Corn Leafhopper Research Articles

Bottom-up effect of nitrogen fertilization on the density of the corn leafhopper and its impact on both disease incidence and natural parasitism

Bottom-up effect of nitrogen fertilization on the density of the corn leafhopper and its impact on both disease incidence and natural parasitism

First Report of a Mastrevirus (Geminiviridae) Transmitted by the Corn Leafhopper.

Maize striate mosaic virus (MSMV; genus Mastrevirus) was recently reported in maize plants in Brazil and also detected by metagenomic analyses in the corn leafhopper, Dalbulus maidis (DeLong & Wolcott). Although these findings suggested that D. maidis is a potential vector, no transmission studies have been performed. Here, we tested the transmission of MSMV by D. maidis from field-collected infected plants and plants infected with MSMV via leafhopper-mediated transmission in the laboratory; all plants were confirmed positive for MSMV by PCR. In each one of three transmission replicates, aviruliferous D. maidis nymphs and adults were confined together on a source plant during a 4-day acquisition access period (AAP) and subsequently transferred to healthy maize seedlings (10 individuals per test plant) in a series of 4-day inoculation access periods (IAPs). We also tested transmission by the corn aphid, Rhopalosiphum maidis (Fitch) and by mechanical inoculation of healthy maize seedlings. Only D. maidis transmitted MSMV, with overall transmission rates of 29.4 and 39.5% on field-collected infected plants and 18.5% on infected plants in laboratory. D. maidis transmitted MSMV until the third (8 to 12 days after the AAP) or fourth successive IAP (12 to 16 days), with gradual loss in transmission efficiency and rate of viruliferous insects over time, suggesting a persistent but nonpropagative mode of transmission. Infected test plants showed mottling symptoms with mild chlorotic streaks and height reduction. This is the first report of transmission of a mastrevirus by D. maidis, facilitating the completion of Koch's postulate for MSMV.

Insecticide seed treatment against corn leafhopper: helping protect grain yield in critical plant growth stages.

The corn leafhopper, Dalbulus maidis (Hemiptera: Cicadellidae), spreads maize stunt pathogens and requires timely and effective crop protection. We determined the interaction between maize phenology and the vector feeding/infection period by stunt pathogens with the residual efficacy of neonicotinoid insecticidal seed treatments. Greenhouse- and field-grown maize plants, seed-treated with clothianidin or imidacloprid insecticides, were infested during seven growth stages with corn leafhoppers reared under controlled conditions on maize plants displaying infection symptoms by both spiroplasma (corn stunt spiroplasma, Spiroplasma kunkelii) and phytoplasma (maize bushy phytoplasma) pathogens. In the greenhouse and field settings, seed treatment reduced the stunt disease symptoms and corn yield loss during the VE-V4 maize growth stages and caused no phytotoxicity. The neonicotinoid seed treatment reduced 20-60% of the yield losses from the corn stunt disease until the V4 growth stage. Infestation by infective corn leafhoppers in the V12 maize growth stage caused a 25-30% yield loss irrespective of seed treatment, yet no stunt disease symptom was evident. Nonetheless, corn yield losses and visual stunt symptoms as rated by a nine-category ordinal scale were strongly correlated (r=0.79, P < 0.01). These results reinforce that maize plants are more susceptible to leafhopper stunt disease during the VE-V4 growth stages (emergence to the fourth-leaf stage). Seed treatment helps reduce the damage in the early growth stages (VE-V2), although supplemental control measures depending on leafhopper population density may be needed from VE-V12 to protect yield losses from the maize stunt condition. © 2021 Society of Chemical Industry.

Re-Emergence of Corn Leafhopper (Dalbulus maidis; Hemiptera: Cicadellidae), an Exotic and Invasive Pest of Maize in South Texas

Corn leafhopper, Dalbulus maidis (DeLong and Wolcott), can negatively impact production of maize (Zea mays L.) through direct damage while feeding and possible transmission of three plant pathogens. We present evidence of reemergence of D. maidis on maize in South Texas during the summer of 2016. Insect specimens resembling the exotic and invasive pest were collected in surveys at an experimental plot and a commercial field of maize in South Texas. Morphological and molecular taxonomy were used to validate identity of the species.

Eight Decades of Dalbulus maidis (DeLong & Wolcott) (Hemiptera, Cicadellidae) in Brazil: What We Know and What We Need to Know.

The corn leafhopper Dalbulus maidis (DeLong & Wolcott) is one of the most important maize (Zea mays L.) pests in Latin America because of its ability to efficiently transmit pathogens [maize bushy stunt phytoplasma (MBSP) and corn stunt spiroplasma-Spiroplasma kunkelli Whitcomb et al. (CSS)] associated with corn stunt disease complex and maize rayado fino virus (MRFV). This leafhopper species, considered a secondary pest until a few years ago, was first reported in Brazil in 1938. Since 2015, corn stunt diseases have been the main phytosanitary threat to corn production in Brazil, and D. maidis has assumed the status of a key pest of the crop. In this study, we gathered pertinent information about the corn leafhopper, from the time it was first recorded in Brazil. Aspects such as origin, association with maize, bioecology, geographical distribution in the Americas, and its congeners are addressed. We present a history of studies performed with this species in the country, its importance as a pest, host plants, and survival strategies during the maize off-season. Based on the available scientific knowledge, the main management strategies for insect vectors and diseases are discussed. Finally, the main knowledge gaps for this insect vector and the prospects for future studies and actions to mitigate the damage caused by insect vectors in maize crops in Brazil are presented and discussed.

Transcriptome of the Maize Leafhopper (Dalbulus maidis) and Its Transcriptional Response to Maize Rayado Fino Virus (MRFV), Which It Transmits in a Persistent, Propagative Manner.

ABSTRACTThe corn leafhopper (Dalbulus maidis) is an important vector of maize rayado fino virus (MRFV), a positive-strand RNA (+ssRNA) marafivirus which it transmits in a persistent propagative manner. The interaction of D. maidis with MRFV, including infection of the insect and subsequent transmission to new plants, is not well understood at the molecular level. To examine the leafhopper-virus interaction, a D. maidis transcriptome was assembled and differences in transcript abundance between virus-exposed and naive D. maidis were examined at two time points (4 h and 7 days) post exposure to MRFV. The D. maidis transcriptome contained 56,116 transcripts generated from 1,727,369,026 100-nt paired-end reads from whole adult insects. The transcriptome of D. maidis shared highest identity and most orthologs with the leafhopper Graminella nigrifrons (65% of transcripts had matches with E values of <10−5) versus planthoppers Sogatella furcifera (with 23% of transcript matches below the E value cutoff) and Peregrinus maidis (with 21% transcript matches below the E value cutoff), as expected based on taxonomy. D. maidis expressed genes in the Toll, Imd, and Jak/Stat insect immune signaling pathways, RNA interference (RNAi) pathway genes, prophenoloxidase-activating system pathways, and immune recognition protein-encoding genes such as peptidoglycan recognition proteins (PGRPs), antimicrobial peptides, and other effectors. Statistical analysis (performed by R package DESeq2) identified 72 transcripts at 4 h and 67 at 7 days that were significantly responsive to MRFV exposure. Genes expected to be favorable for virus propagation, such as protein synthesis-related genes and genes encoding superoxide dismutase, were significantly upregulated after MRFV exposure.IMPORTANCE The transcriptome of the corn leafhopper, D. maidis, revealed conserved biochemical pathways for immunity and discovered transcripts responsive to MRFV-infected plants at two time points, providing a basis for functional identification of genes that either limit or promote the virus-vector interaction. Compared to other hopper species and the propagative plant viruses they transmit, D. maidis shared 15 responsive transcripts with S. furcifera (to southern rice black-streaked dwarf virus [SRBSDV]), one with G. nigrifrons (to maize fine streak virus [MFSV]), and one with P. maidis (to maize mosaic virus [MMV]), but no virus-responsive transcripts identified were shared among all four hopper vector species.

Development of novel spray-dried and air-dried formulations of Metarhizium robertsii blastospores and their virulence against Dalbulus maidis.

The present research addressed spray-drying and air-drying techniques applied to Metarhizium robertsii blastospores to develop wettable powder (WP) formulations. We investigated the effect of co-formulants on blastospore viability during drying and assessed the wettability and stability of formulations in water. The effect of oxygen-moisture absorbers was studied on the shelf life of these formulations stored at 26°C and 4°C for up to 90days. Additionally, we determined the virulence of the best spray-dried and air-dried formulations against the corn leafhopper Dalbulus maidis. While sucrose and skim milk played an essential role as osmoprotectants in preserving air-dried blastospores, maltodextrin, skim milk, and bentonite were crucial to attain high cell survival during spray drying. The lowest wettability time was achieved with spray-dried formulations containing less Ca-lignin, while charcoal powder amount was positively associated with formulation stability. The addition of oxygen-moisture absorbers inside sealed packages increased from threefold to fourfold the half-life times of air-dried and spray-dried formulations at both storage temperatures. However, the half-life times of all blastospore-based formulations were shorter than 3months regardless of temperature and packaging system. Spray-dried and air-dried WP formulations were as virulent as fresh blastopores against D. maydis adults sprayed with 5 × 107 blastospores mL-1 that induced 87.8% and 70.6% mortality, respectively. These findings bring innovative advancement for M. robertsii blastospore formulation through spray-drying and underpin the importance of adding protective matrices coupled to oxygen-moisture absorbers to extend cell viability during either cold or non-refrigerated storage. KEY POINTS: • Cost-effective wettable powder formulations of M. robertsii blastospores were developed. • Bioefficacy of formulations against the corn leafhopper was comparable to fresh blastospores. • Cold storage and dual oxygen-moisture absorber are critical for extended shelf life.

First report on the natural occurrence of entomopathogenic fungi in populations of the leafhopper Dalbulus maidis (Hemiptera: Cicadellidae): Pathogen identifications and their incidence in maize crops

The corn leafhopper Dalbulus maidis is one of the most important pests of maize in Latin America. Here we report, for the first time, the natural occurrence of two fungal species infecting the adult stage of this pest. In 2020, insects killed by a pale bluish green fungus in irrigated maize fields located in Northeast Brazil were found attached to the abaxial surface of leaves. Using morphological characters and multigenic phylogeny, it was identified as Metarhizium brasiliense. In the beginning of 2021, the same pathogen was seen on adults in a maize field in the Central-Western region, alongside an entomophthoralean fungus during an epizootic. The latter pathogen was molecularly identified as a species in the genus Batkoa. The number of Batkoa-infected leafhoppers, displaying the typical swollen abdomen and extended wings, reached an average of 1.88 per maize leaf (86.42% of the sampled adults). The incidence of M. brasiliense was higher in plots in the Northeastern region (0.22 and 0.53 adult per leaf) when compared to the Central-Western region (0.04 adult per leaf). The report of D. maidis adults infected by M. brasiliense in agricultural settings located in different geographic regions and over 550 km apart indicates probable widespread occurrence of this pathogen in Brazil. Moreover, this opens the possibility of more applied biological control studies and, perhaps, the development of new tools to manage D. maidis populations.

Morphological variation of the parasitic wasp Paracentrobia subflava (Hymenoptera: Trichogrammatidae) emerged from different leafhopper species

The parasitic wasp Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae) develops within the eggs of the corn leafhopper Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), one of the most important pests in maize throughout the Americas. The aim of the present study was to determine whether variation occurs in female and male body size and male genitalia of P. subflava emerged from eggs of D. maidis and two other host species: Dalbulus elimatus (Ball), and Dalbulus quinquenotatus (DeLong and Nault), representing different species groups within the genus. Body variation of the emerged adult parasitoids was evaluated using traditional morphometrics and male genitalia shape variation was assessed using geometric morphometrics. Female parasitoids emerged from D. elimatus eggs had significantly larger hind tibiae, wings and ovipositor. Most antennal variables also exhibited significant differences in females emerged from D. elimatus. In contrast, little differentiation was found among parasitoid males emerged from the different Dalbulus hosts. Accordingly, shape of male genitalia was similar when P. subflava developed in each of the three Dalbulus host eggs. Egg size differs among the examined Dalbulus species, but does not seem to be associated with patterns of variation in parasitoid size. Implications of this morphological variation for parasitoid identification and its relationship with host egg size and structure are discussed.

Variable levels of antibiosis and/or antixenosis of Bt and non-Bt maize genotypes on Dalbulus maidis (Hemiptera: Cicadellidae)

The corn leafhopper Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) poses a serious threat to the crop, causing direct and indirect damage to plants. The present study aimed to investigate the possible expression of resistance by antixenosis and/or antibiosis against D. maidis in 11 corn genotypes [8 non-Bt (60XB14, 90XB06, XB 9003, XB 8018, XB 8010, IAC 8390, IAC 8046, and IAC AIRAN) and 3 Bt (XB 7116 Bt, XB 8010 Bt, and DKB 310 Bt)] previously selected in a greenhouse. Initially, no choice preference tests for oviposition were performed to characterize the expression of antixenosis. To characterize the expression of antibiosis/antixenosis, the insects were confined to leaves of different genotypes to assess the following parameters: duration of each nymphal stage, nymphal period, viability per instar, total viability, and adult longevity. Additionally, morphological and physical analyses of the genotypes were carried out to establish correlations with the resistance categories. The genotypes 90XB06, IAC 8390, XB 9003 and DKB 310 PRO3 expressed antixenosis against leafhoppers, reducing insect oviposition. The genotypes 60XB14, 90XB06, IAC 8046, XB 8018 and IAC 8390 expressed antibiosis and/or antixenosis against leafhoppers, reducing nymphal viability. The hardness of the ribs is probably associated with the resistance of some of the evaluated genotypes and is an important morphological defense against leafhoppers. The results of this study are novel and can aid in corn-breeding programs focused on plant resistance to sucking insects, with relevant impacts on the integrated pest management of the crop.

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.

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.

Influence of adult diet on fitness and reproductive traits of the egg parasitoid Anagrus virlai (Hymenoptera: Mymaridae), a potential biocontrol agent against the corn leafhopper

AbstractDalbulus maidis is the most important leafhopper pest of maize in the Americas. Anagrus virlai is an egg parasitoid commonly associated with the corn leafhopper. We evaluated whether the performance of A. virlai is dependent on different diets provided during 24 hr or throughout adult female lifetime. Additionally, functional response of A. virlai on D. maidis eggs using maize leaves containing honeydew plus honey was described. A. virlai is a mostly pro‐ovigenic autogenic species whose females are able to parasitize eggs immediately after emergence. We found that wasps oviposit the majority of their eggs in the first day of their adult life. Realized lifetime fecundity and lifetime potential fecundity did not differ significantly among treatments, but longevity and egg production increased when honey was added to diet. Data were consistent with an intermediate functional response between type II and III, but closer to type II, indicating a high parasitism rate at low host densities and a decrease in the oviposition rate at high host densities, due to a possible egg limitation. Our results suggest that carbohydrate food sources (honeydew and honey) might not be the factor limiting reproductive success during the first 24 hr. Food supply, however, might influence egg maturation and survivorship of wasps, thus potentially enhancing biological pest control when hosts are scarce in the course of the first few days of adulthood.

Differential transmission of phytoplasma and spiroplasma to maize caused by variation in the environmental temperature in Brazil

The effects of temperature in winter-spring (average 17.0 °C) and spring-summer (average 23.0 °C) seasons on the transmission and latent period of maize bushy stunt phytoplasma (MBS-phytoplasma) and corn stunt spiroplasma (CSS) (Spiroplasma kunkelii) caused by the corn leafhopper, Dalbulus maidis (DeLog and Wolcott) (Hemiptera: Cicadellidae) were evaluated in two experiments in a screenhouse in Sete Lagoas, Minas Gerais State, Brazil. Approximately 200 mollicute-free adults of D. maidis were confined on popcorn (Zea mays L. cv. IAC125) plants infected with spiroplasma and the same number of mollicute-free leafhoppers were confined on plants infected with phytoplasma. They remained on the source plants for a 6 d acquisition access period (AAP). Next, leafhoppers were fed healthy popcorn seedlings. Transmission tests were performed with one leafhopper per seedling for each mollicute, with 12 replicates, at 12, 20, 30, 40 d since the first day of AAP. In addition, at 40 d, one leafhopper with phytoplasma and another with spiroplasma were confined together on 24 popcorn seedlings. The inoculation access period (IAP) was 3 d. The temperature was recorded daily during the experimental periods. In Experiment 1, during the 40 d latent period, only 41.6% and 58.3% of plants, respectively, exposed to phytoplasma or to both mollicutes presented MBS-phytoplasma symptoms. In Experiment 2, during the 20 d latent period, some popcorn plants presented MBS-phytoplasma (16.7%) and CSS (33.3%) symptoms, whereas almost 100% of plants at the 30 and 40 d latent period presented disease symptoms. Plant symptoms and results from PCR tests indicated that MBS-phytoplasma was more tolerant to low temperatures than S. kunkelii.

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.

Assessing the impact of climate change on the worldwide distribution of Dalbulus maidis (DeLong) using MaxEnt.

For the first time, a model was applied at the global scale to investigate the effects of climate change on Dalbulus maidis. D. maidis is the main vector of three plant pathogens of maize crops and has been reported as one of the most important maize pests in Latin America. We modelled the effects of climate change on this pest using three Global Climate Models under two Representative Concentration Pathways (RCPs) using MaxEnt software. Overall, climate change will lead to a decrease in suitable areas for D. maidis. In South America, climate change will decrease the areas suitable for the pest, especially in Brazil. However, Argentina, Chile, Colombia, Ecuador, Peru and Venezuela will have small areas that are highly suitable for the corn leafhopper. Outside the pest's range, Ethiopia, Kenya, Rwanda, Burundi and South Africa also should be concerned about the risk of corn leafhopper invasions in the future because they are projected to have conditions that are highly suitable for this insect in some areas. This study allows the relevant countries to increase their quarantine measures and guide researchers to develop new Zea mays varieties that are resistant or tolerant to D. maidis. In addition, the maize-stunting pathogens for the areas are highlighted in this modelling. © 2019 Society of Chemical Industry.

Egg Parasitoids of Dalbulus maidis (Hemiptera: Cicadellidae) Within Maize Agroecosystems and in the Edge Zones of Maize Fields, and on Maize Varieties During the Wet Season in Mexico.

Little is known about Dalbulus maidis (DeLong) egg parasitoids within maize fields, in the edge zones that surround these fields, and the parasitism on D. maidis eggs oviposited on different maize varieties. The objectives of the present study were first to understand which egg parasitoid species attack D. maidis eggs within maize fields and in the surrounding edge zones, and second, to compare parasitism on two maize varieties (land race Ancho-pozolero and hybrid Tigre-Asgrow) during the maize-growing wet season. We used maize plants with sentinel eggs to attract the egg parasitoids in two consecutive wet seasons, in 2015 and 2016. In 2015, Anagrus sp. (Hymenoptera: Mymaridae) and Paracentrobia sp. (Hymenoptera: Trichogrammatidae) parasitized D. maidis eggs within the maize field and on its edges. However, much more parasitism was seen within the maize agroecosystem than in the maize edge zones. In 2016, two Mymaridae species, Anagrus columbi Perkins and Anagrus sp, and two Trichogrammatidae genera, Pseudoligosita sp. and Paracentrobia sp., attacked the D. maidis eggs laid on maize hybrids but not those oviposited on the maize land race. Our findings indicate that parasitism of corn leafhopper eggs differs with agroecosystem location and maize varieties.

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.