Juan Pablo Torretta

Effects of agriculture expansion and intensification on the vertebrate and invertebrate diversity in the Pampas of Argentina

In this paper we summarize for the first time the effects of agriculture expansion and intensification on animal diversity in the Pampas of Argentina and discuss research needs for biodiversity conservation in the area. The Pampas experienced little human intervention until the last decades of the 19th century. Agriculture expanded quickly during the 20th century, transforming grasslands into cropland and pasture lands and converting the landscape into a mosaic of natural fragments, agricultural fields, and linear habitats. In the 1980s, agriculture intensification and replacement of cattle grazing-cropping systems by continuous cropping promoted a renewed homogenisation of the most productive areas. Birds and carnivores were more strongly affected than rodents and insects, but responses varied within groups: (a) the geographic ranges and/or abundances of many native species were reduced, including those of carnivores, herbivores, and specialist species (grassland-adapted birds and rodents, and probably specialized pollinators), sometimes leading to regional extinction (birds and large carnivores), (b) other native species were unaffected (birds) or benefited (bird, rodent and possibly generalist pollinator and crop-associated insect species), (c) novel species were introduced, thus increasing species richness of most groups (26% of non-rodent mammals, 11.1% of rodents, 6.2% of birds, 0.8% of pollinators). Much taxonomic and ecological work is still needed to understand Pampean animal biodiversity, to understand how agriculturization is affecting it, and to identify appropriate conservation actions. Networks of Important Bird Areas and Valuable Grassland Areas harbor a balanced representation of Pampean biodiversity and, if adequately protected, may provide valuable research sites, but complementary work should be carried out on agriculturized areas.

First record of the invasive bumblebee Bombus terrestris (L.) (Hymenoptera, Apidae) in Argentina

Abstract A recent (March 2006) field survey of plant-pollinator interactions in North Patagonia, Argentina, revealed the presence of Bombus terrestris as flower visitors to several plant species in a natural environment. This is the first record of this invasive bumblebee in Argentina. The available evidence suggests that B. terrestris entered Argentina from Chile, where it was introduced in 1998, through low-altitude passes across the Andes.

Elaiophores in Gomesa bifolia (Sims) M.W. Chase & N.H. Williams (Oncidiinae: Cymbidieae: Orchidaceae): structure and oil secretion

BACKGROUND AND AIMS Oils are an unusual floral reward in Orchidaceae, being produced by specialized glands called elaiophores. Such glands have been described in subtribe Oncidiinae for a few species. The aims of the present study were to identify the presence of elaiophores in Gomesa bifolia, to study their structure and to understand how the oil is secreted. Additionally, elaiophores of G. bifolia were compared with those of related taxa within the Oncidiinae. METHODS Elaiophores were identified using Sudan III. Their structure was examined by using light, scanning electron and transmission electron microscopy. KEY RESULTS Secretion of oils was from the tips of callus protrusions. The secretory cells each had a large, centrally located nucleus, highly dense cytoplasm, abundant plastids containing lipid globules associated with starch grains, numerous mitochondria, an extensive system of rough and smooth endoplasmatic reticulum, and electron-dense dictyosomes. The outer tangential walls were thick, with a loose cellulose matrix and a few, sparsely distributed inconspicuous cavities. Electron-dense structures were observed in the cell wall and formed a lipid layer that covered the cuticle of the epidermal cells. The cuticle as viewed under the scanning electron microscope was irregularly rugose. CONCLUSIONS The elaiophores of G. bifolia are of the epithelial type. The general structure of the secretory cells resembles that described for other species of Oncidiinae, but some unique features were encountered for this species. The oil appears to pass through the outer tangential wall and the cuticle, covering the latter without forming cuticular blisters.

Species diversity of entomophilous plants and flower-visiting insects is sustained in the field margins of sunflower crops

Field margins are key landscape features sustaining biodiversity in farmland mosaics and through that, ecosystem services. However, agricultural intensification has encouraged fencerow removal to enlarge cropping areas, reducing farmland biodiversity and its associated ecosystems services. In the present work, we assess the role of field margins in retaining farmland biodiversity across the sunflower cropping area of Argentina. Flower-visiting insects and entomophilous plants were intensively sampled along the margins of sunflower fields, in eight locations across eastern Argentina. We recorded 149 species of flowering plants and 247 species of flower-visitors. Plants and arthropods were mostly natives. Most of the floral visitors captured provide ecosystem services to agriculture. Our results show that many species of beneficial insects and native plants occur in semi-natural linear features in the intensively managed farmland of Argentina. Field margins may constitute the last refugia of native plant species and their associated fauna in farmland mosaics. Conservation of field margins in Argentine farmland may therefore be essential for preserving biodiversity and associated ecosystem services.

The Sarcophagidae (Diptera) of the Coastline of Buenos Aires City, Argentina

Abstract The flesh fly community was surveyed on the shoreline of Río de la Plata at an ecological reserve whose western border directly abuts downtown eastern Buenos Aires. Samples were taken at monthly intervals from September 2004 to August 2005. To attract the flies, dog faeces and rotten cow liver were used as bait. Overall number, species composition and sex ratio were referred to each chosen bait. Of the thirteen species captured during the sampling period, Helicobia aurescens (Townsend), Oxysarcodexia culmiforceps Dodge, Oxysarcodexia marina (Hall), Oxysarcodexia thornax (Walker), Sarcophaga (Lipoptilocnema) koehleri (Blanchard), S. (L.) lanei (Townsend) and Tricharaea (Sarcophagula) occidua (Fabricius) were recorded for the first time in Buenos Aires city. Regardless of species composition, higher number of flies were obtained on faeces. Tricharaea (S.) occidua, was highly dominant (78,35%) followed in abundance by Oxysarcodexia varia (7,82%), both species showing a strong preference for dog faeces. Microcerella muehni and Oxysarcodexia paulistanensis did not show any preference on either bait. Sex ratio was male biased for O. varia, while females were dominant for O. paulistanensis and T. (S.) occidua, and no differences were found for M. muehni. Baits preference and sex ratio could not be estimated for the remaining species due to their low abundance.

Diversity and life-history traits of wild bees (Insecta: Hymenoptera) in intensive agricultural landscapes in the Rolling Pampa, Argentina

ABSTRACT The decline of bees is a major concern due to their vital role in pollinating many crops and wild plants. Some regions in South America, and especially the Pampas, are amongst those parts of the world where stressors of bee populations have been little studied. The Pampas has been intensively transformed for agriculture, being presently one of the most productive areas of agricultural commodities in the world. Here, we aim to provide first insights on the taxonomic and functional composition of bee assemblages in the Rolling Pampa, the most intensively managed part of the Pampas. Soybean (herbicide-tolerant genetically modified varieties) is the predominant crop in this region. Bees were sampled with coloured pan traps. Sampling points were located on field margins in either the cropped or the semi-natural grassland area of a farmland site devoted to annual cropping. A total of 2384 individuals were caught, representing 33 taxa [mainly (morpho)species]. The subgenus Lasioglossum (Dialictus) largely dominated captures (78% of the total abundance) and was relatively abundant in the entire study area, suggesting that some species are likely to reach their ecological requirements in cropped areas. No-till fields and field margins may provide large areas for these below-ground nesting species, while their polylectic food preferences allow them to collect pollen on a wide range of plant species, among them possibly soybean. On the contrary, the richness and the abundance of other taxa were higher in the semi-natural area than in the cropped area. Among them, above-ground nesting or oil-collecting species, which have more specialised nesting and floral requirements, were highly associated with the semi-natural area. Our findings highlight the large dominance of L. (Dialictus) species in this highly intensively managed landscape, and the urgent need of preserving semi-natural habitats to maintain species-rich and functionally diverse bee communities in the Pampas.

Nesting ecology of Megachile (Chrysosarus) catamarcensis Schrottky (Hymenoptera: Megachilidae), a Prosopis-specialist bee

Summary Nests of the leafcutting bee Megachile (Chrysosarus) catamarcensis Schrottky (Hymenoptera: Megachilidae) were obtained during a 24 month trap-nesting programme in a xeric forest in the Province of La Pampa, Argentina. Nests were constructed in December and January; females made an average of 4.0 ± 2.2 cells, and used mud with flower petals and/or leaf pieces to build their nests. Provisions of cells were practically pure pollen mass of Proposis caldenia. Adult emergence showed a unimodal pattern, suggesting a univoltine life cycle. However, two individuals that emerged a month after the traps were collected indicate the existence of a small early-summer generation. This could indicate that M. catamarcensis, in some years (warmer) or in some populations (at lower latitudes), could exhibit a bivoltine life cycle. Approximately 15.3 % of all offspring failed to complete development to the adult stage, and an additional 13.9 % were killed by natural enemies. These included diverse parasitic wasps (Chrysididae, Sapygidae, and Leucospidae), a cleptoparasite bee (Megachilidae: Coelioxys), and a bee fly (Bombyliidae: Antrhax).

Life cycle of Huarpea fallax (Hymenoptera: Sapygidae) in a xeric forest in Argentina

This study describes the life cycle of Huarpea fallax (Hymenoptera: Sapygidae) in a xeric forest in La Pampa province, Argentina. This cleptoparasitic wasp attacks the nests of two species of leaf-cutter bees: Megachile catamarcensis and Anthidium vigintipunctatum, both belonging to the family Megachilidae. Nests of these bee species were obtained during a trap-nesting programme. Adult emergence showed a unimodal pattern indicating a univoltine life cycle. The period from egg-laying to adult emergence lasted for 10–13 months; however, one female took about 2 years to emerge, suggesting parsivoltinism. Most females attack one cell per host nest, the outermost cells being the ones most parasitized. However, the position of the attacked cells was variable. In this paper, although there were insufficient data to prove a correlation, the data suggest a positive trend between body size of sapygid wasps and their host bees.

Reproductive biology of Setaria magna Griseb. (Poaceae: Panicoideae: Paniceae)

The genus Setaria is economically important because many species are cultivated for grains or forage. Setaria magna is an American species, native to North America and introduced in South America. The morphological aspect of this species is similar to S. italica (foxtail millet), suggesting its potential value as a crop. The purpose of this work was to understand the breeding system (self-pollination vs. open pollination) of S. magna; additionally, the floral development was described. The results of the breeding system analysis indicated that S. magna is mainly autogamous and does not appear to have a self-incompatibility mechanism. The floral development observed was similar to that described for other Paniceae; in most of the spikelets only the upper anthecium developed fruit, but a small number of spikelets presented bisexual lower florets. These spikelets produced two caryopses per spikelet. Thus, S. magna can produced two types of dispersal units; a few whitish naked caryopses from the lower anthecium that fall without their lemma and palea at maturity; and a high number of brown caryopses protected by the lemma and palea from the upper anthecium. The presence of a normal embryo sac in the upper anthecium suggests that S. magna would present normal sexual reproduction, although we can not reject the formation of apomitic seeds in the lower anthecium.

The reproduction of Colletia hystrix and late-flowering in Colletia (Rhamnaceae: Colletieae)

Plant fitness strongly depends on the timing of flower production. In temperate climates most plants bloom during a relatively well-defined peak, while comparatively few species flower before or after the community peak. Since a phylogenetical signal has been shown to exist in the determination of reproductive phenology, it is of interest to identify characters associated with the emergence of either type of behaviour. Here we report on the reproduction of the late-flowering shrub Colletia hystrix and discuss the results in the context of the whole genus Colletia. Colletia hystrix shares with its congeners deep flowers, associated with assemblages of long-mouthpart pollinators, and characters that maximise the chances of successful pollen receipt and export in a single pollinator visit (homogamy, a large stigma, and an extragynoecial compitum). Leaflessness and extreme spinescence of Colletia are suggested to be related (via compromised resource acquisition) to phenological displacement and its flower-level correlates.