Optimizing Corn Crop Protection: The First Sampling Plan for Controlling Dalbulus maidis (Hemiptera: Cicadellidae).

Corn (Zea mays) is the most widely planted crop in the world. Dalbulus maidis (Hemiptera: Cicadellidae) is currently a primary corn pest. The starting point for the development of pest control decision-making systems is the determination of a conventional sampling plan. Therefore, this study aimed to determine a practical conventional sampling plan for D. maidis in corn crops. Insect density was evaluated in 28 commercial fields. Subsequently, D. maidis densities were sampled from fields ranging from 1 to 100 ha. Insect density conformed to a negative binomial distribution in 89.29% of the fields. The insect densities determined using the sampling plan had a low error rate (up to 15%). Sampling time and costs ranged from 2.06 to 39.45 min/ha and 0.09 to 1.81 USD/ha for fields of 1-100 ha, respectively. These results provide the first precise and representative conventional sampling plan for scouting D. maidis adults grown in corn fields. Therefore, the conventional sampling plan for D. maidis determined in this study is practical and can be incorporated into integrated pest management programs for corn crops owing to its representativeness, precision, speed, and low cost.

Is insecticide resistance a factor contributing to the increasing problems with Dalbulus maidis (Hemiptera: Cicadellidae) in Brazil?

BACKGROUND: The corn leafhopper, Dalbulus maidis, is an important pest in Brazil. While chemical control has traditionally been the cornerstone for managing this pest, field control failures have been reported for some insecticides. To understand if these failures are due to resistance, we evaluated the susceptibility of 11 field-collected populations of D. maidis to major insecticides during the 2021-2022 crop seasons in Brazil using concentration-mortality bioassays. Additionally, we employed diagnostic concentration bioassays and foliar sprays at label-recommended rates in 8-10 populations collected during the 2022-2023 crop seasons. RESULTS: High susceptibility to methomyl, carbosulfan and acephate was observed on concentration-mortality bioassays across all populations tested with resistance ratio (RR) based on LC50 <10-fold, except for one population from Bahia State that exhibited reduced susceptibility to methomyl (RR = 17.5). On the other hand, all populations exhibited reduced susceptibility to bifenthrin, acetamiprid, and imidacloprid, with RR ranging from 90 to 2000-fold. This reduced susceptibility to neonicotinoid and pyrethroid insecticides was further confirmed at diagnostic concentrations based on LC99 of the susceptible strain, with survival rates >20% and in foliar sprays with mortality rates <80%. Most populations exposed to acephate and carbosulfan exhibited low survival rates at diagnostic concentrations (<5%) and high mortality rates in foliar sprays (>80%). CONCLUSIONS: The reduced susceptibility to pyrethroid and neonicotinoid insecticides likely explain the field failures in controlling D. maidis populations in Brazil. This study represents the first large-scale susceptibility monitoring of D. maidis to insecticides, and the results will contribute to decision-making regarding the management of this pest. © 2024 Society of Chemical Industry.

Distribution of Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae) and incidence of maize rayado fino virus and Candidatus Phytoplasma asteris in corn succession planting systems.

BACKGROUND: Corn is one of the main crops grown globally to produce food for human consumption and animal feed, including raw materials for bioenergy. Effective pest management is critical for the economic viability of corn production. The leafhopper Dalbulus maidis and the diseases transmitted by it have become relevant to corn production. Our study aimed to determine environmental parameters that affect D. maidis populations and the impacts of pathogen dispersion on corn productivity under different rotation systems and sowing seasons. RESULTS: The population density of leafhoppers found in the studied crops was low but capable of establishing the diseases and spreading them widely in the crops. The leafhopper's highest occurrence was in the corn vegetative development stage, and its population peaks were earlier in the corn off-season. The incidence of maize rayado fino virus and maize bushy stunt phytoplasma were higher in corn off-season than in the growing season. The incidence of diseases was higher in the final stages of the cultivation cycle. Yield losses were significantly higher for maize bushy stunt phytoplasma and not significant for maize rayado fino virus. CONCLUSION: Our study observed that corn's physiological stage was the main factor influencing D. maidis dynamics. The occurrence of D. maidis at low densities was sufficient to ensure the efficient transmission and dissemination of maize rayado fino virus and maize bushy stunt phytoplasma, which had a higher incidence in the reproductive stage and the corn sowed off-season. © 2023 Society of Chemical Industry.

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.

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.

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 90 days. 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 3 months 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.

Maize Bushy Stunt Phytoplasma Favors Its Spread by Changing Host Preference of the Insect Vector.

Plant pathogenic bacteria may influence vector behavior by inducing physiological changes in host plants, with implications for their spread. Here, we studied the effects of maize bushy stunt phytoplasma (MBSP) on the host selection behavior of the leafhopper vector, Dalbulus maidis (DeLong and Wolcott). Choice assays contrasting leaves of healthy (mock-inoculated) vs. infected maize (Zea mays L.) were conducted during the asymptomatic and symptomatic phases of plant infection, with leafhopper males or females previously exposed to infected plants (bacteriliferous insects) or not. In each assay, 40 adults were released in choice arenas where only the leaves of two plants from each treatment were offered and visible, and the insects landed on the leaves were counted 1, 2, 3, 5, 7, 9, 11 and 23 h after release. During the asymptomatic phase of plant infection, an effect was observed only on bacteriliferous females, who preferred leaves of healthy plants 5 h after release or later. The symptomatic phase triggered a pull-push effect on non-bacteriliferous females, who were first attracted to symptomatic leaves but hours later moved to healthy leaves. Non-bacteriliferous males initially preferred symptomatic leaves (up to 5 h after release) and later became equally distributed between treatments. Bacteriliferous males and females initially did not discriminate between healthy and symptomatic leaves, but only the females tended to move to healthy leaves 9 h after release. Oviposition was drastically reduced on symptomatic leaves. The changes in vector behavior induced by MBSP favor its primary spread, since bacteriliferous females prefer healthy leaves at early (asymptomatic) stages of the crop. At later stages, secondary spread may be favored because non-bacteriliferous females are initially attracted to infected (symptomatic) leaves, allowing pathogen acquisition and subsequent transmission as they move to healthy plants.

Control of Dalbulus maidis in maize crop with electrostatic spraying / Controle de Dalbulus maidis na cultura do milho com pulverização eletrostática

Among the pests that attack the maize, the maize leafhopper, which causes direct damages by sap-sucking and indirect ones, stands out as being a vector of pathogens and viruses, and can cause losses of up to 100% of the production. An alternative to improve the chemical control of this pest is the use of electrostatic spraying technology. However, there is no research support. This study aimed to evaluate the deposition of spray in the maize crop and the effectiveness in the chemical control of the maize leafhopper, using the electrostatic spraying system, at different application rates, compared to the conventional spraying system. The experiment was conducted in a randomized block design with five treatments, in a 2x2 + 2 factorial scheme: presence or absence of electrostatic spraying system, two application rates (35 and 50 L ha-1), an additional treatment using a hydraulic spray nozzle and a rate of 100 L ha-1, and other additional treatment without the application of insecticide, in order to support the study of pest infestation. Each treatment consisted of eight replicates, in which the spray deposition in the maize canopy and the efficiency in the control were evaluated. For the insecticide applications, a boom sprayer with induction electrostatic spraying system was used with indirect electrification. To evaluate the deposition, the Brilliant Blue FCF marker was added to the spray to be detected by absorbance in spectrophotometry. For the biological efficacy of the maize leafhopper, the insecticide composed of thiamethoxam and lambda-cyhalothrin was used compared with the control without the application. There was a significant increase in the spray deposition, both in the upper and lower maize leaves, with the use of electrostatic spray technology compared to the conventional spray system. The control of the maize leafhopper was also superior. The electrostatic spraying also made it possible to reduce the application rate by approximately three times in relation to that used in conventional hydraulic spraying.

Dentre as pragas que atacam a cultura do milho, atualmente destaca-se a cigarrinha do milho, causadora de danos diretos pela sucção de seiva e indiretos por ser um vetor de patógenos e vírus, podendo causar perdas de até 100% da produção. Uma alternativa para melhorar o controle químico desta praga é o uso da tecnologia de pulverização eletrostática, no entanto, ainda sem o devido respaldo da pesquisa. Esse trabalho objetivou avaliar a deposição de calda e a eficácia no controle da cigarrinha do milho, utilizando o sistema de pulverização eletrostática, comparado ao sistema convencional, em diferentes taxas de aplicação. O experimento foi conduzido no delineamento de blocos casualizados com cinco tratamentos, em esquema fatorial 2x2+2: presença ou ausência de sistema de pulverização eletrostático, duas taxas de aplicação (35 e 50 L ha-1), um tratamento adicional, empregando ponta de pulverização hidráulica e taxa de 100 L ha-1, e outro tratamento adicional sem aplicação de inseticida, com intuito de embasar o estudo de infestação da praga. Cada tratamento constou de oito repetições, nas quais foram avaliadas as deposições de calda e a eficácia no controle. Para as aplicações do inseticida, foi utilizado um pulverizador de barra com sistema de pulverização eletrostática por indução com eletrificação indireta. Para a avaliação da deposição, adicionou-se à calda o marcador Azul Brilhante para ser detectado por absorbância em espectrofotometria. Para a avaliação de eficácia biológica da cigarrinha do milho, foi utilizado o inseticida composto por tiametoxam e lambda-cialotrina, comparando com a testemunha sem aplicação. Houve um incremento significativo na deposição de calda, tanto nas folhas superiores quanto nas folhas inferiores do milho, com o uso da tecnologia de pulverização eletrostática comparada ao sistema de pulverização convencional. O controle fitossanitário da cigarrinha do milho também se mostrou superior. A pulverização eletrostática possibilitou ainda a redução da taxa de aplicação em aproximadamente três vezes em relação à utilizada na pulverização hidráulica convencional.

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

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.

Re-description of the sperm morphology of Dalbulus maidis (Hemiptera: Cicadellidae: Deltocephalinae).

The corn leafhopper, Dalbulus maidis, which is one of the most important vectors of maize diseases, had the morphology of its spermatozoa described more than 40 years ago. However, the description is imprecise, requiring certain rectifications. Hence, we re-describe the sperm morphology of this species using light microscopy and transmission electron microscopy. Their spermatozoa measured from 118.1 to 128.5 µm in length, this value being about three times smaller than what was previously described. The head region is formed by a small acrosome and the nucleus. The acrosome is paracrystalline and has the bifurcated base that is docked in two cavities on one side of the anterior region of the nucleus. The nucleus, which is linear and thin, measured from 19.3 to 22.9 µm in length, and exhibited homogeneously compact chromatin. In cross-section, it has a thumbtack shape, except in the anterior and posterior regions, where it is oval. The flagellum consists of an axoneme with 9 + 9 + 2 microtubules, two similar mitochondrial derivatives, two accessory bodies each associated with a small sub-ellipsoidal structure, and a 'center-flagellar material'. In all the spermatozoa observed, the final portion of the flagellum was branched into four filaments. Some of these morphological features are now being re-described, while others have been observed for the first time in the Cicadellidae family, as the center-flagellar material.

A Bird in the Hand Versus Two in the Bush? The Specialist Leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) Does Not Discriminate Against Sub-optimal Host Plants (Zea spp.).

The corn leafhopper [Dalbulus maidis (DeLong & Wolcott)] is a specialist on Zea (Poaceae) that coevolved with maize (Zea mays mays) and its teosinte (Zea spp.) relatives. This study tested the hypothesis that host acceptance by females varies among Zea hosts, and is correlated with variation in defensive levels across those hosts. Prior studies revealed differences in plant defenses among Zea hosts and corresponding differences in corn leafhopper performance. Thus, host acceptance was expected to be correlated with defensive levels and offspring performance across Zea hosts, following the hypothesis that offspring performance mediates host preference. In parallel, host acceptance was expected to be correlated with transitions in life history strategy (perennial to annual life cycle), domestication status (wild to domesticated), and breeding intensity (landrace to hybrid variety) in Zea because variation in defensive levels and corn leafhopper performance were shown in prior studies to be correlated with those transitions. The study's hypotheses were tested by comparing, under no-choice conditions, host acceptance by corn leafhopper of a suite of Zea hosts encompassing those transitions: perennial teosinte (Zea diploperennis), Balsas teosinte (Zea mays parviglumis), and landrace and commercial hybrid maize. The results did not show differences in host acceptance for oviposition or feeding among the hosts. Thus, under no-choice conditions, all Zea hosts may be similarly acceptable for feeding and oviposition, despite marked ovipositional preferences under choice conditions and poorer offspring performance on teosintes relative to maize shown previously. The results suggested also that oviposition frequency per plant by females was not correlated with their offspring's performance.

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.

Eficiência de inseticidas em tratamento de sementes de milho no controle da cigarrinha Dalbulus maidis (Hemiptera: Cicadellidae) em viveiro telado / Insecticides efficiency in treatment of corn seeds to control leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) in greenhouse

O objetivo deste trabalho foi verificar a eficiência de inseticidas no tratamento de sementes no controle da cigarrinha-do-milho em viveiro telado. Sementes de milho foram tratadas ou não com inseticidas (imidacloprid, thiamethoxan, thiodicarb + zn, thiodicarb, carbofuran, carbofuran + zn e carbosulfan) e semeadas em vasos plásticos. Nas plantas, foram confinadas cigarrinhas sadias e avaliada a eficiência desses inseticidas no controle desse inseto, em diferentes intervalos de tempo e em períodos sucessivos. Os produtos imidacloprid e thiamethoxan foram os mais eficientes no controle da cigarrinha, proporcionando eficiência de controle de adultos de D. maidis igual ou superior a 70 por cento, até o trigésimo dia de avaliação, após 4 a 24h de confinamento das cigarrinhas.

This research was aimed at checking the efficiency of insecticide seed treatment on corn leafhopper control, at greenhouse. Maize seeds were treated with insecticides (imidacloprid, thiamethoxan, thiodicarb + zn, thiodicarb, carbofuran, carbofuran + zn and carbosulfan) and sowed on plastic pots. On those plants healthy leafhoppers were confined, and the efficiency of those insecticides on its control was evaluated, at different intervals of time and in successive periods. The insecticides imidacloprid and thiamethoxan were the most efficient to control the corn leafhoppers, and provided control efficiency of D. maidis adults equal or upper 70 percent until the thirtieth day of evaluation, after 4 to 24h of leafhoppers confining.

Análise comparativa da estabilidade do DNA de Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) sob diferentes métodos de preservação para uso em RAPD-PCR / Comparative analysis of the stability of DNA of Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) under different methods of preservation for use in RAPD-PCR

The appropriate preservation of the DNA of a certain organism is important for successful application of molecular techniques like RAPD-PCR. This study was designed to compare simple methods of preservation of specimens of Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) with respect to quantity and quality of DNA for use in RAPD-PCR, after different storage periods. Eight methods were tested: freezing (-20°C); ethyl alcohol 70 percent (-20°C and room temperature); absolute ethyl alcohol (-20°C and room temperature); air-dry; and preservation in extraction buffer (whole and homogenized insect). At intervals of 10 to 30 days, insect DNA was extracted, quantified and amplified through RAPD-PCR using primer OPA-04. The quality of extracted DNA was observed on 0.8 percent agarose gel. After 210 days of preservation, freezing (-20°C) showed to be the best method. Satisfactory quantities of DNA were also obtained from insects conserved in absolute ethyl alcohol (-20°C), ethyl alcohol 70 percent (-20°C) and extraction buffer (whole and homogenized insect). Insects conserved in absolute ethyl alcohol (room temperature), ethyl alcohol 70 percent (room temperature) and air-dry conditions were inappropriate for RAPD-PCR studies after 120, 60 and 10 days of storage, respectively.

A preservação adequada do DNA de um determinado organismo é fundamental para o sucesso no uso de técnicas moleculares como RAPD-PCR. O objetivo deste trabalho foi comparar métodos simples de preservação de espécimes de Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) quanto à quantidade e qualidade do DNA para uso em RAPD-PCR, após períodos sucessivos de armazenamento. Avaliaram-se oito métodos: congelamento (-20°C); álcool etílico 70 por cento (-20°C e temperatura ambiente); álcool etílico absoluto (-20°C e temperatura ambiente); secagem ao ar; e preservação em tampão de extração (inseto inteiro e macerado). A intervalos de 10-30 dias, o DNA foi extraído, quantificado e amplificado via RAPD-PCR pelo oligonucleotídeo OPA-04. A qualidade do DNA extraído foi observada em gel de agarose 0,8 por cento. Após 210 dias de armazenamento, o congelamento (-20°C) mostrou ser a melhor técnica. Quantidades satisfatórias de DNA também foram obtidas dos insetos conservados em álcool etílico absoluto (-20°C), álcool etílico 70 por cento (-20°C) e tampão de extração (inseto inteiro e macerado). Insetos conservados em álcool etílico absoluto (temperatura ambiente), em álcool etílico 70 por cento (temperatura ambiente) e secos ao ar mostraram-se impróprios para estudos com RAPD-PCR após 120, 60 e 10 dias de armazenamento, respectivamente.