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.

In this study, we surveyed the bacteriome-associated microbiota of the corn leafhopper Dalbulus maidis by means of histological, ultrastructural, and molecular analyses. Amplification and sequencing of 16S rDNA genes revealed that the endosymbiont "Candidatus Sulcia muelleri" (Phylum Bacteroidetes) resides in bacteriomes of D. maidis. Phylogenetic analysis showed that the sequence was closely allied to others found in representatives of the subfamily Deltocephalinae. We failed to amplify other sequences as "Candidatus Nasuia deltocephalinicola," a co-primary symbiont frequently associated to deltocephaline leafhoppers. In addition, a metagenetic analysis carried out in order to investigate the presence of other bacteriome-associated bacteria of D. maidis showed that the sequence of Sulcia accounted for 98.56 % of all the sequences. Histological and ultrastructural observations showed that microorganisms harbored in bacteriomes (central syncytium and cytoplasm of uninucleate bacteriocytes) look like others Sulcia described in hemipteran species and they were transovarially transmitted from mother to offspring which is typical of obligate endosymbionts. The only presence of Sulcia in the bacteriomes of D. maidis was discussed.

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) = KN o e rt /K+(e rt-1)N o , (N o = 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.