Graciela Valladares

Quantitative food webs of dipteran leafminers and their parasitoids in Argentina

The quantitative structure of two host–parasitoid communities based on leaf-mining flies (Diptera, Agromyzidae) in Argentina is described. The two communities consisted of 29 and 27 hosts, 46 and 40 parasitoids, and 193 and 179 recorded host–parasitoid associations. Also, food webs were constructed for one community based solely on samples taken in the wet and dry seasons. Data were expressed as quantitative food webs, and the manner in which food web properties, such as connectance and compartmentalization, were influenced by sampling intensity was explored. The potential importance of indirect effects between hosts mediated by parasitoids (e.g. apparent competition) was assessed using quantitative parasitoid overlap diagrams. The study’s results suggest that indirect effects are likely to be important in these highly connected communities. The limitations of the study’s analysis, and how the conclusions can be tested experimentally, are discussed.

A Moveable Feast: Insects Moving at the Forest-Crop Interface Are Affected by Crop Phenology and the Amount of Forest in the Landscape

Edges have become prevailing habitats, mainly as a result of habitat fragmentation and agricultural expansion. The interchange of functionally relevant organisms like insects occurs through these edges and can influence ecosystem functioning in both crop and non-crop habitats. However, very few studies have focused on the directionality of insect movement through edges, and the role of crop and non-crop amount has been ignored. Using bi-directional flight interception traps we investigated interchange of herbivore, natural enemy, pollinator and detritivore insects between native forest fragments and soybean crops, simultaneously considering movement direction, forest cover in the landscape and crop phenology. In total, 52,173 specimens and 877 morphospecies were collected. We found that, within most functional and taxonomic groups, movement intensity was similar (richness and/or abundance) between directions, whereas a predominantly forest-to-crop movement characterized natural enemies. Insect movement was extensively affected by crop phenology, decreasing during crop senescence, and was enhanced by forest cover particularly at senescence. Mainly the same herbivore species moved to and from the forest, but different natural enemy species predominated in each direction. Finally, our analyses revealed greater forest contribution to natural enemy than to herbivore communities in the crop, fading with distance to the forest in both groups. By showing that larger amounts of forest lead to richer insect interchange, in both directions and in four functional groups, our study suggests that allocation to natural and cultivated habitats at landscape level could influence functioning of both systems. Moreover, natural enemies seemed to benefit more than pests from natural vegetation, with natural enemy spillover from forests likely contributing to pest control in soybean fields. Thus consequences of insect interchange seem to be mostly positive for the agroecosystem, although consequences for the natural system deserve further study.

Parasitic assemblages on leafminers: a comparison of structure and function among host orders

In this study we ask whether parasitic complexes of leafminers display differences associated to host order, by comparing species number, taxonomic composition, parasitism rates and host ranges in parasitoid assemblages associated with lepidopteran and dipteran leafminers, in Chaco Serrano woodlands, central Argentina. Parasitoid assemblage size did not significantly differ between host orders, but dipteran hosts suffered higher parasitism rates. Lepidopteran hosts recruited a higher proportion of species and individuals of Braconidae, whereas dipteran leafminers were attacked by a higher proportion of Pteromalidae. We found clear effects of host taxonomic affiliation on the associated parasitoid fauna.

Natural vegetation cover in the landscape and edge effects: differential responses of insect orders in a fragmented forest.

Human activities have led to global simplification of ecosystems, among which Neotropical dry forests are some of the most threatened. Habitat loss as well as edge effects may affect insect communities. Here, we analyzed insects sampled with pan traps in 9 landscapes (at 5 scales, in 100–500 m diameter circles) comprising cultivated fields and Chaco Serrano forests, at overall community and taxonomic order level. In total 7043 specimens and 456 species of hexapods were captured, with abundance and richness being directly related to forest cover at 500 m and higher at edges in comparison with forest interior. Community composition also varied with forest cover and edge/interior location. Different responses were detected among the 8 dominant orders. Collembola, Hemiptera, and Orthoptera richness and/or abundance were positively related to forest cover at the larger scale, while Thysanoptera abundance increased with forest cover only at the edge. Hymenoptera abundance and richness were negatively related to forest cover at 100 m. Coleoptera, Diptera, and Hymenoptera were more diverse and abundant at the forest edge. The generally negative influence of forest loss on insect communities could have functional consequences for both natural and cultivated systems, and highlights the relevance of forest conservation. Higher diversity at the edges could result from the simultaneous presence of forest and matrix species, although “resource mapping” might be involved for orders that were richer and more abundant at edges. Adjacent crops could benefit from forest proximity since natural enemies and pollinators are well represented in the orders showing positive edge effects.

Chapter 5 Role of Melia azedarach L. (Meliaceae) for the control of insects and acari: present status and future prospects

Publisher Summary Various families of plants possess anti-insect compounds. From the Meliaceae family, insecticide molecules have been isolated, the limonoid azadirachtin obtained from Azadirachta indica or Melia azadirachta (neem) being the most potent and studied. Another tree belonging to the Meliaceae family, far less studied than the previously mentioned, is Melia azedarach . This chapter presents information about the active principles isolated by various investigators from M. azedarach together with their respective bioactivities. Moreover, the chapter describes the effects on feeding, growth, larval and pupal development, fecundity, fertility, toxic effects, as well as alterations in the insect morphology of different extracts.

The Invasive Liriomyza huidobrensis (Diptera: Agromyzidae): Understanding Its Pest Status and Management Globally

Liriomyza huidobrensis (Blanchard) is native to South America but has expanded its range and invaded many regions of the world, primarily on flowers and to a lesser extent on horticultural product shipments. As a result of initial invasion into an area, damage caused is usually significant but not necessarily sustained. Currently, it is an economic pest in selected native and invaded regions of the world. Adults cause damage by puncturing abaxial and adaxial leaf surfaces for feeding and egg laying sites. Larvae mine the leaf parenchyma tissues which can lead to leaves drying and wilting. We have recorded 365 host plant species from 49 families and more than 106 parasitoid species. In a subset of the Argentinian data, we found that parasitoid community composition attacking L. huidobrensis differs significantly in cultivated and uncultivated plants. No such effect was found at the world level, probably due to differences in collection methods in the different references. We review the existing knowledge as a means of setting the context for new and unpublished data. The main objective is to provide an update of widely dispersed and until now unpublished data, evaluate dispersion of the leafminer and management strategies in different regions of the world, and highlight the need to consider the possible effects of climate change on further regional invasions or expansions.

Something is lost and something is gained: loss and replacement of species and functional groups in ant communities at fragmented forests

ContextSmall fragments of natural habitats with an increased proportion of edges are common landscape traits following agricultural expansion. Consequences of habitat fragmentation are widely documented. However, functional and mechanistic approaches are still needed in order to understand these changes.ObjectivesWe studied habitat loss and edge effects on ant communities, addressing changes in species and functional group diversity, and the relative importance of β-diversity components.MethodsIn an endangered Neotropical forest, we sampled ants in edge and interior habitats using pitfall traps, during three summers (28 sites). We calculated taxonomic, phylogenetic and functional diversity and partitioned taxonomic and functional β-diversity into replacement and loss/gain components.ResultsWe found more species and functional groups at edge than interior habitats, and four species were edge indicators. Habitat loss negatively affected total abundance and that of particular functional groups (fungus-growers and cryptic species) but had a positive effect on taxonomic, phylogenetic and functional diversity as well as abundance of opportunists and predators. Species and functional group replacement drove β-diversity, being linked to habitat loss. However, interactions between habitat loss and edges explained the loss/gain of taxonomic and functional composition.ConclusionsFragmentation led to enriched ant communities at edges, possibly resulting from a higher influx of matrix species as edges become pervasive. This highlights the need to assess the spillover between habitats to understand its influence. Moreover, species replacement and the decrease of functional groups due to habitat loss could have an impact on ecosystem processes in which ants play an important role.