Development of specific ITS markers for plant DNA identification within herbivorous insects

DNA based techniques have proved to be very useful methods to study trophic relationships 17 between pests and their natural enemies. However, most predators are best defined as omnivores, 18 and the identification of plant-specific DNA should also allow the identification of the plant 19 species the predators have been feeding on. In this study, a PCR approach based on the 20 development of specific primers was developed as a self-marking technique to detect plant DNA 21 within the gut of one heteropteran omnivorous predator (Macrolophus pygmaeus) and two 22 lepidopteran pest species (Helicoverpa armigera and Tuta absoluta). Specific tomato primers 23 were designed from the ITS 1-2 region, which allowed the amplification of a tomato DNA 24 fragment of 332 bp within the three insect species tested in all cases (100% of detection at t = 0) 25 and did not detect DNA of other plants nor of the starved insects. Plant DNA half-lives at 25ºC 26 ranged from 5.8h, to 27.7h and 28.7h within M. pygmaeus, H. armigera and T. absoluta, 27 respectively. Tomato DNA detection within field collected M. pygmaeus suggests dietary mixing 28 in this omnivorous predator and showed a higher detection of tomato DNA in females and 29 nymphs than males. This study provides a useful tool to detect and to identify plant food sources 30 of arthropods and to evaluate crop colonization from surrounding vegetation in conservation 31 biological control programs.

Differential effectiveness of microbially induced resistance against herbivorous insects in Arabidopsis.

Rhizobacteria-induced systemic resistance (ISR) and pathogen-induced systemic acquired resistance (SAR) have a broad, yet partly distinct, range of effectiveness against pathogenic microorganisms. Here, we investigated the effectiveness of ISR and SAR in Arabidopsis against the tissue-chewing insects Pieris rapae and Spodoptera exigua. Resistance against insects consists of direct defense, such as the production of toxins and feeding deterrents and indirect defense such as the production of plant volatiles that attract carnivorous enemies of the herbivores. Wind-tunnel experiments revealed that ISR and SAR did not affect herbivore-induced attraction of the parasitic wasp Cotesia rubecula (indirect defense). By contrast, ISR and SAR significantly reduced growth and development of the generalist herbivore S. exigua, although not that of the specialist P. rapae. This enhanced direct defense against S. exigua was associated with potentiated expression of the defense-related genes PDF1.2 and HEL. Expression profiling using a dedicated cDNA microarray revealed four additional, differentially primed genes in microbially induced S. exigua-challenged plants, three of which encode a lipid-transfer protein. Together, these results indicate that microbially induced plants are differentially primed for enhanced insect-responsive gene expression that is associated with increased direct defense against the generalist S. exigua but not against the specialist P. rapae.

A general model for host plant selection in phytophagous insects

We develop a general theoretical framework for exploring the host plant selection behaviour of herbivorous insects. This model can be used to address a number of questions, including the evolution of specialists, generalists, preference hierarchies, and learning. We use our model to: (i) demonstrate the consequences of the extent to which the reproductive success of a foraging female is limited by the rate at which they find host plants (host limitation) or the number of eggs they carry (egg limitation); (ii) emphasize the different consequences of variation in behaviour before and after landing on (locating) a host (termed pre- and post-alighting, respectively); (iii) show that, in contrast to previous predictions, learning can be favoured in post-alighting behaviour-in particular, individuals can be selected to concentrate oviposition on an abundant low-quality host, whilst ignoring a rare higher-quality host; (iv) emphasize the importance of interactions between mechanisms in favouring specialization or learning. (C) 2002 Elsevier Science Ltd.

Contrasting Effects Of Land Use Intensity And Exotic Host Plants On The Specialization Of Interactions In Plant-herbivore Networks.

Human land use tends to decrease the diversity of native plant species and facilitate the invasion and establishment of exotic ones. Such changes in land use and plant community composition usually have negative impacts on the assemblages of native herbivorous insects. Highly specialized herbivores are expected to be especially sensitive to land use intensification and the presence of exotic plant species because they are neither capable of consuming alternative plant species of the native flora nor exotic plant species. Therefore, higher levels of land use intensity might reduce the proportion of highly specialized herbivores, which ultimately would lead to changes in the specialization of interactions in plant-herbivore networks. This study investigates the community-wide effects of land use intensity on the degree of specialization of 72 plant-herbivore networks, including effects mediated by the increase in the proportion of exotic plant species. Contrary to our expectation, the net effect of land use intensity on network specialization was positive. However, this positive effect of land use intensity was partially canceled by an opposite effect of the proportion of exotic plant species on network specialization. When we analyzed networks composed exclusively of endophagous herbivores separately from those composed exclusively of exophagous herbivores, we found that only endophages showed a consistent change in network specialization at higher land use levels. Altogether, these results indicate that land use intensity is an important ecological driver of network specialization, by way of reducing the local host range of herbivore guilds with highly specialized feeding habits. However, because the effect of land use intensity is offset by an opposite effect owing to the proportion of exotic host species, the net effect of land use in a given herbivore assemblage will likely depend on the extent of the replacement of native host species with exotic ones.

Habitat structure and egg distributions in the processionary caterpillar Ochrogaster lunifer: lessons for conservation and pest management

1. The spatial and temporal distribution of eggs laid by herbivorous insects is a crucial component of herbivore population stability, as it influences overall mortality within the population. Thus an ecologist studying populations of an endangered butterfly can do little to increase its numbers through habitat management without knowledge of its egg-laying patterns across individual host-plants under different habitat management regimes. At the other end of the spectrum, a knowledge of egg-laying behaviour can do much to control pest outbreaks by disrupting egg distributions that lead to rapid population growth. 2. The distribution of egg batches of the processionary caterpillar Ochrogaster lunifer on acacia trees was monitored in 21 habitats during 2 years in coastal Australia. The presence of egg batches on acacias was affected by host-tree 'quality' (tree size and foliar chemistry that led to increased caterpillar survival) and host-tree 'apparency' (the amount of vegetation surrounding host-trees). 3. In open homogeneous habitats, more egg batches were laid on high-quality trees, increasing potential population growth. In diverse mixed-species habitats, more egg batches were laid on low-quality highly apparent trees, reducing population growth and so reducing the potential for unstable population dynamics. The aggregation of batches on small apparent trees in diverse habitats led to outbreaks on these trees year after year, even when population levels were low, while site-wide outbreaks were rare. 4. These results predict that diverse habitats with mixed plant species should increase insect aggregation and increase population stability. In contrast, in open disturbed habitats or in regular plantations, where egg batches are more evenly distributed across high-quality hosts, populations should be more unstable, with site-wide outbreaks and extinctions being more common. 5. Mixed planting should be used on habitat regeneration sites to increase the population stability of immigrating or reintroduced insect species. Mixed planting also increases the diversity of resources, leading to higher herbivore species richness. With regard to the conservation of single species, different practices of habitat management will need to be employed depending on whether a project is concerned with methods of rapidly increasing the abundance of an endangered insect or concerned with the maintenance of a stable, established insect population that is perhaps endemic to an area. Suggestions for habitat management in these different cases are discussed. 6. Finally, intercropping can be highly effective in reducing pest outbreaks, although the economic gains of reduced pest attack may be outweighed by reduced crop yields in mixed-crop systems.

The jasmonate pathway.

Plants are faced with many of the same problems as animals-a need for regulation of metabolic processes and reproduction and for defense against enemies. Jasmonates in plants serve key roles in gene and metabolic regulation, defense, responses to trauma, reproduction, and possibly communication. Some remarkable features of plant responses, such as production of repellent volatiles as a defense against herbivorous insects, or the massive transcriptional reprogramming that occurs in response to wounding, are under the control of the jasmonate pathway. Details of the jasmonate signaling pathway are currently at the center of active research that is generating exciting results. The Jasmonate Biochemical Pathway at the STKE Connections Maps is designed to present and keep pace with these developments.

Efeitos do sexo, do vigor e do tamanho da planta hospedeira sobre a distribuição de insetos indutores de galhas em Baccharis pseudomyriocephala Teodoro (Asteraceae)

Several hypotheses have been proposed to explain the patterns of host plant utilization by herbivorous insects in natural communities. We tested four hypotheses aiming to understand the pattern of attack by gall-inducing insects on the dioecious shrub, Baccharis pseudomyriocephala (Asteraceae). The shrub occurs in the Parque Estadual do Itacolomi, Southeastern Brazil, and supports ten species of galling insects. The following hypotheses were tested: i) male plants are more attacked by galling insects than female plants; ii) larger plant modules are preferentially attacked by galling insects; iii) galling insects perform better on larger modules than on smaller modules; iv) galling insects increase in abundance with meristematic availability. To address these questions, 240 plants (120 of each sex) were sampled in both reproductive and vegetative periods. We recorded the growth rate (4 cm), inflorescence and fruit production, attack rates of the galling insects, and their survivorship and mortality per shoot (module). Modules were separated into size classes (cm) and analyzed by regressions and ANCOVAs. Module size and reproductive effort were positively correlated with host plant size. We did not observe any effect of host plant gender on either variables. In the same way, host plant sex did not show any influence on the abundance and richness of galling insects. Although the abundance of galling insects showed a positive correlation with shoot size, the trend disappeared when the analyses were performed taking into consideration the number of galls per unit of growth (number of galls/cm of shoot) or biomass (number of galls/dry weight). Larval survivorship was not influenced by shoot size. Also, we observed that the abundance of one species of hemipteran galling insect showed a positive relation with leaf biomass. Therefore, we conclude that gender and vigor of this plant species do not influence the community structure of its galling herbivores.

Effects of sex, host-plant deprivation and presence of conspecific immatures on the cannibalistic behavior of wild Ascia monuste orseis (Godart) (Lepidoptera, Pieridae)

Effects of sex, host-plant deprivation and presence of conspecific immatures on the cannibalistic behavior of wild Ascia monuste orseis (Godart) (Lepidoptera, Pieridae). The specialist cabbage caterpillar Ascia monuste orseis (Lepidoptera, Pieridae) feeds on plants of the Brassicaceae family, but may eventually ingest conspecific eggs and larvae during the larval stage. The present study examines feeding behavior of 4th and 5th instar cabbage caterpillars in relation to sex, host-plant deprivation and presence of conspecifics. We recorded number of egg ingested per larvae, developmental indices and duration of feeding, exploratory and resting behavior. Kale deprived caterpillars presented high rates of cannibalism, development delay and decreased fecundity. Cannibalism rates were not influenced by the sex of the larvae. In general, the presence of conspecific eggs did not interfere with the frequency and duration of the categorical behavioral events. We conclude that food availability is a strong factor influencing the extent to which A. monuste orseis caterpillars cannibalize.

Perception, signaling and molecular basis of oviposition-mediated plant responses.

Eggs deposited on plants by herbivorous insects represent a threat as they develop into feeding larvae. Plants are not a passive substrate and have evolved sophisticated mechanisms to detect eggs and induce direct and indirect defenses. Recent years have seen exciting development in molecular aspects of egg-induced responses. Some egg-associated elicitors have been identified, and signaling pathways and egg-induced expression profiles are being uncovered. Depending on the mode of oviposition, both the jasmonic acid and salicylic acid pathways seem to play a role in the induction of defense responses. An emerging concept is that eggs are recognized like microbial pathogens and innate immune responses are triggered. In addition, some eggs contain elicitors that induce highly specific defenses in plants. Examples of egg-induced suppression of defense or, on the contrary, egg-induced resistance highlight the complexity of plant-egg interactions in an on-going arms race between herbivores and their hosts. A major challenge is to identify plant receptors for egg-associated elicitors, to assess the specificity of these elicitors and to identify molecular components that underlie various responses to oviposition.

Plant Immune Responses: Aphids Strike Back.

To survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses.

Plant Immune Responses: Aphids Strike Back.

To survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses.

Phytophagous insect fauna tracks host plant responses to exotic grass invasion

The high dependence of herbivorous insects on their host plants implies that plant invaders can affect these insects directly, by not providing a suitable habitat, or indirectly, by altering host plant availability. In this study, we sampled Asteraceae flower heads in cerrado remnants with varying levels of exotic grass invasion to evaluate whether invasive grasses have a direct effect on herbivore richness independent of the current disturbance level and host plant richness. By classifying herbivores according to the degree of host plant specialization, we also investigated whether invasive grasses reduce the uniqueness of the herbivorous assemblages. Herbivorous insect richness showed a unimodal relationship with invasive grass cover that was significantly explained only by way of the variation in host plant richness. The same result was found for polyphagous and oligophagous insects, but monophages showed a significant negative response to the intensity of the grass invasion that was independent of host plant richness. Our findings lend support to the hypothesis that the aggregate effect of invasive plants on herbivores tends to mirror the effects of invasive plants on host plants. In addition, exotic plants affect specialist insects differently from generalist insects; thus exotic plants affect not only the size but also the structural profile of herbivorous insect assemblages.

Prey captured and used in Polistes versicolor (Olivier) (Hymenoptera: Vespidae) Nourishment

As vespas sociais são predadoras de muitas espécies de insetos e o estudo de suas presas pode revelar seu potencial para programas de controle biológico de pragas. Foram realizadas 240h de coleta de presas em 32 colônias de Polistes versicolor (Olivier) no município de Juiz de Fora, MG, de março de 2000 a fevereiro de 2001. As presas capturadas por P. versicolor foram, principalmente, das ordens Lepidoptera (95,4%) e Coleoptera (1,1%) além de 3,4% de indivíduos não identificados. A espécie mais coletada foi Chlosyne lacinia saundersii Doubleday & Hewitson (13,5%) (Lepidoptera: Nymphalidae) e o número total estimado de presas capturadas por colônia de P. versicolor foi de 4.015 indivíduos por ano. Isso mostra que a espécie pode ser utilizada em programas de manejo integrado de pragas de insetos herbívoros, principalmente lagartas desfolhadoras.

Leaf trait variation on Erythroxylum tortuosum (Erythroxylaceae) and its relationship with oviposition preference and stress by a host-specific leaf miner

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Oviposition of a leaf-miner on Erythroxylum tortuosum (Erythroxylaceae) leaves: hierarchical variation of physical leaf traits

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)