Insetos predadores de sementes e suas relações com a qualidade e a morfologia de frutos e sementes

Pós-graduação em Ciências Biológicas (Botânica) - IBB

Contributions of demography and dispersal parameters to the spatial spread of a stage-structured insect invasion

Stage-structured models that integrate demography and dispersal can be used to identify points in the life cycle with large effects on rates of population spatial spread, information that is vital in the development of containment strategies for invasive species. Current challenges in the application of these tools include: (1) accounting for large uncertainty in model parameters, which may violate assumptions of ‘‘local’’ perturbation metrics such as sensitivities and elasticities, and (2) forecasting not only asymptotic rates of spatial spread, as is usually done, but also transient spatial dynamics in the early stages of invasion. We developed an invasion model for the Diaprepes root weevil (DRW; Diaprepes abbreviatus [Coleoptera: Curculionidae]), a generalist herbivore that has invaded citrus-growing regions of the United States. We synthesized data on DRW demography and dispersal and generated predictions for asymptotic and transient peak invasion speeds, accounting for parameter uncertainty. We quantified the contributions of each parameter toward invasion speed using a ‘‘global’’ perturbation analysis, and we contrasted parameter contributions during the transient and asymptotic phases. We found that the asymptotic invasion speed was 0.02–0.028 km/week, although the transient peak invasion speed (0.03– 0.045 km/week) was significantly greater. Both asymptotic and transient invasions speeds were most responsive to weevil dispersal distances. However, demographic parameters that had large effects on asymptotic speed (e.g., survival of early-instar larvae) had little effect on transient speed. Comparison of the global analysis with lower-level elasticities indicated that local perturbation analysis would have generated unreliable predictions for the responsiveness of invasion speed to underlying parameters. Observed range expansion in southern Florida (1992–2006) was significantly lower than the invasion speed predicted by the model. Possible causes of this mismatch include overestimation of dispersal distances, demographic rates, and spatiotemporal variation in parameter values. This study demonstrates that, when parameter uncertainty is large, as is often the case, global perturbation analyses are needed to identify which points in the life cycle should be targets of management. Our results also suggest that effective strategies for reducing spread during the asymptotic phase may have little effect during the transient phase. Includes Appendix.

Genetic Variability of Beauveria bassiana and a DNA Marker for Environmental Monitoring of a Highly Virulent Isolate Against Cosmopolites sordidus

The banana weevil Cosmopolites sordidus (Germar) is one of a number of pests that attack banana crops. The use of the entomopathogenic fungus Beauveria bassiana as a biological control agent for this pest may contribute towards reducing the application of chemical insecticides on banana crops. In this study, the genetic variability of a collection of Brazilian isolates of B. bassiana was evaluated. Samples were obtained from various geographic regions of Brazil, and from different hosts of the Curculionidae family. Based on the DNA fingerprints generated by RAPD and AFLP, we found that 92 and 88 % of the loci were polymorphic, respectively. The B. bassiana isolates were attributed to two genotypic clusters based on the RAPD data, and to three genotypic clusters, when analyzed with AFLP. The nucleotide sequences of nuclear ribosomal DNA intergenic spacers confirmed that all isolates are in fact B. bassiana. Analysis of molecular variance showed that variability among the isolates was not correlated with geographic origin or hosts. A RAPD-specific marker for isolate CG 1024, which is highly virulent to C. sordidus, was cloned and sequenced. Based on the sequences obtained, specific PCR primers BbasCG1024F (5'-TGC GGC TGA GGA GGA CT-3') and BbasCG1024R (5'-TGC GGC TGA GTG TAG AAC-3') were designed for detecting and monitoring this isolate in the field.

Electrophysiological Responses of the Naupactus bipes Beetle to Essential Oils from Piperaceae Species

Electrophysiological responses based on electroantennographic detection (GC-EAD) and electroantennography (EAG) analysis of Naupactus bipes beetles (Germar, 1824) (Coleoptera: Curculionidae: Brachycerinae) were used to test volatile oils of Piper gaudichaudianum, P. regnellii and P. hispidum. In the EAG experiments, female and male beetles showed significant EAG response to the three volatile oils of Piper species, with the females' responses slightly higher than the males'. The experiments with GC-EAD revealed that some terpenoids (namely, alpha-pinene, beta-pinene, myrcene, alpha-copaene and germacrene) present in the leaf essential oils of the Piper species are perceptible to female and male beetles.

Dispersal strategies of Aceria guerreronis (Acari: Eriophyidae), a coconut pest

The dispersal of plant-feeding mites can occur involuntarily, through transportation of infested plant parts, or voluntarily, by walking to new plant parts or to suitable spots where biotic (phoresis) or abiotic (wind, agricultural tools, etc.) factors carry them over long distances. Elucidating the dispersal mechanisms of the coconut mite, Aceria guerreronis Keifer, is important for understanding the process of colonization of new fruits of a same or different plants, essential for the improvement of control strategies of this serious coconut pest. Thus, the objective of this work was to investigate the voluntary dispersal mechanisms of this mite. The hypothesis that the coconut mite disperses by walking, phoresis or wind were tested. The coconut mite was shown to be able to walk short distances between fruits of the same bunch or between bunches of the same plant. Phoresis on insects of the orders Hymenoptera (Apidae), Coleoptera (Curculionidae) and Lepidoptera (Phycitidae) was evaluated in the laboratory and in the field. Although in the laboratory mites were shown to be able to climb onto honeybees, field investigations failed to show these insects as important carriers of the pest, corroborating findings of previous works; however, both laboratory and field investigations suggested the curculionid Parisoschoenus obesulus Casey to be able to transport the coconut mite between plants. Similarly, laboratory and field investigations suggested wind to be important in the dispersal of the coconut mite between plants.

Patterns of functional enzyme activity in fungus farming ambrosia beetles

Introduction In wood-dwelling fungus-farming weevils, the so-called ambrosia beetles (Curculionidae: Scolytinae and Platypodinae), wood in the excavated tunnels is used as a medium for cultivating fungi by the combined action of digging larvae (which create more space for the fungi to grow) and of adults sowing and pruning the fungus. The beetles are obligately dependent on the fungus that provides essential vitamins, amino acids and sterols. However, to what extent microbial enzymes support fungus farming in ambrosia beetles is unknown. Here we measure (i) 13 plant cell-wall degrading enzymes in the fungus garden microbial consortium of the ambrosia beetle Xyleborinus saxesenii, including its primary fungal symbionts, in three compartments of laboratory maintained nests, at different time points after gallery foundation and (ii) four specific enzymes that may be either insect or microbially derived in X. saxesenii adult and larval individuals. Results We discovered that the activity of cellulases in ambrosia fungus gardens is relatively small compared to the activities of other cellulolytic enzymes. Enzyme activity in all compartments of the garden was mainly directed towards hemicellulose carbohydrates such as xylan, glucomannan and callose. Hemicellulolytic enzyme activity within the brood chamber increased with gallery age, whereas irrespective of the age of the gallery, the highest overall enzyme activity were detected in the gallery dump material expelled by the beetles. Interestingly endo-β-1,3(4)-glucanase activity capable of callose degradation was identified in whole-body extracts of both larvae and adult X. saxesenii, whereas endo-β-1,4-xylanase activity was exclusively detected in larvae. Conclusion Similar to closely related fungi associated with bark beetles in phloem, the microbial symbionts of ambrosia beetles hardly degrade cellulose. Instead, their enzyme activity is directed mainly towards comparatively more easily accessible hemicellulose components of the ray-parenchyma cells in the wood xylem. Furthermore, the detection of xylanolytic enzymes exclusively in larvae (which feed on fungus colonized wood) and not in adults (which feed only on fungi) indicates that only larvae (pre-) digest plant cell wall structures. This implies that in X. saxesenii and likely also in many other ambrosia beetles, adults and larvae do not compete for the same food within their nests - in contrast, larvae increase colony fitness by facilitating enzymatic wood degradation and fungus cultivation.

Relevamiento de plagas y enemigos naturales en el cultivo de lechuga : : provincia de La Pampa (Argentina)

En la provincia de La Pampa son escasos los datos sobre relevamiento de plagas y de especies benéficas en lechuga, por ello resulta necesario conocer e investigar los organismos perjudiciales y sus enemigos naturales y las condiciones predisponentes al incremento de sus poblaciones. Los objetivos de este trabajo fueron determinar las especies fitófagas para dos variedades de lechuga, en dos sistemas de producción, e identificar las especies benéficas que puedan actuar como controladores biológicos. El estudio se realizó en la huerta de la Facultad de Agronomía de la UNLPam, con muestreos semanales, desde julio hasta octubre de 2004, a campo con riego complementario y bajo cubierta en macrotúnel con riego por goteo, con las variedades de lechuga Grand Rapid y Gallega de Invierno. En cada variedad y en cada sistema se revisaron 6 plantas al azar, registrándose: especie, número de individuos y su estado de desarrollo. Se comparó mediante ANOVA y test de Tukey (a = 0,05). Se detectó la presencia de dos especies de pulgones: Myzus persicae Sulzer (Homoptera: Aphididae) y Nasonovia ribisnigri (Mosley) (primera cita de N. ribisnigri para la provincia de La Pampa). El mayor número de pulgones se concentró en el cultivo protegido bajo cubierta. Se registraron dos enemigos naturales de los pulgones: un hongo entomopatógeno y un parasitoide: Aphidius ervi (Hymenoptera: Braconidae). También se encontraron, en bajas densidades, larvas de Naupactus leucoloma Boheman (Coleoptera: Curculionidae) que se alimentaban de las hojas.

Evaluación de aceites y extractos vegetales para el control de Sitophilus zeamaiz y su efecto en la calidad de semilla de maíz

Sitophilus zeamaiz es una de las especies de gorgojos que más pérdidas causa en granos almacenados en el mundo; su control se basa principalmente en productos sintéticos, que con el paso del tiempo resultan menos efectivos. En la presente investigación se evaluaron aceites vegetales de ricino, soya y extractos vegetales de neem y lila sobre poblaciones de S. zeamaiz y sus efectos sobre la germinación y parámetros fisiológicos de las plántulas. Los resultados muestran que el aceite de soya dio los mejores resultados de control, al presentar mortalidades entre un 92 y 100% a las 192 horas. Sin embargo, este aceite afecta la germinación a dosis de 2000 a 10000 ppm. El extracto de neem presentó mortalidades del 78,75 y 91,25% a las 192 horas, sin afectar la germinación ni las propiedades agronómicas. Finalmente, el aceite de ricino y el extracto de lila fueron los tratamientos que, para las condiciones del presente estudio, no mostraron altas mortalidades sobre S. zeamaiz.

Macroinvertebrate abundance and proportion of trait categories in river biotopes across England and Wales

There is a long tradition of river monitoring using macroinvertebrate communities to assess environmental quality in Europe. A promising alternative is the use of species life-history traits. Both methods, however, have relied on the time-consuming identification of taxa. River biotopes, 1-100 m**2 'habitats' with associated species assemblages, have long been seen as a useful and meaningful way of linking the ecology of macroinvertebrates and river hydro-morphology and can be used to assess hydro-morphological degradation in rivers. Taxonomic differences, however, between different rivers had prevented a general test of this concept until now. The species trait approach may overcome this obstacle across broad geographical areas, using biotopes as the hydro-morphological units which have characteristic species trait assemblages. We collected macroinvertebrate data from 512 discrete patches, comprising 13 river biotopes, from seven rivers in England and Wales. The aim was to test whether river biotopes were better predictors of macroinvertebrate trait profiles than taxonomic composition (genera, families, orders) in rivers, independently of the phylogenetic effects and catchment scale characteristics (i.e. hydrology, geography and land cover). We also tested whether species richness and diversity were better related to biotopes than to rivers. River biotopes explained 40% of the variance in macroinvertebrate trait profiles across the rivers, largely independently of catchment characteristics. There was a strong phylogenetic signature, however. River biotopes were about 50% better at predicting macroinvertebrate trait profiles than taxonomic composition across rivers, no matter which taxonomic resolution was used. River biotopes were better than river identity at explaining the variability in taxonomic richness and diversity (40% and <=10%, respectively). Detailed trait-biotope associations agreed with independent a priori predictions relating trait categories to near river bed flows. Hence, species traits provided a much needed mechanistic understanding and predictive ability across a broad geographical area. We show that integration of the multiple biological trait approach with river biotopes at the interface between ecology and hydro-morphology provides a wealth of new information and potential applications for river science and management.

Determination of ages and fossil Coleoptera fauna from eight sites in the London region

These data sets report the fossil beetle assemblages identified from the Mesolithic to Late Bronze Age at eight sites in the London region. All but one of the study sites are within 2 km of the modern course of the Thames. The sites produced 128 faunal assemblages that yielded 218 identified species in 41 families of Coleoptera (beetles).  Beetle faunas of Mesolithic age indicate extensive wetlands near the Thames, bordered by rich deciduous woodlands. The proportion of woodland species declined in the Neolithic, apparently because of the expansion of wetlands, rather than because of human activities. The Early Bronze Age faunas contained a greater proportion of coniferous woodland and aquatic (standing water) species. An increase in the dung beetle fauna indicates the presence of sheep, cattle and horses, and various beetles associated with crop lands demonstrate the local rise of agriculture, albeit several centuries after the beginnings of farming in other regions of Britain. Late Bronze Age faunas show the continued development of agriculture and animal husbandry along the lower Thames. About 33% of the total identified beetle fauna from the London area sites have limited modern distributions or are extinct in the U.K. Some of these species are associated with the dead wood found in primeval forests; others are wetland species whose habitat has been severely reduced in recent centuries. The third group is stream-dwelling beetles that require clean, clear waters and river bottoms.