Leafhopper Dalbulus Maidis Research Articles

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.

Response of egg parasitoids (Hymenoptera: Mymaridae and Trichogrammatidae) to the density of Dalbulus maidis (Hemiptera: Cicadellidae) eggs in maize habitats

Understanding the response of egg parasitoids to host density is essential for efficient biological control. However, this response has been little investigated in parasitoids that attack eggs of insect pests that transmit plant pathogens in a persistent-propagative mode. The objective of the present study was to investigate the response of two egg parasitoid communities to high and low densities of eggs of the corn leafhopper Dalbulus maidis, an efficient vector of maize plant pathogens. Five and ten two-week-old female D. maidis (for the low-density and high-density groups, respectively) were allowed to oviposit on landrace maize leaves. The maize plants with the eggs were then transported to a seasonal and a year-round maize habitat in central Mexico, where they were exposed to naturally occurring parasitoids. In total, four treatments were conducted: seasonal maize habitat/low egg density (SL), seasonal maize habitat/high egg density (SH), year-round maize habitat/low egg density (YL), and year-round maize habitat/high egg density (YH). The parasitoids emerging from the eggs included the Mymaridae Anagrus virlai and Anagrus incarnatus, and the Trichogrammatidae Paracentrobia sp., Pseudoligosita sp., and Oligosita sp., with A. virlai as the most abundant species. An inverse density-dependent relationship was found between the number of D. maidis eggs and the rate of parasitism in the SH group. In the SL, YL, and YH groups, an independent relationship was seen between the number of eggs and the parasitism rate. These results suggest that high vs. low egg density affects the density-dependence relationships between egg parasitoids and their hosts.

Overwintering plants for Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae) adults during the maize off-season in central Brazil

Maize (Zea mays L.) is the only reproductive and feeding host plant of the corn leafhopper Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae) in Brazil and this insect is the only vector of the causal agents of corn stunting diseases in South America. The ability of D. maidis to survive on other plant species in the absence of their host plant is an area of speculation. This study observed the ability of D. maidis to use other plant species as overwintering or shelter plants during the maize off-season in central Brazil. This study was carried out in the Embrapa Cerrados (Planaltina/DF, Brazil) experimental field in August 2017, August 2018, and September 2018, during which maize plants were not present in the field. In these months, several plant species present in the field were sampled using an entomological net. Samples of D. maidis collected were sorted out in the laboratory, identified by sex, and counted. Twenty-nine plant species belonging to nine botanical families were sampled. In all, a total of 146 D. maidis adults were collected from 17 plant species which include, 64 in August 2017, 67 in August 2018, and 15 in September 2018. Approximately 93% of these collections were made on plants of the Poaceae family. The number of D. maidis females collected were higher than the number of males in all the sampling periods. This study therefore, suggest that during the maize off-season, part of the D. maidis population can survive and shelter on other plants of the Poaceae family.

Growth kinetic and nitrogen source optimization for liquid culture fermentation of Metarhizium robertsii blastospores and bioefficacy against the corn leafhopper Dalbulus maidis.

The cosmopolitan entomopathogenic and root endophytic fungus Metarhizium robertsii has a versatile lifestyle and during liquid fermentation undergoes a dimorphic transformation from hyphae to conidia or microsclerotia, or from hyphae to blastospores. In all cases, these processes are mediated by environmental and nutritional cues. Blastospores could be used in spray applications to control arthropod pests above ground and may serve as an attractive alternative to the traditional solid-grown aerial conidial spores of Metarhizium spp. found in commercial products. Nitrogen is a vital nutrient in cell metabolism and growth; however, it is the expensive component in liquid cultures of entomopathogenic fungi. Our goals in this study were to optimize nitrogen sources and titers for maximum production of M. robertsii blastospores cultured in shake flasks at highly aerated conditions and to furtherdetermine theirvirulence against the corn leafhopper Dalbulus maidis, an important vector of serious pathogens in maize crops worldwide. Our fermentation studies revealed that the low-cost corn steep liquor (CSL) was the most suitable nitrogen source to improve blastospore growth in M. robertsii. The growth kinetic assays determined the optimal titer of 80gL-1 and a yield up to 4.7 × 108 cells mL-1 within 5days of cultivation (3days preculture and 2days culture), at a total cost of US$0.30L-1. Moreover, the blastospore growth kinetic was strongly dependent on glucose and nitrogen consumptions accompanied by a slight drop in the culture pH. Insect bioassays evidenced a high virulence of these blastospores, either as dried or fresh cells, to D. maidis adults fed on maize plants. Our findings provide insights into the nutritional requirements for optimal and cost-efficient production of M. robertsii blastospores and elucidate the potential of blastospores as an ecofriendly tool against the corn leafhopper.

Molecular, Morphological, and Biological Differentiation between Anagrus virlai sp. n., an Egg Parasitoid of the Corn Leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) in the New World, and Anagrus incarnatus from the Palaearctic Region (Hymenoptera: Mymaridae)

The common New World egg parasitoid of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), an economically important pest of maize from Argentina to southern USA, has long been misidentified as the Palaearctic species Anagrus incarnatus Haliday or its synonym A. breviphragma Soyka (Hymenoptera: Mymaridae). Using a combination of genetic and morphometric methods, and available biological information, specimens reared from eggs of D. maidis in Argentina and Mexico, described and illustrated here as Anagrus (Anagrus) virlai Triapitsyn sp. n., are shown to be different from those of A. incarnatus from the Palaearctic region. Mitochondrial and nuclear ribosomal DNA sequence data provide clear evidence for the separation of the two species. Anagrus virlai is also known from Brazil, Colombia, Guadeloupe (France), and Guyana.

Do assortative mating and immigrant inviability help maintain population genetic structuring of an herbivore on a crop and a wild relative?

Population genetic structuring is common among herbivorous insects and frequently is associated with divergent host plants, such as crops and their wild relatives. Previous studies showed population genetic structuring in corn leafhopper Dalbulus maidis in Mexico, such that the species consists of two sympatric, host plant-associated populations: an abundant and widespread "pestiferous" population on maize (Zea mays mays), and a small and localized "wild" population on perennial teosinte (Zea diploperennis), a maize wild relative with a limited distribution. This study addressed whether assortative mating and immigrant inviability mediate genetic structuring of corn leafhopper by comparing the mating and reproductive successes of pestiferous and wild females that colonize their nonassociated host plants against the successes of females colonizing their associated host plants. Assortative mating was assessed by comparing mating frequencies and premating and mating times among females of each population on each host plant; immigrant inviability was assessed by comparing, across two generations, the fecundity, survival, development time, sex ratio, and population growth rate among leafhopper populations and host plants. Our results showed that on maize, and compared to resident, pestiferous females, wild females were more likely to mate, and greater proportions of their offspring survived to adult stage and were daughters; consequently, the per-generation population growth rate on maize was greater for immigrant, wild leafhoppers compared to resident, pestiferous leafhoppers. Our results suggested that wild leafhoppers emigrating to maize have a fitness advantage over resident, pestiferous leafhoppers, while immigrant pestiferous and resident wild leafhoppers on teosinte have similar fitnesses.

Bacteriomes of the corn leafhopper, Dalbulus maidis (DeLong & Wolcott, 1923) (Insecta, Hemiptera, Cicadellidae: Deltocephalinae) harbor Sulcia symbiont: molecular characterization, ultrastructure, and transovarial transmission

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.

Innate and Learned Prey-Searching Behavior in a Generalist Predator.

Early colonization by Zyginidia scutellaris leafhoppers might be a key factor in the attraction and settling of generalist predators, such as Orius spp., in maize fields. In this paper, we aimed to determine whether our observations of early season increases in field populations of Orius spp. reflect a specific attraction to Z. scutellaris-induced maize volatiles, and how the responses of Orius predators to herbivore-induced volatiles (HIPVs) might be affected by previous experiences on plants infested by herbivorous prey. Therefore, we examined the innate and learned preferences of Orius majusculus toward volatiles from maize plants attacked by three potential herbivores with different feeding strategies: the leafhopper Z. scutellaris (mesophyll feeder), the lepidopteran Spodoptera littoralis (chewer), and another leafhopper Dalbulus maidis (phloem feeder). In addition, we examined the volatile profiles emitted by maize plants infested by the three herbivores. Our results show that predators exhibit a strong innate attraction to volatiles from maize plants infested with Z. scutellaris or S. littoralis. Previous predation experience in the presence of HIPVs influences the predator's odor preferences. The innate preference for plants with cell or tissue damage may be explained by these plants releasing far more volatiles than plants infested by the phloem-sucking D. maidis. However, a predation experience on D. maidis-infested plants increased the preference for D. maidis-induced maize volatiles. After O. majusculus experienced L3-L4 larvae (too large to serve as prey) on S. littoralis-infested plants, they showed reduced attraction toward these plants and an increased attraction toward D. maidis-infested plants. When offered young larvae of S. littoralis, which are more suitable prey, preference toward HIPVs was similar to that of naive individuals. The HIPVs from plants infested by herbivores with distinctly different feeding strategies showed distinguishable quantitative differences in (Z)-3-hexenal, (E)-2-hexenal, and methyl salicylate. These compounds might serve as reliable indicators of prey presence and identity for the predator. Our results support the idea that feeding by Z. scutellaris results in the emission of maize's HIPVs that initially recruit Orius spp. into maize fields.

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.

Simultaneous transmission of phytoplasma and spiroplasma byDalbulus maidisleafhopper and symptoms of infected maize

Two experiments were carried out to study simultaneous transmission of phytoplasmas and spiroplasmas by the leafhopper Dalbulus maidis from double infected popcorn-plants. The double infection was obtained through only one leafhopper from field per plant. The results indicated variability among isolates and combinations of phytoplasmas and spiroplasmas for transmission by D. maidis and maize leaf symptoms expression.

Quantitative trait loci for resistance to Maize rayado fino virus

Maize rayado fino virus (MRFV) causes one of the most important virus diseases of maize in regions of Mexico, Central and South America, where it causes moderate to severe yield losses. The virus is found from the southern USA to northern Argentina where its vector, the maize leafhopper Dalbulus maidis, is present. Although resistance to MRFV has been identified in tropical maize lines, little was known about genes or quantitative trait locus (QTL) conferring resistance to MRFV. In order to identify the location of genes conferring resistance to MRFV, two recombinant inbred line mapping populations that segregated for MRFV resistance were inoculated using viruliferous leafhoppers, and their responses to virus inoculation were evaluated under greenhouse conditions 7, 14 and 21 days post inoculation. A QTL explaining up to 23 % of the total phenotypic variance was mapped on chromosome 10 in both populations, with similar genetic and physical positions identified in the two populations. The magnitude of the QTL effect and the validation in two independent populations suggests that resistance to MFRV could be transferred into elite breeding lines to develop resistant cultivars.

Is There any Genetic Variation among Native Mexican and Argentinian Populations ofDalbulus maidis(Hemiptera: Cicadellidae)?

ABSTRACT The corn leafhopper Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae) originated in Mexico, but is found from southeastern and southwestern USA to Argentina. Differences in reproductive and phenotypic traits between Mexican (native) and Argentinian (adventive) populations have been previously reported, but information on their genetic variation is currently unavailable. The objective was to investigate possible genetic variability among D. maidis populations collected in Mexico on maize and maize relatives (annual and perennial teosintes) and on maize in Argentina. A region of the mitochondrial gene coding for the cytochrome oxidase subunit I (mtCOI) and the ribosomal internal transcribed spacer (ITS2) were sequenced and analyzed. We developed the forward and reverse primers for the DNA amplification of COI in D. maidis (dalCOI). Twenty two and 17 sequences for dalCOI and ITS2, respectively, were generated and analyzed. No genetic variation among Mexican and Argentinian populations was...

Exitianus obscurinervis (Hemiptera: Cicadellidae), a New Experimental Vector of Spiroplasma kunkelii

"Corn stunt" caused by the mollicute Spiroplasma kunkelii (Whitcomb) is potentially one of the most severe diseases affecting the corn (Zea mays L.) crop in the Americas, and the leafhopper Dalbulus maidis (DeLong & Wolcott) is considered its most important vector. However, other insects seen quite frequently in corn crops might well be its vectors in Argentina To identify any leafhoppers species other than D. maidis that can transmit S. kunkelii, transmission assays were conducted, using individuals of Exitianus obscurinervis (Stål) collected in field and reared under controlled conditions. S. kunkelii was transmitted to corn plants by E. obscurinervis. The pathogen was transmitted to seven of the 11 plants, which showed characteristic corn stunt symptoms, and the presence of the pathogen was confirmed by DAS-ELISA. The presence of S. kunkelii in the E. obscurinervis individuals used in transmission experiments was confirmed by polymerase chain reaction and electron microscopy. The current study shows the existence of a new experimental vector of S. kunkelii, the leafhopper E. obscurinervis, which acquired spiroplasmas from infected plants and inoculated it to healthy plants.

First host record for Anteon pilicorne (Ogloblin) (Hymenoptera: Dryinidae), a parasitoid of Cicadellidae, including the corn leafhopper (Hemiptera: Cicadellidae)

For the first time the dryinid wasp Anteon pilicorne (Ogloblin) is recorded as a parasitoid of two Macrostelini leafhoppers: Balclutha rosea (Scott) and the corn leafhopper Dalbulus maidis (DeLong & Wolcott). New distributional records are 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

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.

Effects of Corn Stunt Spiroplasma on Survival of <I>Dalbulus maidis</I> (Hemiptera: Cicadellidae) Parasitized or Preyed upon by <I>Gonatopus bartletti</I> (Hymenoptera: Dryinidae) or Infected by <I>Metarhizium anisopliae</I>

The effects of corn stunt spiroplasma (CSS), Spiroplasma kunkelii, on survival of corn leafhopper Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae), exposed to parasitism, fungal disease, or predation were investigated in the laboratory. Adult corn leafhoppers with or without CSS were exposed separately to parasitism or predation by Gonatopus bartletti, a parasitoid that acts also as a predator, or to infection by Metarhizium anisopliae, a pathogenic fungus, to evaluate the effects of CSS on corn leafhopper survival confronted with these natural enemies. CSS alone did not affect corn leafhopper survival, but differentially mediated survival of leafhoppers exposed to parasitism or predation by G. bartletti, or infection with M. anisopliae. CSS did not affect the survival of corn leafhoppers parasitized by G. bartletti: Survivorship of leafhoppers carrying CSS and parasitized by G. bartletti was ≈9%, whereas in the absence of CSS and parasitized it was ≈17%, but the difference was not significant. Similarly, CSS did not affect the survival of corn leafhoppers infected with M. anisopliae: Survivorship of leafhoppers carrying CSS and infected with M. anisopliae was ≈64%, whereas in the absence of CSS and infected with M. anisopliae it was ≈73%, but the difference was not significant. In contrast, CSS reduced the survival rate of corn leafhoppers exposed to predation by G. bartletti, though the effect was mediated by the incubation period of CSS. Corn leafhoppers exposed to predation and carrying CSS for 10 or 20 d had significantly lower survivorship rates, ≈54 and ≈47%, respectively, compared with those of leafhoppers carrying CSS for 2 d or free of CSS, ≈91 and ≈78%, respectively. The lower survival rate of corn leafhoppers carrying CSS and exposed to predation by G. bartletti, particularly of leafhoppers with longer CSS incubation periods, together with the lower survival rate of CSS in leafhoppers parasitized by G. bartletti documented in earlier studies, are suggested as factors limiting the abundance of the vector and plant pathogen in their shared area of origin.

Habitat of the Corn Leafhopper (Hemiptera: Cicadellidae) During the Dry (Winter) Season in Mexico

Although the corn leafhopper Dalbulus maidis (DeLong and Wolcott) is the most important vector of maize pathogens in Latin America, little is known about how and where it overwinters (passes the dry season), particularly in Mexico. The objectives of this study were (1) to monitor the abundance of D. maidis adults throughout the dry season in maize and maize-free habitats and (2) to determine where and how D. maidis adults, exposed or nonexposed to the maize pathogen Spiroplasma kunkelii Whitcomb, overwinter in a maize-free habitat. Work for the first objective was done during the two consecutive dry seasons of 1999-2000 and 2000-2001; the second objective was done during the dry seasons of 2003-2004 and 2005-2006. During the dry winter seasons, D. maidis was prevalent as long as maize was present in irrigated areas. The leafhopper was found in 52 of the 58 irrigated maize fields sampled in Mexico at the end of the dry seasons of 1999-2000 and 2000-2001. However, leafhopper adults were not found in nonirrigated maize-free habitats at high elevation during the dry winter season (February, March, and April), although leafhopper adults were prevalent on perennial wild grasses in January after maize harvest. Additional experiments revealed, however, that corn leafhopper adults, although few in number, survived the entire dry season in these nonirrigated maize-free fields. Also, no detectable difference in survival existed between leafhoppers exposed and those not exposed to S. kunkelli during the two dry seasons in the maize-free habitat.

Field overwintering biology of Spiroplasma kunkelii (Mycoplasmatales: Spiroplasmataceae) and its vector Dalbulus maidis (Hemiptera: Cicadellidae)

AbstractWe studied the corn stunt spiroplasma (CSS), Spiroplasma kunkelii (Mycoplasmatales: Spiroplasmataceae) and its vector the corn leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) under field conditions in Mexico. We surveyed for the presence of CSS in D. maidis by using PCR on samples of adults collected during the 2000–01 and 2003–04 winter (dry) seasons from irrigated low‐elevation sites and un‐irrigated high‐elevation sites. Also, we determined the body size and number of mature eggs of D. maidis females collected during the dry season in 2004 and in females collected on maize seedlings in the first months (June and July) of the wet (summer) season in 2005. Our PCR results showed that CSS was present in leafhopper adults collected during the 2000–01 and 2003–04 dry seasons in irrigated low‐elevation sites. However, in un‐irrigated high‐elevation sites, CSS was present in corn leafhopper adults caught before, but not during, the dry seasons. In these un‐irrigated high‐elevation sites, adult leafhoppers without CSS were recovered during the first 2 months (November and December) of the dry season from the foliage of wild perennial grasses. Females collected on wild perennial grasses in December 2004 showed similar head width and wing length to females caught on maize seedlings in June 2005. However, females collected on maize seedlings in July 2005 had the widest heads, longest wings and highest number of mature eggs. The largest body size of these females that arrived in July 2005 indicates that they are immigrants and support the Roff’s hypothesis that insect migrants should be larger than nonmigrants.

Influence of Latitude and Elevation on Polymorphism Among Populations of the Corn Leafhopper,Dalbulus maidis(DeLong and Wolcott) (Hemiptera: Cicadellidae), in Brazil

Morphological variations in insects have been shown to be influenced by latitude and elevation. Here we show that these two parameters markedly influence the appearance of the corn leafhopper Dalbulus maidis (DeLong and Wolcott). Leafhopper samples were collected in maize from 27 localities in 10 Brazilian states, with latitudes from 5 to 28° S and elevations from 16 to 1,628 m. D. maidis was the only Dalbulus species found in the samples. Up to 10 males and 10 females of D. maidis from each collection site were evaluated for size, pigmentation, and body weight. Females were always bigger and heavier than the males in the same locality. For both sexes, there was a positive and significant correlation between the morphological variables measured and the latitude and elevation from where specimens were collected. Individuals from higher latitudes (southern region) were bigger, darker, and heavier than those from lower latitudes (northeastern region). There was also a tendency for an increase in body weight, head capsule width, and wing length at higher elevations.

Infection and replication sites of Spiroplasma kunkelii (Class: Mollicutes) in midgut and Malpighian tubules of the leafhopper Dalbulus maidis.

Spiroplasma kunkelii distribution and infection mechanisms in the intestines and Malpighian tubules of Dalbulus maidis were investigated by transmission electron microscopy. Spiroplasmas were found between microvilli and in endocytic vesicles of the midgut epithelium. At the basal part, cytoplasmic vesicles contained multiple spiroplasmas with tube-like extensions and spiroplasmas accumulated between the laminae rara and densa of the basal lamina. Tip structures of flask-shaped spiroplasmas pierced the lamina densa that was discontinuous in close proximity to spiroplasmas. Spiroplasmas were found in hemolymph, crossed the basal lamina of Malpighian tubule epithelium and accumulated at high numbers in muscle cells that had cytopathogenic changes. S. kunkelii had perithrochous approximately 8nm diameter structures determined to be fimbriae protruding from the cell surface, and similar structures were adhering to the basal lamina of midgut epithelium and to external lamina of muscle cells. Further, spiroplasmas had pili-like appendages at one or both cell poles and appeared to conjugate. This is the first time that fimbriae and pili have been observed in a mollicutes.