Natural habitat connectivity and organic management modulate pest dispersal, gene flow, and natural enemy communities.

The simplification and fragmentation of agricultural landscapes generate effects on insects at multiple spatial scales. As each functional group perceives and uses the habitat differently, the response of pest insects and their associated natural enemies to environmental changes varies. Therefore, landscape structure may have consequences on gene flow among pest populations in space. This study aimed to evaluate the effects of local and landscape factors, at multiple scales, on the local infestation, gene flow and broad dispersion dynamics of the pest insect Bemisia tabaci (Genn.) Middle East-Asia Minor 1 (MEAM-1, former biotype B) (Hemiptera: Aleyrodidae) and its associated natural enemies in a tropical agroecosystem. We evaluated the abundance of B. tabaci populations and their natural enemy community in 20 tomato farms in Brazil and the gene flow between farms from 2019 to 2021. Landscapes dominated by agriculture resulted in larger B. tabaci populations and higher gene flow, especially in conventional farms. A higher density of native vegetation patches disfavored pest populations, regardless of the management system. The results revealed that whitefly responds to intermediate spatial scales and that landscape factors interact with management systems to modulate whitefly populations on focal farms. Conversely, whitefly natural enemies benefited from higher amounts of natural vegetation at small spatial scales, while the connectivity between natural habitat patches was beneficial for natural enemies regardless of the distance from the focal farm. The resulting dispersion model predicts that the movement of whiteflies between farms increases as the amount of natural vegetation decreases. Our findings demonstrate that landscape features, notably landscape configuration, can mediate infestation episodes, as they affect pest insects and natural enemies in opposite ways. We also showed that landscape features interact with farm traits, which highlights the need for management strategies at multiple spatial scales. In conclusion, we demonstrated the importance of the conservation of natural areas as a key strategy for area-wide ecological pest management and the relevance of organic farming to benefit natural enemy communities in tropical agroecosystems.

Naturally fragmented and isolated distribution in subtropical grassland patches affects genetic diversity and structure at different spatial scales: The case of Tibouchina hatschbachii, an endemic shrub from Brazil.

PREMISE OF THE STUDY: The genetic structure of organisms results from the interactions between life history traits and the ecological and demographic characteristics of the landscape that shape the intra- and interpopulation genetic variation in space and time. In this study, we used a species restricted to islands of grassland vegetation in southern Brazil to investigate the effects of its naturally fragmented distribution on diversity and genetic structure patterns. METHODS: Diversity and intra- and interpopulational genetic structure were analyzed using polymorphisms of eight nuclear microsatellite markers in 205 individuals of T. hatschbachii and Bayesian and multivariate methods. KEY RESULTS: At the intrapopulation level, populations presented low genetic diversity and strong spatial genetic structure, indicating a greater spatial autocorrelation until ∼50-500 m. At the interpopulation level, genetic variation partitioned into two geographically structured genetic clusters. Gene flow through pollen was more efficient than gene flow by seeds. CONCLUSIONS: Genetic structure was influenced locally by seed and pollen dispersal dynamics and regionally by fragmentation of the grassland landscape. This study highlights the importance of geological barriers, and potentially a role for genetic drift, in influencing diversification of species in subtropical grasslands of southern Brazil.

Differentially expressed genes and proteins upon drought acclimation in tolerant and sensitive genotypes of Coffea canephora.

The aim of this study was to investigate the molecular mechanisms underlying drought acclimation in coffee plants by the identification of candidate genes (CGs) using different approaches. The first approach used the data generated during the Brazilian Coffee expressed sequence tag (EST) project to select 13 CGs by an in silico analysis (electronic northern). The second approach was based on screening macroarrays spotted with plasmid DNA (coffee ESTs) with separate hybridizations using leaf cDNA probes from drought-tolerant and susceptible clones of Coffea canephora var. Conilon, grown under different water regimes. This allowed the isolation of seven additional CGs. The third approach used two-dimensional gel electrophoresis to identify proteins displaying differential accumulation in leaves of drought-tolerant and susceptible clones of C. canephora. Six of them were characterized by MALDI-TOF-MS/MS (matrix-assisted laser desorption-time of flight-tandem mass spectrometry) and the corresponding proteins were identified. Finally, additional CGs were selected from the literature, and quantitative real-time polymerase chain reaction (qPCR) was performed to analyse the expression of all identified CGs. Altogether, >40 genes presenting differential gene expression during drought acclimation were identified, some of them showing different expression profiles between drought-tolerant and susceptible clones. Based on the obtained results, it can be concluded that factors involved a complex network of responses probably involving the abscisic signalling pathway and nitric oxide are major molecular determinants that might explain the better efficiency in controlling stomata closure and transpiration displayed by drought-tolerant clones of C. canephora.