Graciela Valladares

National University of Cordoba, Argentina | UNC · Faculty of of Exact, Physical and Natural Sciences

The food chain length represents how much energy reaches different trophic levels in food webs. Environmental changes derived from human activities have the potential to affect chain length. We explore how habitat area and edges affect chain length through: (1) a bottom‐up effect of abundance (‘pyramid hypothesis’); (2) the truncation of the highes...

1. In forest fragments, microclimatic conditions differ between interior and forest edges and also vary with geographical orientation. These microclimatic variations could affect plant-insect food webs and the ecological processes in which they are involved. 2. We evaluated the effects of microclimatic conditions, and the direct and indirect effect...

Edges between natural and cultivated habitats have become dominant elements of all terrestrial ecosystems. Interchanges of several groups of organisms, such as insects, occur through these edges, potentially affecting ecosystem functioning and conservation of species and communities of neighboring habitats. Different trap types are used for collect...

1. Geographical orientation affects the magnitude of microclimatic edge effects, mainly by altering the exposure to solar radiation. There is considerable evidence about the influence of microclimatic edge effects on organisms at the population level, but little is known about effects at the community level, and variations with edge geographical or...

Food webs offer a useful approach to the study of complex communities interacting across trophic levels, potentially linking community structure and ecosystem services such as biological control. Herbivore-parasitoid food webs are relevant for agricultural production, in terms of pests and their control. Here, we compare caterpillar-parasitoid food...

Forest fragmentation is a component of global change, with substantial impact on biodiversity and ecosystem functioning. Despite extensive evidence of forest fragmentation effects on above‐ground ecological processes, little is understood about its below‐ground effects. Abundance and richness of leaf litter fauna can be affected by forest fragmenta...

In fragmented forests the edges experience changes in microclimatic conditions, which are referred to as “abiotic edge effect”, and differ according to geographical orientation and season. These microclimatic changes could influence the development rate of the organisms (particularly for movement - restricted ones like leaf miner larvae and their p...

Context Small 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. Objectives We studied habitat loss and edg...

Essential oils, which are mixtures of terpenes, frequently show stronger insecticide activity, i.e., lower lethal dose 50 (LC50), than their most abundant terpenes. Synergy between terpenes provides a plausible explanation, but its demonstration has been elusive. In the present work, we look for an alternative explanation, by considering the influe...

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...

It is increasingly recognized that understanding the functional consequences of landscape change requires knowledge of aboveground and belowground processes and their interactions. For this reason, we provide novel information addressing insect herbivory and edge effects on litter quality and decomposition in fragmented subtropical dry forests in c...

Hunger plays a crucial role in insect feeding behavior, however food deprivation is rarely considered when insect responses to plant host and related chemical stimuli are investigated. Here we assessed, by means of experiments with Y-tube olfactometer, the effect of food deprivation time on the response of a specialist (Xanthogaleruca luteola) and...

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 nine landscapes (at five scales, in 100–500m diameter circles) comprising cultivated fields and...

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 m...

Movement intensity of natural enemies between forest and soybean crops. Richness (a) and abundance (b) of total natural enemies and their three main orders (Coleoptera, Diptera and Hymenoptera) moving toward crops (in green) and towards forest (in blue) at soybean phenological phases: vegetative, reproductive and senescence. (TIF)

Relationships between forest cover and detritivore movement. Significant relationships between forest cover in the landscape and movement of detritivore insects at soybean phenological phases: vegetative (green), reproductive (red) and senescence (blue). When differences between movement directions were significant, empty circles represent movement...

Movement intensity of herbivores between forest and soybean crops. Richness (a) and abundance (b) of total herbivores and the three main orders (Coleoptera, Hemiptera and Lepidoptera) moving toward crops (in green) and towards forest (in blue) at phenological phases of soybean (vegetative, reproductive, senescence). (TIF)

Relationships between forest cover and pollinator movement. Significant relationships between forest cover in the landscape and movement of pollinator insects at soybean phenological phases: vegetative (green), reproductive (red) and senescence (blue). Lines are used only when the relation with forest cover was significant. (a) Total pollinator ric...

Movement intensity of pollinators between forest and soybean crops. Richness (a) and abundance (b) of total and hymenopteran pollinators moving towards crops (in green) and towards forest (in blue) at soybean phenological phases: vegetative, reproductive and senescence. (TIF)

Movement intensity of detritivores between forest and soybean crops. Richness (a) and abundance (b) of total detritivores and the two main orders (Coleoptera, and Diptera) moving towards crops (in green) and towards forest (in blue) at soybean phenological phases: vegetative, reproductive and senescence. (TIF)

Relationships between forest cover and herbivore movement. Significant relationships between proportion of forest cover in the landscape and movement of herbivore insects at phenological phases of soybean: vegetative (green), reproductive (red) and senescence (blue). Tendency lines are used only when the relation with forest cover was significant....

Relationships between forest cover and natural enemy movement. Significant relationships between proportion of forest cover in the landscape and movement of natural enemies at soybean phenological phases: vegetative (green), reproductive (red) and senescence (blue). When differences between movement directions were significant, empty circles repres...

Summary of model selection by AICc. For each functional group and order, the best three models and the full model (which includes all independent variables and their paired interactions) are ind1icated. AICc values for every model and ΔAICc (difference in AICc between each model and the top model) are also included. x indicates interactions between...

Food webs are usually regarded as snapshots of community feeding interactions. Here, we describe the yearly and cumulative structure of parasitoid–caterpillar food webs on soybean in central Argentina, analyzing parasitism rates and their variability in relation to parasitoid diversity and food web vulnerability in the system. Lepidoptera larvae we...

Galling insects tend to be highly sensitive to changes in their host plants or their environment. Here we analyze the effects of Chaco Serrano forest fragmentation on gall inducing species associated with four native plants species, simultaneously examining area and edge effects as well as the role of host plant availability on such effects. At edg...

Studies on insect natural enemies and their effects on host populations are of immense practical value in pest management. Predation and parasitism on a citrus pest, the leafminer Phyllocnistis citrella Stainton, were evaluated by sampling over 3 years in four locations within a world leading lemon producing area in Northwest Argentina. Both mortal...

The expansion of agriculture has led to forest loss and fragmentation, resulting in dramatic biodiversity impoverishment. Surprisingly, few studies have assessed forest fragmentation effects on leaf‐cutting ant assemblages, and none has dealt with effects on their community richness and composition, despite their known role as key herbivores and ec...

The increase in cultivated lands has led to ecosystem and biodiversity loss. Arthropod natural enemies, involved in the ecosystem service of biological control, benefit from non‐crop habitat and may be affected by its proximity and amount in the landscape. We have evaluated natural enemy richness and composition in relation to forest cover in the l...

Habitat fragmentation can alter fundamental ecological interactions such as insect herbivory. Few studies of habitat fragmentation effects on herbivory have examined the mechanisms involved, and differences among insect guilds have been largely ignored. Here, we studied area and edge effects on herbivory by three guilds of phytophagous insects in a...

Loss and fragmentation of natural ecosystems are widely recognized as the most important threats to biodiversity conservation, with Neotropical dry forests among the most endangered ecosystems. Area and edge effects are major factors in fragmented landscapes. Here, we examine area and edge effects and their interaction, on ensembles of arthropods a...

Worldwide, intense forest fragmentation has resulted in mosaic landscapes in which biodiversity and a number of important ecological processes are threatened. Insect parasitism is a vital component of herbivore population regulation, hence the study of parasitism and parasitoid richness in fragmented forests embedded in an agricultural matrix is re...

Abstract Many terrestrial ecosystems are changing due to extensive land use and habitat fragmentation, posing a major threat to biodiversity. In this study, the effects of patch size, isolation, and edge/interior localization on the ground dwelling insect communities in the Chaco Serrano woodland remnants in central Argentina were examined. Samplin...

Although there is accumulating evidence from artificially assembled communities that reductions of species diversity result in diminished ecosystem functioning, it is not yet clear how real-world changes in diversity affect the flow of energy between trophic levels in multi-trophic contexts. In central Argentina, forest fragmentation has led to spe...

Fragmentation and loss of habitat are critical components of the global change currently threatening biodiversity and ecosystem functioning. We studied the effects of habitat loss through fragmentation on food web structure, by constructing and analyzing plant-herbivore and host-parasitoid food webs including more than 400 species and over 120 000...

Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-fre...

Las "moscas minadoras" se caracterizan por excavar túneles (�minas�) en el interior de las hojas, consumiendo el mesófilo y dejando intacta la epidermis foliar o, al menos, su pared externa. Hay especies cuyas larvas, en lugar de realizar estas galerías en las hojas, viven y se alimentan en el interior de otros tejidos vegetales, barrenando tallos,...

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 di...

1. Biological communities are organized in complex interaction networks such as food webs, which topology appears to be non-random. Gradients, compartments, nested subsets and even combinations of these structures have been shown in bipartite networks. However, in most studies only one pattern is tested against randomness and mechanistic hypotheses...

La fragmentación de hábitats, mediada por los cambios en uso de la tierra, constituye una de las principales amenazas a la biodiversidad del planeta. En una comunidad, las especies se encuentran conectadas mediante relaciones tróficas que componen complejas redes de interacción. Debido a esto, los cambios en abundancia o pérdida de especies pueden...

RESUMEN En la actualidad, la mayoría de los ecosistemas terrestres están siendo drásticamente modificados por la pérdida y fragmen-tación del hábitat. Estudios previos, realizados en fragmentos de hábitat del Chaco Serrano, revelaron que se producen cam-bios en la comunidad de invertebrados de suelo asociados a la fragmentación. Para evaluar si est...

Phytochemical induction of monoterpenes following herbivory by insects and mechanical damage, was studied in Minthostachys mollis (Lamiaceae), a plant native to Central Argentina with medicinal and aromatic uses in the region. The monoterpenes pulegone and menthone were analyzed in M. mollis 24 and 48 h after leaves were mechanically damaged or exp...

Host preferences of phytophagous insects, although generally showing a strong hereditary component, can be modified by experience. Here we aim to elucidate the relative roles of larval and adult experience on host plant selection by Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae), a widely distributed pest on ornamentals and vegetables. L...

We examined the effects of the flavonoids pinocembrin and quercetin on the feeding behavior, survival, and development of the Cucurbitaceae pest Epilachna paenulata (Coleoptera: Coccinellidae). In no-choice experiments, 48 hr-consumption of Cucurbita maxima Duch. leaves treated with pinocembrin at 1, 5, and 50 microg/cm(2) was less than one third o...

1. The spatial structure of plant patches has been shown to affect host–parasitoid interactions, but its influence on parasitoid diversity remains largely ignored. Here we tested the prediction that parasitoid species richness of the specialist leafminer Liriomyza commelinae increases in larger and less isolated patches of its host plant Commelina...

Body size of polyphagous parasitoids of agromyzid leafminers directly depends on that of their hosts. The possible influence of plant host on parasitoid body size was studied for the pea leafminer, Liriomyza huidobrensis Blanchard, and three of its most abundant solitary parasitoids: Phaedrotoma scabriventris (Nixon) (Braconidae), Halticoptera heli...

Not all species are likely to be equally affected by habitat fragmentation; thus, we evaluated the effects of size of forest remnants on trophically linked communities of plants, leaf-mining insects, and their parasitoids. We explored the possibility of differential vulnerability to habitat area reduction in relation to species-specific and food-we...

The relationship between preference and performance is crucial to the ecology and evolution of plant–insect interactions. Oviposition preference and offspring performance were evaluated for a citrus pest, the leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae), on three of its host plants: lemon (Citrus limon L. Burm.), orange (Citrus si...

En la búsqueda de compuestos botánicos con potencial uso insecticida, se evaluó la actividad de extractos de fruto maduro y hojas senescentes de Melia azedarach L. (2, 5 y 10%), sobre larvas de Spodoptera eridania Cramer (Lepidoptera: Noctuidae) especie polífaga considerada plaga esporádica de importantes cultivos. Mediante pruebas de elección, se...

Aedes aegypti (L.) (Diptera: Culicidae), the main urban vector of dengue, has developed resistance to various insecticides, making its control increasingly difficult. We explored the effects of Argentine Melia azedarach L. (Meliaceae) fruit and senescent leaf extracts on Ae. aegypti larval development and survival, by rearing cohorts of first insta...

200 of 1137 species of British microlepidoptera make a single marked change in feeding habit as they grow. Most numerous are species that change from leaf mining to one of case bearing, spinning, tying and rolling or concealed feeding, and species that change from concealed feeding to case bearing or spinning, tying and rolling. Although in some in...

The possibility of interactions between leaf‐miners in the genus Eriocrania and Coleophora serratella L. on birch ( Betula pendula Ehrh. and B.pubescens Roth.) was studied via: (i) co‐occurrence patterns on random samples of leaves; (ii) palatability of Eriocraniidae‐mined leaves to C.serratella , in laboratory and field preference tests. In the fi...

In the course of searching for plant chemicals with potential insecticide properties, the activity of Melia azedarach L. senescent leaf and ripe fruit extracts (2, 5 and 10%) was evaluated on larvae of Spodoptera eridania Cramer (Lepidoptera: Noctuidae). This polyphagous species is considered a sporadic pest on many important crops. Food consumptio...

Aerial parts of 27 plant species native to Argentina were tested in anti-insect, germination inhibition and bactericide bio-assays. In antifeedant assays on Epilachna paenulata larvae, 11 species showed strong feeding deterrent effects (higher than 90% at 200 microg/cm(2)). Twelve plants strongly inhibited the germination of Avena sativa seeds, but...

Leafminers are insects whose larvae live and feed within plant leaves, consuming mesophyll tissue without damaging the leaf epidermis. Several species are considered serious pests on intensive, horticultural, and ornamental crops. Natural enemies are the most frequent source of mortality for this herbivore insect guild, with parasitoids being the m...

Leafminers are insects whose larvae live and feed within plant leaves, consuming mesophyll tissue without damaging the leaf epidermis. Several species are considered serious pests on intensive, horticultural, and ornamental crops. Natural enemies are the most frequent source of mortality for this herbivore insect guild, with parasitoids being the m...

Egg extrusion patterns were investigated as an inducible defensive mechanism in potato plants against the leafminer Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae). Increased multiplication rates in leaf cells surrounding an egg of L. huidobrensis leads to its exposure through the leaf cuticle, which might increase the risk of mortality....

Plant defensive mechanisms against herbivores include chemical changes following damage. Effects of feeding punctures produced by Liriomyza huidobrensis (pea leafminers) adult females on the plant's dominant monoterpenes, pulegone and menthone were assessed by monitoring essential oil composition at 24, 48, and 120 h; emission of volatiles was also...

In laboratory choice and no-choice bioassays, treatment of elm leaves with extracts obtained from unripe fruits and green or senescent leaves of Melia azedarach at 1-10% concentration significantly deterred feeding by adults of the elm leaf beetle, Xanthogaleruca luteola. Also, in no-choice tests, adults fed on leaves treated with 2, 5 or 10% extra...

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 Me...

The optimal oviposition theory predicts that oviposition preferences of phytophagous insects should correlate with host suitability for their offspring. As plant host suitability depends not only on its quality as food, but also on its provision of enemy-free space, we examined the relationship between adult host preference and offspring performanc...