Search

The corn leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) is the vector of the Corn stunt disease, caused by a complex of pathogens, a serious threat to corn production in tropical and subtropical regions of the American continent. The aim of this study was to conduct an exploratory analysis to estimate the structure and genetic differentiation of D. maidis populations from three geographical regions collected during two maize growing seasons in northwestern Argentina using inter -simple sequence repeats (ISSR) markers. Populations in the High -elevation Valley and Dry Plain sites, despite being geographically separated by mountains of high elevations, were genetically similar, while the nearest populations located in Dry Plain and Humid Piedmont were the most genetically different. The results suggested that populations of D. maidis in subtropical maize-growing areas are structured according to the climatic conditions, mainly humidity and precipitation. Additionally, this structure might be influenced by annual migrants from northern tropical areas, as well as by individuals that occasionally survive from one season to the next as occurs in the Humid Piedmont. Darker body coloration of females sampled during the second year in Dry Plain and Humid Piedmont might be associated with colder temperatures during the winter before maize cultivation. This study is the first conducted in Argentina on the genetic div ersity of populations of D. maidis. The results presented here highlight the need for further investigation into the origin and potential movement of D. maidis populations. Knowing how the crop is colonized will aid in the development of well - fitting models, for preventing the disease caused by the pathogens transmitted by this insect. [ABSTRACT FROM AUTHOR]

Delphacodes kuscheli Fennah (Hemiptera: Delphacidae) is the main planthopper vector of Mal de Río Cuarto virus (MRCV), a Fijivirus that severely affects maize production in Argentina. The effect of several nutritional sources on the virulence of Beauveria bassiana s.l. CEP147 (Balsamo‐Crivelli) Vuillemin (Hypocreales: Cordycipitaceae) against this planthopper was evaluated with the aim to select some of them to be incorporated in future mass production studies. Ten agar‐agar 2% media were used. Media were supplemented with 10 g of sucrose and 4% flour of either amaranth, chia, flax, oat bran, parboiled rice, poppy, quinoa, or wheat germ. Sabouraud dextrose agar with 1% yeast extract (SDAY) was used as control, and sucrose agar medium supplemented with 2% chitin was used as a possible inductor of enzymatic activity. We evaluated the effect of each medium on colony growth, conidial yield, viability, size, adherence, hydrophobicity, protease activity, cumulative mortality, and median survival time (MST). Principal component analysis indicated that conidial viability and adherence explained the most of the total variance, indicating that these variables can be used as indicators of fungal virulence. Medium supplemented with chia flour not only increased conidial viability (100%) and adherence (0.09 A550) with respect to the control medium, but also produced high D. kuscheli mortality (91.7%), with the lowest MST (5.2 days). We suggest that chia flour, which is rich in carbohydrates, proteins, vitamins, and minerals, might be incorporated as a nutritional supplement to solid substrates in order to increase the virulence of B. bassiana s.l. CEP147 against this and other pests. However, future studies are necessary to evaluate the effectiveness of this nutritional source on solid‐state fermentation. [ABSTRACT FROM AUTHOR]

Delphacodes kuscheli is the most important natural vector of Mal de Río Cuarto virus (MRCV) in Argentina, a Fijivirus (Reoviridae) that causes important economic losses on maize production. Although this planthopper does not breed successfully on maize, virus transmission occurs when adults migrate from oat, a winter host and a reservoir of the virus, to maize. Probing behaviour on both hosts was recorded and analysed using the direct current electrical penetration graph (DC‐EPG) system. Eight main waveforms were identified during probing behaviour by D. kuscheli. These waveforms were interpreted with reference to that described for delphacids and were related to putative probing activities: np (non‐penetration or non‐probe); N1, N2 and N3 (stylet pathway: penetration, salivation, stylet movement and extracellular activities near the phloem region); N4‐a (sieve element salivation); N4‐b (phloem sap ingestion); N5 (xylem activity); and N6 (derailed stylet mechanics). The EPG variables showed that on maize, D. kuscheli exhibited longer periods of non‐probe and longer time from first probe to first phloem activity, with a higher percentage of probing spent in stylet pathway and xylem phase than on oat. Furthermore, on maize, fewer insects showed phloem phase activities (N4‐a and N4‐b) and sustained phloem ingestion than on oat, and the time on phloem ingestion was shorter than on oat. The constrained behaviour of D. kuscheli on maize suggests that plant resistance factors may be involved. [ABSTRACT FROM AUTHOR]

Delphacodes kuscheli, the main vector of maize Mal de Río Cuarto disease in Argentina, was used to analyze the effect of food quality on wing-form, demographic traits and number of yeast-like symbionts (YLS). First instar nymphs were caged on the leaf apex or on the ligular zone of oat plants, characterized by having low and high nutritional value respectively, and followed in their development to adulthood. Food quality affected the proportion of wing morphs, with an increased number of brachypterous individuals on the higher food quality zone. Macropterous and brachypterous females from the ligular zone had higher survivorship, shorter development time and higher number of YLS. For males, development time and number of YLS did not differ significantly in individuals fed from both zones, while body and wing length were superior in individuals fed on the ligular zone. Results suggest that females allocate the resources from feeding on a richer zone to reduce the pre-reproductive period and to increase the number of YLS, and males acquire a larger size while maintaining development time and YLS number. This is the first study quantifying the variation of number of YLS according to food quality in a Neotropical planthopper pest. [ABSTRACT FROM AUTHOR]

Delphacodes kuscheli, a phloem sap-sucking planthopper and the main vector of the Mal de Río Cuarto virus (MRCV) of maize in Argentina, was used to analyze phenotypic plasticity in behavior and demographic traits in response to different food quality, without masking the effects of density dependence and within-plant heterogeneity. We evaluated selectivity of nymphs and adults for different sites of wheat plants and, on sites suspected to have different food quality because of the presence/absence of meristems and therefore different nitrogen content, we evaluated pre-imaginal survival, nymphal developmental time, proportion of macropterous morphs, adult longevity and feeding rate.Delphacodes kuschelishowed a positive selection for plant zones suspected to have higher food quality and on them insects developed faster, exhibited higher nymphal survival and adult longevity and produced a lower proportion of macropterous morphs. Also on sites suspected to have lower food quality the number of honeydew droplets excreted per day increased and the mean diameter diminished, suggesting that the planthopper could probe more frequently to compensate for different food quality. [ABSTRACT FROM PUBLISHER]

The article describes the immatures of the South American plant hopper Taosa (C.) longula. It also provides a key for their identification for specimens collected on the water hyacinth Eichhornia crassipes. The immature stages of Taosa longula are described, as well as the physical characteristics of each nymph stages. Biological information on the plant hopper Taosa longula is also provided.

The bronze bug, Thaumastocoris peregrinus Carpintero & Dellapé, 2006 (Heteroptera: Thaumastocoridae) originally restricted to Australia, is an important emerging pest of Eucalyptus plantations in the Southern Hemisphere. It feeds on mature leaves, causing the loss of photosynthetic surface area and defoliation and, according to some studies, even tree death. In this work, feeding activities of T. peregrinus on Eucalyptus camaldulensis Dehn leaves and its primary food resources were identified. In cross sections of leaves, solid salivary deposits on epidermal cells and in the vicinity of stomata cells were detected. In subepidermal cells of the palisade parenchyma near the stylet penetration point, disorganization and removal of chloroplasts were also observed. The presence of chlorophyll in guts of adults and nymphs was analyzed using spectrophotometry and confocal laser scanning to obtain in situ fluorescent spectra. Both spectra showed chlorophyll absorbance peaks. In addition, the presence of chlorophyll in guts of T. peregrinus using fluorescence microscopy was identified. These results provide the first evidence that T. peregrinus feeds from the palisade parenchyma (chlorenchyma) of Eucalyptus leaves., (© The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)