Ana María Marino de Remes Lenicov

Feeding behavior of the vector Delphacodes kuscheli (Hemiptera: Fulgoromorpha: Delphacidae) on maize and oat

Abstract The planthopper Delphacodes kuscheli Fennah 1955 is an important pest affecting maize in Argentina. It transmits, in a persistent way, Mal de Río Cuarto virus (MRCV) (Reoviridae, Fijivirus) which has been reported to cause a severe loss in maize crops (Zea mays L.). The present study reports on the feeding behavior of the vector (adults and immature instars) on oat (preferential host) and maize (non-preferred host). Feeding sites and salivary sheaths were detected through histological sections of leaves. The location of salivary sheath terminations and the honeydew excretion analysis revealed that D. kuscheli feeds on phloem sap in both hosts. On maize, the high number of sheaths ending in the mesophyll and their particular disposition (parallel to the leaf surface and across the vascular bundles) strongly suggest the non-preference of the vector to feed on this species. On both hosts, immature instars showed similar feeding behavior to adults indicating the capacity to transmit the virus along the life period.

A New Species of Taosa (Hemiptera: Dictyopharidae) from South America Associated with Water Hyacinth

ABSTRACT A new species of Taosa (Hemiptera: Dictyopharidae) is described, All the stages were collected on the aquatic weed Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) at several localities on the Paraguay River in Argentina, and in the upper Amazon River in Perú. Taosa (Cuernavaca) longula Remes Lenicov sp. nov. is distinguished by the following coloration pattern and morphological features: uniform green coloration with apair of lateral small dark spots on mesonotum, vertex subquadrate with a closed triangular facet well defined on apex, and a long anal segment; in male, the shape and relative length of parameres, the tubular aedeagus with a pair of ventral spinose processes recurved upward; in the female, the length, shape and denticulation of the first valvulae of the ovipositor, To facilitate the comparison of the new species with the morphologically allied, Taosa inexacta (Walker) and Taosa herbida (Walker 1851), a key is included. Further information on reproductive and feeding behavior, host plants, and geographical distribution of this species are given.

Tagosodes orizicolus: nuevo vector potencial del Mal de Río Cuarto virus

An important disease affecting the yield of corn crops is known as mal de Rio Cuarto. Delphacodes kuscheli is the most important vector. The objective of this work was to determine the vector capacity of a new species, Tagosodes orizicolus, both in the field and under experimental conditions. Transmission trials were carried out on both species simultaneously. For acquisition, latency and infection the times considered optimum for D. kuscheli were used. The plants were analyzed by DAS-ELISA. Salivary glands of T. orizicolus were observed by electron microscopy. In experimental tests, values of percentages of transmission of 10% for T. orizicolus and 42% for D. kuscheli were obtained. The ultra-fine sections of the salivary glands of T. orizicolus showed the aggregation of viral particles 70 nm in diameter. Vectoral capacity could not be proven under natural conditions from a test conducted with insects captured in the field. Likewise, for the first time wheat, barley and triticale are mentioned as suitable crops for breeding T. orizicolus. These results show T. orizicolus to be a species of epidemiological interest in the northeast of Argentina due to the proven capacity of acquiring and transmitting this viral agent under experimental conditions.

Diversity of Auchenorrhyncha (Hemiptera: Cicadellidae: Delphacidae) Associated with Vicia villosa in Southern Buenos Aires Province, Argentina

Abstract Among the Hemiptera, the Auchenorrhyncha are well known owing to their phytosanitary relevance since the group includes pathogen vector species able to damage commercial crops. Vicia villosa Roth (Fabaceae) is a fodder plant species, mainly distributed in central Argentina. Previous contributions have shown that V. villosa is colonized by diverse species of Auchenorrhyncha, either naturalized or native to valley of Colorado River area, in southern Buenos Aires province. To date, the only information about the species of hoppers associated with Vicia has come from preliminary field observations. The dearth of demographic knowledge about these phytophagous insects associated with this crop in Argentina motivates the study. The aims of this work were: 1) to characterize the diversity of the species of Auchenorrhyncha associated with V. villosa and 2) to determine the seasonal fluctuation of the most abundant species in relation to local weather variables and crop phonological phases. The study was conducted in Vicia plots located at EEA INTA Hilario Ascasubi (S 39° 23′ 36″ -W 62° 37′ 59″, 15 m.a.s.l.) southern Buenos Aires province. The specimens were collected with a sweep net during 2 yr (2009 and 2011). Weather variables were recorded using a meteorological station located at the sampling site. To measure species richness and community diversity we calculated both Margalef (DMg) and the Simpson (D) indexes, and also, the Relative Importance Index (RII). The relationships between population densities of the leafhoppers, Paratanus exitiosus (Beamer) and Agalliana ensigera Oman (Cicadellidae), with weather variables were analyzed through simple and multiple linear regression. A total of 17 species were associated with V. villosa crops in Argentina, of which 15 belong to the Cicadellidae and 2 to the Delphacidae. Abundance and species richness were higher in 2009 than in 2011. In general, the results of the Margalef index showed that species richness was higher in 2009, while Simpson Index (D) indicated a higher dominance in 2011 than in 2009. The species, P. exitiosus and A. ensigera, stood out for their abundance, frequency and phytosanitary relevance during the sampling period. Both species presented population increases since Nov coinciding with different phenological phases of the crop and the maximum density of the canopy. Additionally, the population density of P. exitiosus showed strong dependence on the hydric balance and photoperiod, while A. ensigera was influenced by Degree-days10 and hydric balance. Vicia villlosa was a new host-plant record for 15 species. Buenos Aires province was cited as a new distribution record for 2 species.

A new genus and species of Delphacini (Hemiptera: Fulgoromorpha: Delphacidae) associated with hydrophytic plants in Argentina.

Abstract A new delphacid genus and species from Argentina, Lepidelphax pistiae Remes Lenicov, gen. et sp. nov.(Hemiptera: Fulgoromorpha: Delphacidae: Delphacini), is described and illustrated, and biological, distribution and experimental host range data are provided. Males of the new genus are easily distinguished from all other Neotropical Delphacini by being pale cream to white in color with a distinctive pair of longitudinal stripes on the face and symmetrical dark brown to black spots on the thorax and abdomen; very slender, laterally compressed, with long legs, narrow and short vertex with a small sub-apical areola continued by a distinctively simple frontal median carina. It also has unique malegenital structures. Laboratory and field data indicate this species is a specialized herbivore that feeds and oviposits exclusively on Pistia stratiotes (Alismatales: Araceae), a floating macrophyte native to South America. Lepidelphax pistiae was found throughout the distribution of P. stratiotes in Argentina.

ABUNDANCE AND SPECIES RICHNESS OF LEAFHOPPERS AND PLANTHOPPERS (HEMIPTERA: CICADELLIDAE AND DELPHACIDAE) IN BRAZILIAN MAIZE CROPS

Abstract Insects in the Cicadellidae and Delphacidae families, common in grasses, are an important group of vectors of viruses and mollicutes, which cause diseases in several plant species. The goal of this study was to evaluate the abundance and species richness of Cicadellidae and Delphacidae and the presence of potential vectors of viruses and mollicutes in maize crops in Brazil. Insects were collected using sweep nets in maize crops in 48 counties of 8 states, distributed in 4 regions of Brazil in the yr 2005, 2006 and 2007, with a total of 198 samples. The collected material was screened, and the leafhoppers and planthoppers were identified at the species level. A total of 4233 Cicadellidae specimens, including 30 species, and 205 Delphacidae specimens, including 9 species, were collected. The most abundant species was Dalbulus maidis (Delong & Wolcott) representing 90.1% of leafhoppers and planthoppers. Abundance and species richness differences were observed between the northeast and center-south regions of Brazil. Eight species of leafhoppers and planthoppers were identified as vectors or potential vectors of viruses and mollicutes in maize, although some of these viruses are not reported in Brazil. Among these species, we identified the planthoppers, Caenodelphax teapae (Fowler), Peregrinus maidis Ashmed, Pyrophagus tigrinus Remes Lenicov & Varela and Toya propinqua (Fieber) are experimental vectors of Mal de Río Cuarto virus, which is a quarantine virus in Brazil. Two Cicadellidae species and 3 Delphacidae species were reported for the first time in Brazil.

FIRST BIOLOGICAL DATA OF CERESA NIGRIPECTUS (HEMIPTERA: MEMBRACIDAE), A COMMON TREEHOPPER ON ALFALFA CROPS IN ARGENTINA

Abstract Alfalfa (Medicago sativa L.; Fabaceae) is essential for argentinean agricultural development, but diseases like “witches´; broom«, caused by the ArAWB phytoplasma, are limiting factors for the production of this crop. Insects that visit alfalfa have been poorly studied. The treehopper, Ceresa nigripectus Remes Lenicov (Hemiptera: Membracidae) is very frequent in alfalfa crops; ArAWB was detected in several individuals of this treehopper, but the ability of this species to transmit the pathogen has not yet been demonstrated. The Membracidae family is a poorly studied group in Argentina. No data on the biology of C. nigripectus are available, and therefore the aim of this contribution is to provide information on its behavioral and biological parameters as a first step toward its control. The studies were conducted in the laboratory under controlled conditions. Ceresa nigripectus populations were maintained on healthy alfalfa plants; the treehoppers were checked daily, the occurrence of molts was noted, and diverse aspects of nymphal and adult behavior were also recorded. A life table was built combining the observational data from 7 cohorts. Oviposition sites were characterized by dissecting plants and through staining methods. Ceresa nigripectus could complete its life cycle entirely by using only alfalfa as a host. Females do not tend their broods. Eggs are laid individually and rarely 2 or 3 were found in the same slit. Eggs were located in the stems, in the nodes (in the axils of the leaves) or in the internodal space, between the epidermis and cortical tissues. The pre-ovipositional period was about 6 days, and the average duration of the egg stage was 20 days. The duration of nymphal period was variable, between 32 to 63 days, with a mean of 45 days. Two periods of high mortality were recognized, i.e., in the first instar, and during the second week of the adult stage. Longevity of adults averaged 61 days, but some individuals survived up to 202 days; females lived longer than males. In laboratory colonies, the sex ratio was about 1.3:1 females:males. All the developmental stages of the treehopper were tended by the ant Camponotus punctulatus Mayr. Data regarding behavioral aspects and new distributional information are also provided.

Description of the immature stages of Delphacodes kuscheli Fennah (Hemiptera: Delphacidae), vector of “Mal de Río Cuarto virus” on maize in Argentina

Delphacodes kuscheli Fennah is the most efficient vector of Mal de Río Cuarto virus (MRCV) maize disease in Argentina, which is caused by a persistently transmitted fijivirus. Delphacodes kuscheli is abundant in a wide area of Central Argentina (32–35°S), affecting oat, wheat and maize crops, and weeds. All five immature instars of D. kuscheli are described, keyed and illustrated. A key is provided to highlight the main features for identification of the fifth‐instar nymphs of three other Delphacid species on maize. Adults of D. kuscheli were reared under controlled conditions in individual glass cages containing oat plants. The description of each instar was based on 1‐day‐old nymphs. Coloration pattern, shape of frons, length of the rostrum segments, and length, shape and number of spur teeth are useful features for identification of the fifth nymphal instars of these species.

Modeling population dynamics of yeast-like symbionts (Ascomycota: Pyrenomycetes: Clavicipitaceae) of the planthopper Delphacodes kuscheli (Hemiptera: Delphacidae)

Delphacodes kuscheli establish mutualistic relationship with yeast-like symbionts (YLS) that live in the fat body and are necessary for host survival and reproduction. We estimated for a host of age t, its body weight, W(t), and the number of YLS per host, YLS(t). The host body weight was calculated as: W(t) = Lm/[1+ e (d–kt)], (Lm = the maximum observed weight, and d and k are constants), and the fat body was considered a fixed proportion of W(t). We calculated the number of YLS per unit host body mass: α(t) = YLS(t)/W(t). We also calculated the number of YLS per host, cYLS(t), and analyzed the pattern of variation in both sexes adapting the expression of the logistic model: cYLS(t) = KNoert/K+(ert -1)No, (No = initial number of YLS, r = intrinsic per capita rate of natural increase, and K = variable carrying capacity). In females the carrying capacity varied according to a constant proportion of the host’s weight: K(t) = αW(t). In males α(t) was considered a decreasing function of the host age: K(t) = α(t)W(t). The coefficients No, α, and r were subjected to parameterization. We found that the patterns of W(t) and YLS(t) of D. kuscheli were similar to other planthoppers. In females YLS increased up to the adult stage and then remained almost constant, varying similarly to individual weight. In males YLS increased up to the 5th instar nymph as the individual weight did, but the number of YLS decreased in the adult stage and the correlation was not so good. The calculated number of YLS per host matches reasonably well with the number estimated experimentally both in females and males. This is the first study that quantified and modeled the dynamics of YLS endosymbionts in a Neotropical planthopper pest. The models will be used in future studies for better understand the experimental reduction of YLS in young nymphal stages.

Description of the immature stages and new host plant records of Deois ( Deois ) mourei (Berg) (Hemiptera: Cercopidae), a species newly recorded from Argentina and Paraguay

Deois (Deois) mourei Cavichioli & Sakakibara (Hemiptera: Cercopidae) is recorded for the first time from Argentina and Paraguay. The eggs and immature stages of the species are described and illustrated; the main characters that distinguish instars are body size, color, number of flagellomeres, and number of tibial and metatarsomere spines. A key for identification of nymphs of D. (D.) mourei and a key to differentiate nymphs of the sympatric species D. (D.) mourei and Notozulia entreriana Berg are provided. In addition, a list of host plants of D. (D.) mourei in Argentina is given.