Abstract The corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), transmits three important plant pathogens that adversely affect corn crop and ranges from the USA to Argentina. The vector has a rich natural enemy complex that generates high levels of parasitism, but its populations are persistent and prevalent. We characterized the oviposition sites of D. maidis on young corn plants in order to verify the hypothesis that the vector has an oviposition strategy for mitigating parasitism. Oviposition locations on plants were assessed in the laboratory and eggs within corn plants were exposed to natural parasitism in a cornfield. Eggs were located mostly laid in the unfolded leaves and were attacked by five parasitoid species. Parasitism was significantly affected by the class of leaf and the position of the egg in the leaf. Anagrus virlai Triapitsyn was the most abundant parasitoid species, which emerged significantly higher in the basal blade than other species. Our results suggest that leafhoppers minimize egg parasitism by laying their eggs within concealed locations on the plant.

Soybean is a strategic crop for the economy of several South American countries. Phytophagous Lepidoptera are an important taxon affecting crop yield, being Anticarsia gemmatalis (Hübner) (Erebidae: Eulepidotinae), Rachiplusia nu (Guenée) and Chrysodeixis includens (Walker) (Noctuidae: Plusiinae) their main pests in Subtropical region of south America. The objectives of this study were to determine the location in field of eggs of Lepidoptera Noctuids in different organs of the soybean plant and its abundance and distribution in the plants considering the growth stage of the crop. Samples were taken weekly during three crop seasons, on a plot of 80 ha of soybean managed with conventional farming practices. The identification of lepidopteran eggs was performed following specific keys. More than 90% of eggs of the three defoliating species are deposited in the folioles, and especially in those located on the middle and upper level of the plants. Throughout the development of the crop, the highest densities of eggs were recorded in early stages (vegetative and flowering) being less abundant at fruiting. The study of the egg distribution of these pest species at the plant provides necessary information to establish preventive strategies for their control.

La soja es un cultivo estratégico en la economía de varios países sudamericanos. Las larvas de lepidópteros afectan el rendimiento del cultivo siendo Anticarsia gemmatalis (Hübner) (Erebidae: Eulepidotinae), Rachiplusia nu (Guenée) y Chrysodeixis includens (Walker) (Noctuidae: Plusiinae) las principales plagas en el área subtropical de Sudamérica. El objetivo del estudio fue determinar, a partir de muestras de campo, la ubicación de huevos de lepidópteros noctuoideos en los diferentes órganos de la planta de soja, así como su abundancia y distribución considerando el estado fenológico. Se realizaron muestreos semanales, durante tres campañas, en una parcela de 80 ha de soja manejadas con prácticas agrícolas convencionales. La identificación de los huevos de lepidópteros se realizó siguiendo claves específicas. Más del 90% de los huevos de las tres especies defoliadoras son depositados en los folíolos y ubicados mayormente en el nivel superior y medio de las plantas. A lo largo del desarrollo del cultivo, las mayores densidades de huevos se registraron en etapas tempranas (estado vegetativo y floración) siendo menos abundantes durante la fructificación. El estudio de la distribución de los huevos de estas especies plaga en la planta aporta información necesaria para establecer estrategias preventivas para su control.

Oophagous biological control agents of T. absoluta naturally present in crops in South America (Buenos Aires and Tucumán Provinces, Argentina) and Europe (Lazio, Italia) were surveyed. A taxonomic list of species and the natural mortality rates caused by parasitism and predation are reported. Furthermore, the first record of Encarsia porteri (Mercet) (Hymenoptera: Aphelinidae) parasitizing T. absoluta eggs is informed.

En este estudio se evaluaron los agentes oófagos de T. absoluta de presencia espontánea en cultivos de tomate en Sudamérica (NOA y Cinturón Hortícola Platense, Argentina) y en Europa (Lazio, Italia). Se reporta el listado de especies encontradas y las tasas de mortalidad natural por parasitismo y depredación en cultivos de ambos continentes. Además, se informa el primer registro de Encarsia porteri (Mercet) (Hymenoptera: Aphelinidae) parasitando huevos de la polilla.

The fall armyworm (FAW) is the most important threat to corn crops in Argentina, and there exists very little up-to-date information on its actual pest status because the available literature was published more than 20 years ago. Therefore, field surveys were carried out in the northeast of Argentina, in order to establish the attack rates and injury levels of the pest in relation to the crop phenology. The study was carried out at two localities: Colonia Benítez, an agricultural region, and Tapenagá, a cattle-raising area. At each site two 1-ha plots were sown either with a Bt-corn expressing Cry 1F protein or with an untransformed corn germplasm. Optimal and late sowing was assayed and FAW larval abundance, relative age composition, attack rates and level of damage to corn were recorded. At the moment of the field experiments, Bt-corn was not affected by FAW larvae. However, untransformed germplasms were severely affected by FAW larvae, with an average of attacked plants of 18% or more. In contrast to data obtained 30 years ago, higher values of FAW density were registered. Levels of damage to corn plants were higher after the V4 stage. It was found that the sowing date affected the infestation levels and early seeding avoided high armyworm densities that develop later in the season; in northern Argentina, this was only relevant in agricultural areas.

El cogollero es la plaga más importante del maíz en Argentina, siendo escasa y desactualizada la información sobre su estatus como plaga en los últimos 20 años. Se llevaron a cabo estudios de campo a fin de establecer las tasas de ataque y los niveles de daño de la plaga en relación con la fenología del cultivo en el noreste de Argentina. El estudio se realizó en dos localidades: Colonia Benítez, zona agrícola, y Tapenagá, zona ganadera. En cada localidad se sembraron dos parcelas de una hectárea, una con maíz transgénico expresando la proteína Bt Cry 1F y la otra con su correspondiente isogénico no transformado. Se registraron para dos fechas de siembra: cantidad de larvas, composición relativa de edades, tasa de ataque y nivel de daño al cultivo. En el momento del ensayo de campo, el maíz Bt no fue afectado por la plaga; sin embargo, el isogénico (sin gen Bt) fue atacado con una media superior al 18% de plantas dañadas. Comparando con datos obtenidos hace 30 años en esta región, se obtuvieron mayores valores de densidad de larvas/planta. Los niveles de daño fueron mayores después de V4. La fecha de siembra incide en los niveles de infestación: siembras tempranas evitan las altas densidades del cogollero que se desarrollan durante el verano, pero para la región estudiada esto solo fue relevante en la zona agrícola.

Los Cicadellidae son una de las familias mejor representadas en la región neotropical. La tribu Proconiini incluye a muchos de los insectos que se alimentan de xilema y la mayoría de los vectores de organismos fitopatógenos asociados con dicho tejido de conducción. La citogenética de los Proconiini es prácticamente inexplorada. Por lo tanto, se utilizaron técnicas citogenéticas convencionales para describir el cariotipo y la meiosis en los machos de Tapajosa rubromarginata Signoret. Este cicadélido presenta el complemento cromosómico diploide de 2n=20A+X0 en los machos. Los cromosomas no presentan constricción primaria, son holocinéticos, y la meiosis es pre-reduccional, muestra un comportamiento similar tanto en los cromosomas sexuales como en los autosómicos durante la anafase I. En ese estado, los cromosomas se orientan de manera paralela a las fibras del huso acromático con actividad cinética en los telómeros y segregan de manera reduccional en la fase I y ecuacional en la fase II de la meiosis.

Cicadellidae in one of the best represented families in the Neotropical Region, and the tribe Proconiini comprises most of the xylem-feeding insects, including the majority of the known vectors of xylem-born phytopathogenic organisms. The cytogenetics of the Proconiini remains largely unexplored. We studied males of Tapajosa rubromarginata (Signoret) collected at El Manantial (Tucumán, Argentina) on native spontaneous vegetation where Sorghum halepense predominates. Conventional cytogenetic techniques were used in order to describe the karyotype and male meiosis of this sharpshooter. T. rubromarginata has a male karyological formula of 2n=21 and a sex chromosome system XO:XX (♂:♀). The chromosomes do not have a primary constriction, being holokinetic and the meiosis is pre-reductional, showing similar behavior both for autosomes and sex chromosomes during anaphase I. For this stage, chromosomes are parallel to the acromatic spindle with kinetic activities in the telomeres. They segregate reductionally in the anaphase I, and towards the equator during the second division of the meiosis. This is the first contribution to cytogenetic aspects on proconines sharpshooters, particularly on this economic relevant Auchenorrhyncha species. Rev. Biol. Trop. 59 (1): 309-314. Epub 2011 March 01.

Diatraea saccharalis (Fabr.) is considered the key pest of sugarcane crops in the Argentine northwest. The earwig Doru luteipes (Scudder) develops high populations on sugarcane, and in other regions it was depicted as a significant predator of diverse pest in corn, cotton, and cabbage crops. The aim of this contribution is to inform about different biological parameters of this Dermaptera, and to assess the predatory capacity of its nymphs by means of the estimation of consumption rates using Diatraea saccharalis eggs. Both field and laboratory observations were carried out. In the latter, 50 neonate nymphs were confined in glass tubes and 100 sugarcane borer eggs were provided daily. Information on different behavioral aspects is provided. In field conditions, the sex proportion is approximately 1:1; an average of 31 eggs were laid, and the emergence rate reached 95%. Egg incubation is complete within a range of 6-10 days, and pre-imaginal development has a mean duration of 37.6 days. Throughout the four nymphal instars, a single individual could consume an average of 591.3 sugarcane borer eggs. The potential implication of the given information in applied sugarcane borer control methodologies is discussed.

Diatraea saccharalis (Fabr.) es considerada la principal plaga de la caña de azúcar en el noroeste argentino. El dermáptero Doru luteipes (Scudder) desarrolla importantes poblaciones en dicho cultivo y ha sido descrito como predador de plagas en maíz, algodón y coles. El objetivo de este trabajo fue brindar información sobre algunos aspectos biológicos y estimar la capacidad de predación de las ninfas de Doru luteipes, a través de la tasa de consumo de huevos de Diatraea saccharalis. Se realizaron observaciones de campo y ensayos de laboratorio, en estos últimos se colocaron individualmente en tubos de ensayo, 50 ninfas de D. luteipes recién eclosionadas y se les ofrecía diariamente cien huevos de la plaga. La proporción de sexos de D. luteipes en campo fue de aproximadamente 1:1 y sus posturas presentaron una media de 31 huevos, con una tasa de emergencia cercana al 95%. El período de incubación se prolongó entre 6 y 10 días y el desarrollo de los estadios ninfales promedió los 37,6 días. Las ninfas pasaron por cuatro estadios y consumieron una media de 591,3 huevos de D. saccharalis. Estos resultados sugieren que D. luteipes desempeña un papel importante en el control natural de las poblaciones de D. saccharalis, por lo tanto, su presencia debería tenerse en cuenta al diseñar estrategias para controlar esta plaga.

Eudorylas schreiteri (Shannon) é registrada pela primeira vez como endoparasitóide da cigarrinha do milho Dalbulus maidis (DeLong & Wolcott) no norte da Argentina. Uma tabela das espécies neotropicais de pipunculídeos com hospedeiros conhecidos é apresentada.

The big-headed fly Eudorylas schreiteri (Shannon) is recorded for the first time as an endoparasitoid of the corn leafhopper Dalbulus maidis (DeLong & Wolcott) in Northern Argentina. A table of known Neotropical pipunculid-host associations is presented.

Se estudiaron los parasitoides de la chicharrita del maíz, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) en la provincia de Tucumán, Argentina. Las chicharritas atacadas por Dryinidae (Hymenoptera: Chrysidoidea) fueron colectadas en campos de maíz entre dic 2003 y abr 2005. Se obtuvieron driínidos de tres especies diferentes: Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi, y G. moyaraygozai Olmi. Se cita por primera vez a G. moyaraygozai en Argentina, y se describe al macho de dicha especie. Se registra por primera vez en campo la asociación parasitoide-hospedador de G. caraibicus y D. maidis; además, se mencionan por primera vez a G. contortus y G. moyaraygozai como parasitoides de la chicharrita del maíz. Se calculó la tasa de parasitoidización de G. moyaraygozai en campo.

The parasitoids of the Corn Leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) were studied in Tucumán Province, Argentina. Leafhoppers parasitized by Dryinidae (Hymenoptera: Chrysidoidea) were collected in cornfields from Dec 2003 to Apr 2005. Dryinid adults belonging to three species, Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi, and G. moyaraygozai Olmi, were obtained. G. moyaraygozai is quoted for the first time in Argentina, and the male is described for the first time. This contribution presents the first field host-association record for G. caraibicus and D. maidis; in addition, G. contortus, and G. moyaraygozai are cited for the first time attacking Corn Leafhopper populations. Data on the parasitization rate by G. moyaraygozai are given.

Os parasitoides da cigarrinha do milho, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Auchenorrhyncha) foram estudados na província de Tucumán, Argentina. As cigarrinhas atacadas por Dryinidae (Hymenoptera: Chrysidoidea) foram colectadas em cultivos de milho entre dezembro de 2003 e abril de 2005. Foram obtidos dryínidos de três espécies diferentes: Gonatopus caraibicus (Olmi), Gonatopus contortus Olmi e Gonatopus moyaraygozai Olmi. G. caraibicus, anteriormente obtido de D. maidis sómente em laboratório, foi criado também em campo. Pela primeira vez G. contortus e G. moyaraygozai são citados como parasitoides de D. maidis. De G. moyaraygozai, citado pela primeira vez em Argentina, foram obtidos ambos os sexos; a descrição do macho, anteriormente desconhecido, é feita pela primeira vez. A taxa de parasitismo de G. moyaraygozai foi avaliada em campo.

A comparative laboratory study on population parameters of Spodoptera frugiperda (Smith) (Lep.: Noctuidae) fed on corn (Zea mays L.) and two of the most predominant grasses in Tucuman (Argentina) Guineagrass (Panicum maximum Jacq.) and Bermudagrass (Cynodon dactylon (L.) Pers.) was carried out. The diets used determined changes in diverse parameters such as duration of life cycle, number of larval instars, sex ratio, life expectancy, fertility and/or fecundity. Regarding to the life cycle duration, significant differences among host plants were recorded for the different developmental stages. Females fed on a corn diet showed a fertility of 92.1%, while those breeding on a diet based on Guineagrass showed 96.4% and 99.8% on Bermudagrass. Mean daily egg production ranged within 99.4 (fed on Bermudagrass) and 187.8 (fed on Guineagrass). Total mean egg production also varied with larval diet; maximum value was recorded for females fed on Guineagrass leaves (0 1282.7 ± 38.6 eggs/females). Results suggest that individuals bred on this grasses during final winter could play an important role in FAW population dynamic performance affecting corn crops in Argentina's Norther Region.

Se realizó un estudio comparativo en condiciones de laboratorio sobre los parámetros poblacionales de S. frugiperda alimentada con maíz (Zea mays L.) y con las dos pasturas más predominantes en Tucumán (Argentina): pasto guinea (Panicum maximum Jacq.) y gramón (Cynodon dactylon (L.) Pers.). Las dietas usadas determinaron cambios en diversos parámetros tales como duración del ciclo de vida, número de instares larvales, proporción de sexos, expectativa de vida, fertilidad y fecundidad. Teniendo en cuenta la duración de ciclo de vida, diferencias significativas entre las plantas huésped fueron registradas entre los distintos estados de desarrollo. Las hembras mostraron una fertilidad del 92,1%, 96,4% y 99,8% cuando fueron alimentadas con maíz, pasto guinea y gramón, respectivamente. La producción diaria media de huevos varió entre 99,4 para hembras alimentadas con gramón y 187,8 para las alimentadas con pasto guinea. La producción media total de huevos también varió según la dieta suministrada, el máximo valor fue registrado para las hembras que durante el estadío larval fueron alimentadas con hojas de pasto guinea (0 1282.7 ± 38.6 huevos/hembras). Los resultados sugieren que los individuos alimentados con las pasturas antes mencionadas jugarían un papel importante en el comportamiento de la dinámica poblacional de S. frugiperda afectando cultivos de maíz en la región del Norese Argentino. Estas pasturas podrían albergar a la primera generación anual de la plaga y su manejo racional podría disminuir la incidencia del cogollero sobre los cultivos de maíz.

The objective of this contribution is to mention Gonatopus chilensis Olmi (Dryinidae: Gonatopodinae) as a new host for the encyrtid Cheiloneurus cupreicollis Ashmead, and enlarge the geographic distribution of the parasitoid to Catamarca province (Santa María).

El objeto de la presente contribución es informar sobre el comportamiento parasitoide del encírtido Cheiloneurus cupreicollis Ashmead sobre Gonatopus chilensis Olmi (Dryinidae: Gonatopodinae), y ampliar su distribución geográfica a la provincia de Catamarca (Santa María).

A incidência de doenças causadas por molicutes e por vírus foi avaliada em lavouras de milho (Zea mays) nas Províncias de Tucumán e de Córdoba, na Argentina, em fevereiro de 2000. Na Província de Tucumán verificou-se que 44% das lavouras apresentaram altos níveis de incidência de plantas com sintomas de enfezamentos causados por molicutes (50 a 100%), em altitudes variando de 300 a 2.000 m. A presença de fitoplasma e de espiroplasma foi confirmada em amostras de folhas de plantas com sintomas de enfezamentos, através dos testes de PCR e de "Western blotting". Constatou-se, porém, que a eficiência desses testes para detecção destes patógenos, quando os sintomas apresentados pelas plantas eram muito acentuados, foi da ordem de 70%, e de apenas 30% quando os sintomas eram menos acentuados. Na localidade Jesus Maria, foram encontradas plantas apresentando acentuado nanismo, folhas estreitas e com deformações. Dentre quatro amostras destas plantas, submetidas a testes de PCR, em duas foi detectada a presença de fitoplasma, possivelmente d istinto do "Maize Bushy Stunt Phytoplasma". A cigarrinha Dalbulus maidis, inseto vetor dos molicutes, foi encontrada apenas em Tucumán, estando ausente em Córdoba. O Mal de Rio Cuarto virus foi detectado em seis lavouras em Córdoba, e em três em Tucumán. A cigarrinha Delphacodes kuscheli foi detectada em todas as lavouras em Córdoba, e em apenas três lavouras em Tucumán. O Maize dwarf mosaic virus foi detectado em cerca de 60% das lavouras amostradas nas duas Províncias e o Maize rayado fino virus em apenas uma localidade em Tucumán.

The incidence of "corn stunt diseases" and maize (Zea mays) viruses was evaluated in maize fields located at the Provinces of Tucumán and Córdoba in Argentina in February 2000. A high number of plants infected with "corn stunt disease" were observed in Tucumán (up 50 to 100%) in 44% of maize crops surveyed in areas varying from up 300 to 2000 m high. The presence of Maize Bushy Stunt Phytoplasma (MBSP) and Corn Stunt Spiroplasma (CSS) was confirmed by PCR and Western blotting tests. In plants showing typical symptoms of MBSP or CSS, the pathogens were detected in 70% of the samples. However, when symptoms were weak, the efficiency of detection dropped to approximately 30%. In Rio Cuarto, Province of Córdoba, the presence of phytoplasma was detected only in three plants showing red leaf symptoms. In Jesus Maria locality, plants showing symptoms different from those caused by MBSP, were demonstrated to be infected by phytoplasma when analyzed by PCR using universal primers. The leafhopper Dalbulus maidis, vector of MBSP and CSS, was found only in Tucumán. The Mal de Rio Cuarto virus (MRCV) was found in six maize fields in Córdoba and in three maize fields located at 1970 to 2.000 m high in Tucumán. The plant hopper Delphacodes kuscheli, vector of MRCV, was found in both provinces sampled. The Maize dwarf mosaic virus (MDMV) was found in 60% of maize crops in both Provinces and the Maize rayado fino virus (MRFV)was found only in one location in Tucumán.