Diversidad de enemigos naturales de pulgones en cultivos de lechuga

Este trabajo ha sido subvencionado por la beca predoctoral del Ministerio de Ciencia y Tecnología: AGL2003-0753-C03-01 y forma parte de la Tesis Doctoral de I. Morales (BES-2004-5217)

Life Table and Population Parameters of Nasonovia ribisnigri (Homoptera: Aphididae) at different Constant Temperatures

Age-specific life tables of the lettuce aphid, Nasonovia ribisnigri (Mosley), feeding on lettuce were determined at different constant temperatures under controlled conditions. Our results showed that the proportion of alates increased with increasing temperatures, remaining below 7% at 16°C and increasing to 40–57% at a temperature above 20°C. The longest developmental time of apterous aphids was obtained at 8°C (31.5 d), and the shortest was at 26°C (6.2 d), whereas the developmental time of alates was always 0.7–1.1 d longer than for apterous. Most aphids needed four instars to reach adult stage, but at 8, 26, and 28°C, many individuals passed through five or six molts. Age-specific survivorship (lx) was always above 90% at the temperature range of 16–24°C. Mortality rate (qx) was rather low but constant at 8°C. However, mortality was high at 28°C and occurred mainly in the last nymphal instars and adult stage. Unexpectedly, no nymphs were produced by the adult morphs at 28°C, but effective fecundity was high at 8°C. Fecundity for alates was always lower than for the apterous aphids at the same temperature. The largest intrinsic rate of natural increase (rm), and the mean relative growth rate () occurred at 24°C, for both apterous and alate morphs, and the lowest at 8°C. Our results show that lettuce aphid is better adapted to survive and reproduce at low (8°C) than at high (28°C) temperatures, and its best performance occurred at 20–24°C.We thank E. Garzo for technical advise. This work was supported by the Comisión Interministerial de Ciencia y Tecnología (AGL-2003-0753-C03-01).Peer reviewe

Pathogenicity of hyphomycetous fungi against Cyclocephala signaticollis

8 pages, and tables.Susceptibility of the white grub Cyclocephala signaticollis Burmeister (Coleoptera: Scarabaeidae: Dynastinae) larvae to seven isolates of Beauveria bassiana (Balsamo) Vuillemin, five of Metarhizium anisopliae (Metschnikoff) Sorokin and two of Paecilomyces lilacinus (Thom) Samson (Deuteromycotina: Hyphomycetes) was investigated. Among 14 fungal isolates screened the most virulent was a B. bassiana isolate (Bb 53) that caused 70% mortality of third instar larvae in 40 days after inoculation at 1 · 108 conida/ml. Strains of M. anisopliae and P. lilacinus showed low efficacy or no virulence to the target host.Peer reviewe

Impacto de cubiertas agrotextiles en el control de pulgones, mosca blanca y virus en cultivos de lechuga y bróculi

14 páginas, tablas estadísticas.En el presente trabajo se ha evaluado durante 2 años consecutivos el grado de eficacia de cubiertas agrotextiles en el control de mosca blanca, pulgones y virus en cultivos de lechuga y bróculi en la Comunidad de Madrid y Navarra, respectivamente. También se ha estudiado su efecto sobre el rendimiento y valor comercial del cultivo. Los resultados indican que este tipo de cubiertas puede producir un efecto beneficioso en el cultivo durante el periodo más frío del año (final del otoño al inicio de primavera), reduciendo en algunos casos el daño cosmético producido tanto por pulgones como por mosca blanca. Sin embargo, en caso de no ser retiradas a tiempo, los efectos de las cubiertas pueden ser negativos en cultivos de lechuga, debido a una inducción prematura de floración y reducción del peso por planta.Peer reviewe

Interplant movement and spatial distribution of alate and apterous morphs of Nasonovia ribisnigri (Homoptera: Aphididae) on lettuce

9 páginas, 3 tablas y 3 figurasKnowledge on colonization modes and interplant movement of Nasonovia ribisnigri can contribute to the development of optimal control of this pest. The aim of this study was to determine the spatio-temporal distribution and the mode of spread between adult morphs of Nasonovia ribisnigri, comparing spring and autumn lettuce protected crops. The spatial and temporal pattern was analyzed using the spatial analysis by distance indices (SADIE) methodology and other related displacement indices. The population size of N. ribisnigri was greater in the autumn than in the spring growing seasons due to milder temperatures. The percentage of plants colonized by aphids was higher in spring than in autumn, showing the great dispersal potential of this aphid species independent of their population size. Differential propensity for initial displacement from the central plant was observed between adult morphs in spring, resulting in a greater ability of apterous han alate aphids to spread far away from the source plant. In autumn, both adult morphs showed an initial reduced displacement; however, the number of plants infested (&20%) with at least one aphid at this initial time (seven days) was similar for both adult morphs and both growing seasons. Analysis of the spatial pattern of both adult morphs revealed a predominantly random distribution for both spring and autumn trials. This pattern was achieved by a prevalent random movement over the area (γ&0.5). These results highlight the ability of the apterous N. ribisnigri to spread within greenhouse lettuce crops early in the spring, suggesting that detection of the pest by deep visual inspection is required after lettuce emergence.This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT N°AGL-2003-0753-C03-01).Peer reviewe

Avances hacia el Control Integrado de pulgones en lechuga

6 páginas, 6 fotos.En este trabajo se expone un compendio de resultados procedentes de varios años de estudio sobre la dinámica poblacional de pulgones de lechuga su incidencia como vectores de virus y sobre diferentes métodos alternativos para su control. Se destacan los avances alcanzados en el uso de barreras físicas con agrotextiles y materiales fotoselectivos. Tambien se describe los parasitoides, depredadores y hongos entomopatógenos asociados a pulgones en cultivo de lechuga en la zona Centro de la Península Ibérica y se identificaron especies vegetales candidatas para fomentar el control biológico por conservacion.Este trabajo fue financiado en el marco de los proyectos del Plan Nacional de I+D+I, AGL-2000- 2006, AGL-2003-07532-C03, AGL-2005-01449/ AGR, AGL2007-66399-C03-02/AGR).Peer reviewe

The spatio-temporal relationships among aphids, the entomophthoran fungus, Pandora neoaphidis, and aphidophagous hoverflies in outdoor lettuce

8 páginas, figuras y tablas estadísticas.Worldwide, aphids are the key pests of lettuce, and they coexist with natural enemies in different guilds. In our study, the spatio-temporal patterns of aphids colonizing lettuce were assessed and compared with the distribution of an entomopathogenic fungus and hoverfly larvae during two spring lettuce growing seasons. Counts of aphid density, entomopathogenic fungal-infected aphids and hoverfly larvae present on lettuce plants were recorded and their spatial distribution analyzed using the Spatial Analysis by Distance IndicEs (SADIE) method to determine aggregation and association indices. Three aphid species (Nasonovia ribisnigri, Macrosiphum euphorbiae and Acyrtosiphon lactucae) colonize lettuce plants in early spring; however, their natural enemies arrive several weeks later. Pandora neoaphidis was the only fungus identified to cause aphid mortality, and Sphaerophoria scripta was the most abundant syrphid species preying on lettuce aphids. In both 2007 and 2008, the aphids followed ephemeral spatio-temporal dynamics at the field scale. The maximum aphid aggregation was concurrent with the highest aphid density and with the complete development of the rosette lettuce leaf-stage. P. neoaphidis-infected aphids showed more aggregation over time than hoverfly larvae. The maximum spatial structure was recorded for both natural enemy species close to the harvest date and at the time when the aphid populations were distributed at random. Significant spatial associations between P. neoaphidis and hoverfly larvae were only detected close to the time of harvest, which reduces the risk of intraguild predation between these two natural enemies of aphids at the field scale.was financially supported by Contract No. I3P-PC2006-1 from the ‘‘Programa de Incorporación de Investigadores” CSIC-FSE. This work was funded by the Spanish Ministry of Science and Education (Research Grants AGL-2005-01449/AGR).Peer reviewe

Temporal and spatial spread of Lettuce mosaic virus in lettuce crops in central Spain: factors involved in Lettuce mosaic virus epidemics

Lettuce mosaic virus (LMV) is transmitted by aphid vectors in a nonpersistent manner as well as by seeds. The virus causes severe disease outbreaks in commercial lettuce crops in several regions of Spain. The temporal and spatial patterns of spread of LMV were studied in autumn 2002 in the central region of Spain. Symptomatic lettuce (var. Cazorla) plant samples were collected weekly, first at the seedling stage from the greenhouse nursery and later outdoors after transplantation. The exact position of symptomatic plants sampled in the field was recorded and then material was tested by enzyme-linked immunosorbent assay to assess virus infection. Cumulative spatial data for infected plants at different growth stages were analysed using spatial analysis by distance indices. For temporal analysis, the monomolecular, Gompertz, logistic and exponential models were evaluated for goodness of fit to the entire set of disease progress data obtained. The results indicated that the disease progress curve of LMV epidemics in the selected area is best described by a Gompertz model and that the epidemic follows a polycyclic disease progression. Our data suggest that secondary cycle of spread occurs when noncolonising aphid species land on the primary infected plants (probably coming from infected seed) and move to adjacent plants before leaving the crop. The role of weeds growing close to lettuce fields as potential inoculum sources of virus and the aphid species most likely involved in the transmission of LMV were also identifiedThis work was supported by the Spanish Ministry of Education and Science (Plan National grants nos AGL-2000-2006 and AGL-2003-07532-C03-01).Peer reviewe

Diversidad de enemigos naturales de pulgones en cultivos de lechuga

6 páginas, fotos.El uso masivo de insecticidas dirigidos a aumentar los rendimientos de producción, produce una serie de efectos secundarios muy perjudiciales para el medio ambiente, como son la contaminación de las aguas y de los suelos, los residuos en los alimentos, la potenciación de plagas secundarias, la aparición de resistencias a dichos insecticidas y la eliminación de polinizadores y fauna autóctonaPeer reviewe

Principales agentes de biocontrol en cultivos de lechuga en la zona centro de España

4 páginas, 5 fotos y una tabla estadística.En este trabajo se han identificado las principales especies de enemigos naturales de pulgones presentes en los cultivos de lechuga de la zona centro de la Península IbéricaPeer reviewe