Contributions to the knowledge of the Cicadellini sharpshooters (Hemiptera: Cicadellidae) associated with citrus orchards in Argentina.

Xylella fastidiosa Wells et al. is a xylem-borne bacterium that causes some of the most important plant diseases to woody plants such as citrus, olives, almonds and other cultures. This pathogen is mainly transmitted by sharpshooters, among which the tribe Cicadellini (Cicadellinae) includes the largest number of proven vectors. The correct identification of the vectors, along with biological and phenological information, are necessary to identify the key vectors involved in the spread of the bacterium and, consequently, establish control strategies and evaluate risks at a local or regional scale. However, lack of information on the Cicadellini from Argentina has delayed the implementation of control measures. Based on surveys conducted in the main citrus producing areas along with bibliographic data, this contribution provides the first list of Cicadellini species from Argentina that are potential vectors of X. fastidiosa; an identification key to these sharpshooters is provided. Twelve species were recorded from northeastern citrus groves, while from northwestern orchards, with previous information totally absent, 10 species were recorded. Eight species are shared by all producing regions, and five of them are proven vectors of X. fastidiosa (Bucephalogonia xanthophis (Berg), Dilobopterus costalimai Young, Macugonalia cavifrons (Stål), M. leucomelas (Walker), Sonesimia grossa (Signoret)). This contribution provides 22 new insect-plant relationships, information on their natural enemies, the geographic distribution of all species is broadened and the female genitalia of three proven vectors are described for the first time.

Ovigeny strategy of the parasitic wasp Cosmocomoidea annulicornis (Hymenoptera: Mymaridae): effect of female age, feeding and host availability on reproductive traits.

The reproductive traits of the mymarid wasp Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) attacking eggs of the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae) were evaluated under laboratory conditions. Bioassays were carried out to estimate the realized fecundity and egg load of females. The ovigeny index was calculated and different biological traits, such as body size, oöcyte length, gaster length and wing length, were analysed to assess significant associations between these traits and the species fitness. In addition, the effect of host availability and feeding on longevity and potential fecundity throughout life and the effect of female age on egg maturation dynamics were assessed. The results showed that C. annulicornis is a strongly synovigenic species. A positive correlation was found between fecundity and longevity of the females and between body size and oöcyte length. Contrary to expected, body size was not related to fecundity and longevity. Females lived significantly longer in the presence of hosts and honey than when they were host-deprived and honey-fed or both host and honey deprived. Host availability had a significant effect on the amount of eggs laid by C. annulicornis females. Female age was negatively associated with oöcyte length. Furthermore, females were able to mature additional eggs as they aged, nevertheless, when host-deprived, senescent females presented significantly less mature eggs than younger ones, suggesting a possible egg oosorption. These results might contribute to a better understanding of the reproductive potential of this species as a biocontrol agent.

Influence of the site of oviposition on the level of egg parasitism in the corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae).

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.

Modern Maize Hybrids Have Lost Volatile Bottom-Up and Top-Down Control of Dalbulus maidis, a Specialist Herbivore.

Following damage by herbivores, many plants release volatiles that dissuade future conspecifics from feeding. In many crop plants however, induced volatiles mediating this kind of interactions among plants, herbivores and also their natural enemies have been altered through the process of domestication. The selection of crops for increased yield may have gone at a cost of defense, possibly including defense-related volatiles. Dalbulus maidis (Hemiptera: Cicadellidae), a specialist leafhopper that only feeds on Zea spp., is a vector of Corn Stunt Spiroplasma, a serious maize disease. Here, we compared the volatiles released following D. maidis attack by a maize landrace and two maize hybrids of temperate and tropical background. Also, we performed behavioral assays with the leafhopper contrasting healthy non-attacked maize seedlings versus attacked seedlings. The maize landrace produced more than 6-fold larger quantities of induced volatiles compared to the maize hybrids after herbivory. Corn leafhopper females were able to detect and significantly preferred the odors of healthy seedlings over the attacked ones only in the landrace. They did not discriminate between the attacked and non-attacked hybrids. Additionally, we found that the attraction of the parasitoid wasp Anagrus virlai (Hymenoptera: Mymaridae) to its host was diminished in the tested hybrids. The parasitoid was able to detect the odors of the attacked landrace, however it was unable to discriminate between healthy and attacked maize hybrid plants. These results suggest that those more domesticated germplasms may have lost the ability not only to release volatiles that avoid colonization of future herbivores, but also to attract their natural enemies in a tritrophic system.

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.

Preliminary Observations on Zelus obscuridorsis (Stål) (Hemiptera: Reduviidae) as Predator of the Corn Leafhopper (Hemiptera: Cicadellidae) in Argentina.

The corn leafhopper Dalbulus maidis (Hemiptera: Cicadellidae), is an important corn pest in most of tropical and subtropical America. This leafhopper has a rich natural enemy complex of which parasitoids and pathogens are the most studied; knowledge on its predators is limited. We noted the presence of the native assassin bug Zelus obscuridorsis (Hemiptera: Reduviidae) predating diverse motile insects, including the corn leafhopper, on corn plants cultivated in household vegetable gardens in San Miguel de Tucumán (Argentina); in order to verify its predatory actions, we exposed lab-bred individuals of D. maidis to adults of Z. obscuridorsis. The predators were starved for 24 h before trials in which the corn leafhopper in different developmental stages were exposed. Zelus obscuridorsis is highly skilled in catching specimens in motion, but it was not able to prey on eggs. The predator was capable to catch and prey on nymphs and adults.

Egg parasitoids of the corn leafhopper, Dalbulus maidis, in the southernmost area of its distribution range.

Egg parasitoids of the corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae), were surveyed exposing sentinel eggs of the leafhopper along a latitudinal transect of 600 km in Argentina, the southernmost area of its distribution range. Four parasitoid species were obtained: the mymarids Anagrus breviphragma Soyka (Hymenoptera: Mymaridae), Anagrus flaveolus Waterhouse, and Polynema sp., and the trichogrammatid Pseudoligosita longifrangiata (Viggiani) (Hymenoptera: Trichogrammatidae). The low parasitism rate, low species richness, and high proportion of generalist egg parasitoids were quite clear in the southern distribution limit of the vector, in contrast to regions where corn crops are available all year round and there are continuous and overlapping generations of the pest. Further studies need to be done in order to determine the native host of the above egg parasitoids, the seasonal abundance, and the possible occurrence of other species affecting D. maidis populations in the studied area.

Proconiini sharpshooters of Argentina, with notes on its distribution, host plants, and natural enemies.

The American tribe Proconiini (Hemiptera: Cicadellidae: Cicadellinae) is one of the largest groups of xylem-feeding insects and includes the majority of the known vectors of xylem-born phytopathogenic organisms. The significance of the pathogens that this group transmits gives them an important role as pests, mostly for citrus fruit, grapes, and almonds. Knowledge of these Hemiptera in Argentina is insufficient and fragmentary. Thus one of the aims of this paper is to summarize the available information of the Proconiini sharpshooters in Argentina. In addition, 14 species are mentioned for the first time in the country, and new distributional data are given for 18 species. Thirty-four new associations between sharpshooters and host plants are recorded. New records of egg parasitoids are given for Dechacona missionum, Molomea consolida, M. lineiceps, and Tapajosa similis.

Characterization of the earwig, Doru lineare, as a predator of larvae of the fall armyworm, Spodoptera frugiperda: a functional response study.

Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) is considered as the most important pest of maize in almost all tropical America. In Argentina, the earwig Doru lineare Eschscholtz (Dermaptera: Forficulidae) has been observed preying on S. frugiperda egg masses in corn crops, but no data about its potential role as a biocontrol agent of this pest have been provided. The predation efficiency of D. lineare on newly emerged S. frugiperda larva was evaluated through a laboratory functional response study. D. lineare showed type II functional response to S. frugiperda larval density, and disc equation estimations of searching efficiency and handling time were (a) = 0.374 and (t) = 182.9 s, respectively. Earwig satiation occurred at 39.4 S. frugiperda larvae.

Occurrence of the Tamarix Leafhopper, Opsius stactogalus Fieber (Hemiptera: Cicadellidae), in Argentina.

The paleartic tamarix leafhopper, Opsius stactogalus Fieber (Hemiptera: Cicadellidae), can reduce the growth of tamarisk due to the aggregate feeding imposed by their populations. The species was mentioned for Argentina in Metcalf's catalogue (1967) without locality or region reference, and the contributions on Cicadellidae published by many authors after Metcalf omitted this distributional data. Populations of O. stactogalus on Tamarix sp. were found in 12 sites between 28 degrees 48' to 39 degrees 17' S and 64 degrees 06' to 70 degrees 04' W, located in both the Neotropical and Andean biogeographic regions.

Sustainable synthesis of flavonoid derivatives, QSAR study and insecticidal activity against the fall armyworm, Spodoptera frugiperda (Lep.: Noctuidae).

A simple, clean, solvent-free preparation of flavones by the use of a silica-supported Preyssler heteropolyacid as reusable catalyst is described. High selectivity and very good yields (87-94%) were obtained in short reaction times (7-13 min). Bioassays for insecticidal activity against Spodoptera frugiperda were carried out with a set of flavones. Bioassays showed that some of the flavones had moderate insecticidal activity. Quantitative structure-activity relationships were established on the available data with the purpose of predicting the insecticidal activity of a number of structurally related flavones. A relationship between the molecular structure and biological activity is proposed.

Characterization of native Bacillus thuringiensis strains and selection of an isolate active against Spodoptera frugiperda and Peridroma saucia.

Twelve Bacillus thuringiensis (Bt) strains, isolated from larvae and soil samples in Argentina, were molecularly and phenotypically characterized and their insecticidal activities against Spodoptera frugiperda and Peridroma saucia were determined. One isolate--Bt RT--produced more than 93% mortality on first instar larvae of both species, which was higher than that produced by the reference strain Bt 4D1. Bt RT carried a different cry gene profile than Bt 4D1. Scanning electron microscopy showed the presence of bipyramidal and cuboidal crystals. Phenotypic characterization revealed lytic enzymes that could contribute to Bt pathogenicity.

First record of Eudorylas schreiteri (Shannon) (Diptera: Pipunculidae) as a parasitoid of the corn leafhopper (Hemiptera: Cicadellidae) in Argentina, with a table of pipunculid-host associations in the neotropical region.

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.

First record of Eudorylas schreiteri (Shannon) (Diptera: Pipunculidae) as a parasitoid of the corn leafhopper (Hemiptera: Cicadellidae) in Argentina, with a table of pipunculid-host associations in the neotropical region / Primeiro registro de Eudorylas schreiteri (Shannon) (Diptera: Pipunculidae) como parasitóide da cigarrinha do milho (Hemiptera: Cicadellidae) na Argentina, e uma tabela dos hospedeiros de pipunculídeos na região neotropical

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.

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.

Insecticidal crystal proteins from native Bacillus thuringiensis: numerical analysis and biological activity against Spodoptera frugiperda.

Fourteen strains of Bacillus thuringiensis collected from both larvae showing disease symptoms and soil samples in northwest Argentina were characterized by insecticidal activity against Spodoptera frugiperda. First instar larvae and protein profile SDS-PAGE analysis of whole cell proteins not only allowed the differentiation of native Bacillus thuringiensis but also revealed the possibility of applying protein profile analysis in classification of toxicity patterns. Cluster analysis showed that there were two main groups. Interestingly, one of them only contained the most pathogenic native strains. The biomass-bound protease activity of native pathogenic isolates and the reference strain Bt 4D1 is also reported.

Dryinidae (Hymenoptera: Chrysidoidea) parasitoids of the corn leafhopper, Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae), in Argentina, with description of the male of Gonatopus moyaraygozai Olmi

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.