Mariano P. Grilli

Regional abundance of a planthopper pest: the effect of host patch area and configuration

The effect of host patch area and configuration on the abundance of dispersing individuals of Delphacodes kuscheli Fennah (Homoptera: Delphacidae), the vector of Río Cuarto disease in maize, was investigated in the main maize production area of Argentina. Actively dispersing D. kuscheli individuals were collected from 15 sampling sites during the spring seasons of 1999 and 2000, using sticky traps placed at 6 m above ground level. Host patches were detected and quantified using Landsat 5 TM images for the periods studied. The spatial pattern analysis program FRAGSTATS was used to estimate the total class area, largest patch index, mean proximity index, and patch cohesion index for patches of winter pastures (the main insect host during winter) as observed from the satellite images. Landsat 5 TM estimations showed local variability in the proportion of winter pastures, with patches bigger during 1999 than during 2000, but these patches represented only a very small part of the total landscape. Proximity between host patches was also variable between sites and higher values of cohesion occurred during the first sampling season. The relationship between host area and D. kuscheli mean abundance was adjusted to an exponential (R2= 77.5%) model. Host patch dominance, host patch isolation, and host patch connectivity all showed a positive relationship with D. kuscheli mean abundance, adjusting significantly to linear models (R2= 92%, R2= 90%, and R2= 22%, respectively). Outbreaks of Río Cuarto disease in the main maize production area of Argentina are related to high vector populations. The results indicate that the abundance of D. kuscheli depends on factors related to the abundance and configuration of its host patches.

Spatial synchrony of planthopper species with contrasting outbreak behaviour

1 We studied the synchrony of two sympatric delphacids species with different outbreak behaviours over a range of 250 km in Argentina.

Effect of Local Land Use on Populations of a Disease Vector Planthopper

Abstract Delphacodes kuscheli (Hemiptera: Delphacidae) is the vector of maize rough dwarf virus that affects maize production in the central region of Argentina. The spatial abundance pattern and body morphology of the insect vector were studied during the spring and summer of 1999 and 2000 in endemic and nonendemic areas affected by this virus. An estimation of insect density was obtained from high sticky traps (6 m high) placed at nine sampling sites along a 500-km transect that crossed the main maize production area in Argentina. Host patches were detected, and their areas were measured using Landsat 5 Thematic Mapper (TM) imagery from the region to be studied. Population phenology of the individuals collected in the sampling sites was compared using multivariate analysis of morphometric variables. The land use estimated from Landsat 5 TM images varied according to the different sites and years. Areas with similar proportion of winter pastures, winter cereals, and perennial pastures were grouped together by complete linkage cluster analysis. The mean abundance of the vector varied and did not show a consistent pattern. The highest abundances were not found in the traps placed in the endemic region. Multiple linear regression of the proportion of area (arcsine transformed) covered by annual pastures, perennial pastures, and winter crops versus mean abundance of D. kuscheli (expressed as insect/trap/d) were significant for both years (R2 = 0.91 for 1999 and R2 = 0.82 for 2000). The function that related insect abundance and host area was different each year; this suggested that other factors were affecting the “insect productivity” of a certain host area. There were clear morphometric differences among the individuals collected in the different sampling sites, although the sites were not so far away from one another (50 km). When comparing the phenotypes of the insects collected in different sites, 55 (1999) and 51% (2000) of the cases were correctly assigned to the sites from which the individuals were collected. These percentages increased to 74 and 62% if the individuals were grouped according to the cluster of land use obtained from Landsat 5 TM images. In all cases, Wilk’s lambdas were highly significant. The role of the distribution, abundance, and quality of the host plants is analyzed in this study.

Boll weevil invasion process in Argentina

The boll weevil, Anthonomus grandis grandis Boheman, is the most destructive cotton pest in the Western Hemisphere. In 1993, the pest was reported in Argentina, and in 1994 boll weevils were captured in cotton fields in Formosa Province on the border between Argentina and Paraguay. The pest has subsequently moved to new areas, and in 2006 it was reported in Argentina’s main cotton growing region. This study describes the first stage of the boll weevil invasion into areas of Argentina using a network of pheromone traps from 1997 to 2000 in Pilcomayo and Pilagás departments. A temporal autocorrelation analysis of the numbers of collected boll weevils in seven localities, and a synchrony analysis of 70 rural settlements for the 1997–2000 period, were the approaches we used to characterize boll weevil dispersal and establishment. Total abundances of boll weevils varied but a positive correlation between total number of individuals captured and the number of traps that captured them was detected. While short term temporal autocorrelation was observed, spatial synchrony was not found. The role of alternative hosts in facilitating the advance of boll weevils into Argentina is discussed.

Relationships between land-use types and plant species used by traditional ethno-medical system.

Aims: The agricultural frontier advances progressively on forested regions in Central Argentina, changing the landscape structure by extremely reducing the extension of native forests. In rural communities that are related to the forests, it is possible that severe changes in the landscapes can have an impact on the knowledge and uses of medicinal plants. The aim of this paper was to evidence some general patterns between the ethnobotanical information recorded in the Chaco region and some characteristics of the landscape. Specifically, we hypothesized that the knowledge on medicinal plants and their type (native or exotic) are related to different types of land use (i.e. different proportions of native forests). Place and Duration of Study: The study was performed 15 rural localities within the Chaco phytogeographic regionin Cordoba, Argentina, conducted between 2004 and 2012. Methodology: A total of 279 interviews were conducted. Plant species were identified according to their status (native or exotic), and a standardized proportion of exotic Original Research Article European Journal of Medicinal Plants, 4(9): 998-1021, 2014 999 species was calculated for each site. The different types of land use and their proportions were estimated in 15 rural localities using satellite images. A Principal Component Analysis and a bivariate Spearman correlation were performed to analyze the associations among land-use types, the proportion of native forests and the knowledge of medicinal plants. Results: In general, people had known many native and exotic medicinal plants. Nevertheless, in those localities where landscapes have experienced higher deforestation rates, exotic medicinal plants are more available than native ones (cultivated in gardens and orchards). The tradition of maintaining exotic species in gardens may contribute to maintain the ethno-medical systems in regions of severe forest fragmentation. Conclusion: The disappearance of the forest showed a positive association with losses in the knowledge and use of native medicinal plants.

The role of host patch characteristics and dispersal capability in distribution and abundance of Arhopalus rusticus in central Argentina

Host patch characteristics may influence the abundance of a species, but this will depend on the species’ dispersal ability and the distance between suitable patches. In central Argentina, an area of introduced pine forest was planted for wood production in the 1940s. In 2006, an invading longhorn beetle, Arhopalus rusticus (L.) (Coleoptera: Cerambycidae), was detected in the area. Since then, the species has expanded its range until it occupies the whole area. We analyze how the configuration of host patches and flight performance of A. rusticus affect its distribution. The study was performed in the center‐west of Córdoba Province, Argentina, with 24 000 ha of introduced pine forests the main pine production zone of the province. Land cover was estimated using Landsat 8 scenes. Landscape was quantified by estimating the focal patchs area, fractal dimension index (FRAC), and Euclidean nearest neighbor distance (ENN). Focal patch area showed a positive relationship with A. rusticus abundance, whereas ENN and FRAC had a negative relationship. The dispersal ability of A. rusticus was determined by putting recently emerged individuals to fly in flight mills. The flight performance results indicated that the species was probably introduced in the area by human activity, then rapidly established and expanded to the whole area. This indicates the importance of preventing its arrival in other pine production areas of Argentina, as it has proved to be an extremely successful invader.