediated by extrafloral nectary (EFN)-bearing plants that reward ants with a sweet liquid secretion are well documented in temperate and tropical habitats. However, their distribution and abundance in deserts are poorly known. In this study, we test the predictions that biotic interactions between EFN plants and ants are abundant and common also in arid communities and that EFNs are only functional when new vegetative and reproductive structures are developing. In a seasonal desert of northwestern Argentina, we surveyed the richness and phenology of EFN plants and their associated ants and examined the patterns in ant-plant interaction networks. We found that 25 ant species and 11 EFN-bearing plant species were linked together through 96 pairs of associations. Plants bearing EFNs were abundant, representing ca. 19 % of the species encountered in transects and 24 % of the plant cover. Most ant species sampled (ca. 77 %) fed on EF nectar. Interactions showed a marked seasonal pattern: EFN secretion was directly related to plant phenology and correlated with the time of highest ant ground activity. Our results reveal that EFN-mediated interactions are ecologically relevant components of deserts, and that EFN-bearing plants are crucial for the survival of desert ant communities.

Revision of the ocellatus species-group of the genus Plumarius Philippi 1873 (Hymenoptera, Chrysidoidea, Plumariidae), with description of three new species from Argentina.

This contribution presents the study of species-group of Plumarius Philippi 1873, as the result of a survey of the morphological variation in males. The group is characterized by the large ocelli and transverse head. It consists of the following three new species: P. culminatus Diez, Fidalgo & Roig-Alsina, sp. nov., P. ocellatus Diez, Fidalgo & Roig-Alsina, sp. nov., and P. stangei Diez, Fidalgo & Roig-Alsina, sp. nov. A characterization of the group, descriptions, and illustrations are provided.