María Eugenia Brentassi

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.

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.

Diversity of leafhoppers (Hemiptera: Cicadellidae) in experimental rice lots and associated weeds in Buenos Aires province, Argentina

We identified the species of Cicadellidae associated with rice fields from an agricultural experimental station of La Plata city, Argentina, and explored the diversity pattern of the leafhopper assemblage. Insects were obtained from rice and surrounding weeds between 2006 and 2010. Syncharina argentina (Berg) and Agalliana ensigera Oman were the most abundant species in rice and weeds, respectively. Diversity (H′), heterogeneity (D) and evenness (J) indices were estimated. There was a significant effect of crop cycle (2006 to 2010) and host plant (rice and weeds) on H′ and D, with the interaction between them being not significant. Evenness was similar in rice lots and weeds, but differed between crop cycles. The pattern of abundance of species within rice lots and weeds followed the logarithmic model. Possible explanations for this pattern are discussed. The importance of the presence of some species as vectors of plant pathogens is highlighted.

Phenotypic plasticity of the planthopper Delphacodes kuscheli (Hemiptera: Delphacidae) revealed by its selectivity, feeding rate and demographic traits on different food quality sites of wheat plants

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 kuscheli showed 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.

Diversity of planthoppers (Hemiptera: Fulgoromorpha) in rice associated with weeds in Argentina

An assemblage of Fulgoromorpha in a rice agroecosystem from La Plata city was studied for the first time in Argentina, considering those species associated with rice and the surrounding weeds, their seasonality, sex ratios and parasitoidism. Samples were obtained from 2006 to 2010 in a rice field and in the surrounding weeds. Fourteen species from three families of Fulgoromorpha were associated with rice, most of them native species. The delphacids Chionomus haywardi, Toya propinqua and Delphacodes kuscheli were the most abundant on rice. Population peaks occurred after flooding of rice and before anthesis. The native C. haywardi was more abundant in rice than in weeds, while the opposite was confirmed for T. propinqua, a well-known cosmopolitan grass specialist. The difference of abundances of D. kuscheli in rice and weeds was not significant. Our results highlight the dominance of C. haywardi during all sampling years in the rice agroecosystem as well as the role of surrounding weeds as an alternative microhabitat for planthoppers instead of rice. The strepsipteran Elenchus tenuicornis was the only recorded parasitoid and showed no preference for any of the insect hosts.

Descriptions of Immatures of the South American Plant Hopper, Taosa (C.) longula

Abstract Descriptions of the immature stages of Taosa (Cuernavaca) longula Remes Lenicov (Hemiptera: Fulgoroidea: Dictyopharidae) and a key for their identification is provided for specimens collected on the water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Commelinales: Pontederiaceae), in northeastern Argentina and Peru. Newly emerged nymphs from eggs collected in the field were reared in rearing chambers, and each stage was fixed to microscopic examination and illustration. Fifth nymphal instars can be easily recognized from congeners by the brown marked pattern coloration, shorter vertex, and the distinguishable median carina along the frons. Information on behavior and developmental time is also included.

First Record of the Genus Zygina from a Neotropical Region on Populus spp.: Taxonomic and Biological Characteristics

Abstract The typhlocybine, Zygina nivea Mulsant & Rey 1855, was found in urban areas of Argentina colonizing trees of poplar (Populus alba L. and P. nigra L.). This is the first mention of the genus Zygina Fieber from the Neotropical region. In this paper redescription of the male, description of the female, distributional and host plant data, and behavioural observations of this species are given.

Food quality affects wing-form, demographic traits and number of yeast-like symbionts (YLS) in the planthopper vector, Delphacodes kuscheli (Hemiptera: Delphacidae)

ABSTRACT 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.