Corn Leafhopper Research Articles

The First Standardised Sampling Plan Designed to Scout Dalbulus maidis (Hemiptera: Cicadellidae) Adults in Corn Crops Using Yellow Sticky Traps

ABSTRACTThe corn leafhopper Dalbulus maidis (Hemiptera: Cicadellidae) is one of the main pests in corn crops causing yield reductions of up to 70%. Dalbulus maidis primarily damages corn by transmitting pathogens. Direct plant damage is caused by sap suction and toxin injection. Sampling corn fields to determine the D. maidis density for decision‐making systems can be challenging due to field size, time and cost. Yellow sticky traps (YST) are commonly employed to determine the presence and density of D. maidis because they are easy to use and allow quick and low‐cost assessment. This study aimed to propose and evaluate a new sampling plan for D. maidis in corn crops using YST. This research was carried out in commercial corn crops in the Brazilian Atlantic Forest and Cerrado biomes for 3 years. The pest density in traps and on plants were moderately (r = 0.54–0.66) and significantly (p < 0.0001) correlated. The density evaluated in the traps showed relative variance of less than 25% and sampling time of up to 2 min per sample unit. The negative binomial distribution was adequate to represent the D. maidis density probability distribution for the YST sampling method with K common (2.8979) among all the fields evaluated. The sampling plan consisted of installing one trap every two hectares. The plan's total cost ranged from US$/ha 0.41 to 0.50, with a total sampling time of up to 2.5 min/ha. We propose this new sampling plan for D. maidis, which is suitable for incorporation into management programmes in corn crops, as it is representative, accurate, fast and low cost.

Insights into the RNA Virome of the Corn Leafhopper Dalbulus maidis, a Major Emergent Threat of Maize in Latin America

The maize leafhopper (Dalbulus maidis) is a significant threat to maize crops in tropical and subtropical regions, causing extensive economic losses. While its ecological interactions and control strategies are well studied, its associated viral diversity remains largely unexplored. Here, we employ high-throughput sequencing data mining to comprehensively characterize the D. maidis RNA virome, revealing novel and diverse RNA viruses. We characterized six new viral members belonging to distinct families, with evolutionary cues of beny-like viruses (Benyviridae), bunya-like viruses (Bunyaviridae) iflaviruses (Iflaviridae), orthomyxo-like viruses (Orthomyxoviridae), and rhabdoviruses (Rhabdoviridae). Phylogenetic analysis of the iflaviruses places them within the genus Iflavirus in affinity with other leafhopper-associated iflaviruses. The five-segmented and highly divergent orthomyxo-like virus showed a relationship with other insect associated orthomyxo-like viruses. The rhabdo virus is related to a leafhopper-associated rhabdo-like virus. Furthermore, the beny-like virus belonged to a cluster of insect-associated beny-like viruses, while the bi-segmented bunya-like virus was related with other bi-segmented insect-associated bunya-like viruses. These results highlight the existence of a complex virome linked to D. maidis and paves the way for future studies investigating the ecological roles, evolutionary dynamics, and potential biocontrol applications of these viruses on the D. maidis—maize pathosystem.

First Report of Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae) in Oklahoma.

The corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae), is an invasive insect that can cause damage to maize (Zea mays L.) in two ways: by direct feeding and the transmission of several plant pathogens. Dalbulus maidis is an invasive and serious economic pest of maize that has spread from its center of origin in Mexico to the southernmost parts of the United States. Prior to 2024, corn leafhoppers had not been documented in Oklahoma, and their spread northward toward the United States corn belt is of significant concern. Here, we provide the first reports of the insect in maize in several Oklahoma counties. Insect specimens were collected at various commercial and experimental field sites by Oklahoma State University research and extension personnel. The identity of the insect species was validated through morphological and molecular taxonomy. The presence records for the corn leafhopper presented here provide valuable information for future monitoring and management efforts of this economically important pest and disease.

Comprehensive analysis of biochemical compounds, chemical elements and metabolites modifications in maize plants infected with maize rayado fino virus (MRFV)

Maize cultivation is crucial worldwide, especially in Latin America. However, diseases related to corn stunt complex have significantly impacted crops, reducing grain productivity and quality. Maize rayado fino virus (MRFV) is part of this complex, and its symptom is characterized by chlorotic dots along veins and, depending on maize genotype, there will be stunting and an impact on the corn cob development, which can lead to productivity losses. However, this intricate plant-pathogen relationship is yet not well understood. Here, we investigated the effects of MRFV transmitted by the corn leafhopper Dalbulus maidis in infected plants in their early stage of development. To show the impact of the viral infection in the maize plant, we performed biochemical and chemical analysis and nuclear magnetic resonance (NMR). The total set of analyses showed that changes in chemical and biochemical compounds, as well as in metabolites composition and activities, can be perceived in MRFV-infected maize plants when compared to healthy plants. An increase in the activity of superoxide dismutase, catalase, peroxidase, and β-glucanase was detected, whereas small changes have been identified in antioxidant activity and phenolic compounds. For chemical components, unique changes were observed, mainly the increase in the presence of some elements such as calcium (Ca), phosphorus (P), sodium (Na), and iron (Fe). We identified 20 metabolites of the amino acids, organic compounds, and carbohydrates classes in maize plants which are regulated during MRFV infection. Maize plants reacted to D. maidis herbivory by modulating both enzymatic and non-enzymatic activities, as well as chemical compounds. This research offers insights into the responses of maize against MRFV and sheds light on parameters to be used on the search of rayado fino viral disease resistance for a sustainable production.

Susceptibility of corn hybrids to corn stunt complex transmitted by the corn leafhopper, Dalbulus maidis (DeLong & Wolcott, 1923) in Brazil

Corn (Zea mays L.) production plays a key role in the global agricultural scenario. Corn is currently the most produced cereal in the world, with more than 1.1 billion tons harvested in 2021. The main pest that affects corn in Latin America is the corn leafhopper (Dalbulus maidis) (DeLong & Wolcott, 1923). This insect causes direct damage to Zea mays plants through suction of the corn sap, but its importance is greater due to the transmission of two phytopathogens of the mollicute class: the phytoplasma (MBSP – maize bushy stunt phytoplasma) that causes the red stunting; and spiroplasma (Spiroplasma kunkelii) which causes pale stunting; in addition to a virus, the corn stripe virus (MRFV – maize rayado fino virus). Stunting is a systemic disease that affects the physiology, nutrition, and development of the corn crop, significantly reducing its productivity. Therefore, the use of resistant hybrids is the main alternative to reduce the incidence and damage caused by corn stunting. This work aimed to evaluate the susceptibility of maize hybrids to the stunting complex transmitted by the corn leafhopper in three different sowing dates. The experiment was carried out with 63 corn hybrids in three different sowing times, the first being on 11/24/2022, the second on 12/30/2022 and the third on 02/06/2023. The hybrids SHSuper CONV, NTX454 VT PRO2 and FS670 PWU were the ones that had the lowest rates of stunting severity, showing a high resistance to this disease complex. The hybrids AG9025 PRO3, DKB240 PRO3 and K9300 PRO3 were the ones that presented the highest disease severity scores (6 to 5.7 on the scale used), indicating a high susceptibility to the stunt pathogens complex. The use of less susceptible hybrids is one of the main components for managing stunting diseases complex in the corn crop in South America, being one of the most important features, together with potential yield, as a parameter for growers to select the hybrid to be used.

Temporal resource continuity for egg parasitoids of Dalbulus maidis (Hemiptera: Cicadellidae) during winter on irrigated maize crops and edge grasses.

Little is known about winter-season parasitism of eggs of the corn leafhopper Dalbulus maidis DeLong (Hemiptera: Cicadellidae), an important pest of maize throughout the Americas. Our study, conducted in Mexico, aimed to characterize winter-season parasitism of corn leafhopper eggs on maize crops cultivated with drip irrigation and on wild grasses that grow on the edges of maize crops when maize is not present. Maize leaves baited with D. maidis eggs were used to trap the egg parasitoids in the field. In the first year (2022), parasitism of D. maidis eggs was investigated in maize fields planted contiguously on different dates (asynchronous planting). In the second year (2023), parasitism of D. maidis eggs was evaluated in edge grasses and in adjacent maize crops planted on the same date (synchronous). The highest percentage of parasitism (53%), percentage of emergence, and total abundance of egg parasitoids were found in asynchronous maize fields. Here, Anagrus virlai Triapitsyn (Hymenoptera: Mymaridae), Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae), and Pseudoligosita sp. (Hymenoptera: Trichogrammatidae) wasps were found parasitizing the D. maidis eggs, with P. subflava being the most abundant. In wild edge grasses, only P. subflava was found, showing low levels of parasitism, while in synchronous maize, P. subflava increased its percentage of parasitism (up to 37%), percentage of emergence, and abundance, during winter. These results suggest that P. subflava acts as an efficient biological control agent of D. maidis in irrigation-grown maize crops during the winter season, and that edge grasses are overwinter habitats for P. subflava.

Effect of microfilaments produced by eggs of Dalbulus maidis (Hemiptera: Cicadellidae), against egg parasitoids

Abstract Insect eggs, once oviposited, defend against abiotic and biotic factors using thickness, secretions, or other defenses. The eggs of most insect species are attacked by parasitoid wasps, which are often their most significant mortality factors. The present study is the first investigation of microfilaments as defense from parasitoids. Specifically, the effect of the corn leafhopper Dalbulus maidis DeLong (Hemiptera: Cicadellidae) egg microfilaments against parasitism by Anagrus virlai Triapitsyn (Hymenoptera: Mymaridae) and Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae) was evaluated. Field and laboratory experiments were conducted to evaluate several biological traits related to parasitism in D. maidis eggs with and without microfilaments. An initial field experiment found no difference in parasitism by A. virlai and P. subflava of eggs with vs. without microfilaments after 5 days of exposure of healthy D. maidis eggs to parasitism. A second field experiment then looked at exposure for 1 day, and this treatment found greater parasitism of healthy D. maidis eggs by each parasitoid species in eggs without microfilaments vs. in eggs with microfilaments. Laboratory experiments conducted separately for A. virlai and P. subflava parasitism after 1 day of exposure to healthy D. maidis eggs confirmed a higher percentage of parasitoid emergence in the eggs without microfilaments (both young and mature eggs) vs. mature eggs with microfilaments. These results suggest that eggs without microfilaments are more parasitized than eggs with microfilaments during a 1-day exposure, but that this difference disappears as egg microfilaments regrow over a 5-day period.

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

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. 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%). 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.

Plant‐mediated facilitation to conspecifics and heterospecifics by two phloem‐feeding maize pests: The influence of insect identity and order of arrival

Abstract Herbivory by insects leads to changes in both primary and secondary plant metabolism, ultimately impacting subsequent interactions. Some phloem‐feeding insects have developed mechanisms to suppress herbivore‐induced plant defences and manipulate the quality of host phloem sap, thereby facilitating their establishment on the host plant. Based on evidence that the specialized phloem‐feeding insects, Dalbulus maidis and Rhopalosiphum maidis, can suppress herbivore‐induced defences in maize, we hypothesized that infestation by either of these pests in maize would facilitate the colonization and establishment of subsequent conspecific and heterospecific individuals. We conducted a series of behavioural assays with these insects in both laboratory and greenhouse settings. The corn leafhopper D. maidis preferred previously infested plants as hosts, but it did not discriminate between conspecific‐ or heterospecific‐infested plants for colonization. However, when selecting a host for oviposition, it preferred depositing eggs on conspecific‐infested plants, which were the hosts that the offspring performed better compared to both non‐infested and heterospecific‐infested plants. The corn aphid R. maidis also preferred previously infested plants over non‐infested plants as hosts. However, the aphid preferred heterospecific‐infested over conspecific‐infested plants, even though heterospecific‐infested plants were hosts of lower quality to aphids. Aphids performed better on conspecific‐infested plants, followed by heterospecific‐infested plants, when compared to non‐infested plants. Our results confirm that previous colonization by the specialized phloem‐feeding insects facilitates subsequent infestations by conspecifics and heterospecifics. However, the facilitation for heterospecifics was asymmetric, as colonization by D. maidis facilitated infestations by R. maidis more than the reverse sequence of infestation.

Effects of food resources on the longevity, survival, and fecundity of Paracentrobia subflava adults, an egg parasitoid of the corn leafhopper pest Dalbulus maidis

AbstractThe diet consumed by adult parasitoids can affect longevity, survival, and fecundity. Honeydew from sap‐sucking insects is an abundant food resource in the field; however, artificial diets such as commercial bee honey are often used in lab rearing. The parasitoid Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae) is a natural enemy of Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae). The longevity and survival of P. subflava when fed natural and artificial diets under controlled conditions have not been studied. Further, the fecundity of P. subflava when fed a diet of honey has not been investigated. Therefore, our first objective was to analyse the longevity and survival of P. subflava when fed (1) honeydew of the corn leafhopper D. maidis, (2) honey + water, (3) honey + water + pollen, (4) water, and (5) nothing (control). Our second objective was to evaluate P. subflava fecundity upon exposure to D. maidis eggs, comparing parasitoids fed with honey + water versus controls (no food or water). In the second objective, honey was chosen since it was determined during the first objective to be the optimal food. The longevity of adult parasitoids (laboratory‐reared and field‐collected) was high when fed on honey and low when fed other diets. The highest longevity was achieved with honey + water: 17 days, while the survival of adult parasitoids was only 3 days for honeydew. Interestingly, fecundity, in terms of the percentage of parasitism and the percentage of emergence, did not differ between parasitoid females that had access to honey + water as a food resource and those that had no food or water.

Prevalence of insect pests on maize crop in District Mansehra, Khyber Pakhtunkhwa, Pakistan.

The maize crop is used as food for humans, livestock and poultries forms, it is also used in bread making, corn flakes, corn syrup, corn starch and corn oils. The field study consisted of one experimental trial, about the incidence of that insect pest complex on maize cultivar Azam during the Kharif season 2020 at the Agricultural, Research Station, Baffa, Mansehra. The trial was laid out in the Randomized Complete Block Design (RCBD), and then it was divided into three replications. The result obtained from the trial showed that a number of the pest species were recorded during the experimental period; however, the population was noticed at a low level. The obtained insect species were corn leaf aphid (6.90 ± 5.5) per square inch, corn leafhopper (1.32 ± 0.63), maize stem borer (0.63 ± 0.29), corn flea beetle (0.43 ± 0.28), Thrips (0.38 ± 0.22), Hairy caterpillar (0.21 ± 0.22), Grasshopper (0.17 ± 0.11) and shoot fly (0.11 ± 0.08) throughout the season.

Biorational control of corn leafhopper and activation of resistance with compounds from Morinda citrifolia.

Currently, the increasing productivity, garanee phytosanitary measures, and food security in plantations is a significant challenge. The potential of plant compounds in pests and diseases alternative control has been widely researched. This study is the first to investigate the use of the plant Morinda citrifolia L.(noni) for managing maize leafhoppers, a major issue in plantations. The effects of essential oil and octanoic acid on resistance induction were evaluated with quantification of phytoalexins, potential phytotoxicity, and toxicity to corn leafhopper, Dalbulus maidis. The chromatographic analysis identified octanoic acid as the primary compound, constituting 58.43% of the essential oil. The elicitor potential was more pronounced in plants treated with M. citrifolia compounds than in those treated with commercial resistance-activating products. The essential oil effectively controlled D. maidis, resulting in 50% mortality after 48 hours without damaging the leaf area. These findings highlight the potential of M. citrifolia in the biorational control of the stunting complex, with effective vector control and resistance induction.

DC-electrical penetration graph waveforms for Dalbulus maidis (Hemiptera: Cicadellidae) and the effects of entomopathogenic fungi on its probing behavior

The corn leafhopper Dalbulus maidis is an important transmitter of viruses and bacteria to maize plants. Data on the stylet probing and ingestion behavior of D. maidis, gathered using the DC-electrical penetration graph (DC-EPG) technique, are limited. The increasing prevalence of this pest and the diseases that it transmits in maize crops heighten the importance of studying how control tools affect the probing behavior of these insects, to reduce or prevent the chances of pathogen transmission and the damage from feeding. Our study recorded stylet activities of D. maidis, using a DC-EPG system and compared the appearances of waveforms with those from published AC and AC-DC EPG studies. All types of systems produced similar waveform appearances; therefore, we used the waveform nomenclature previously published. We also determined the effects of the entomopathogenic fungus Cordyceps javanica on the probing behavior of D. maidis at different time points after the fungus was applied by spraying. Forty-eight hours after the insects were sprayed, the effects were pronounced, with significant disruption of the stylet activities in phloem and non-phloem phases. Our study indicated that this commercial microbiological product, with the active ingredient C. javanica, can alter the probing behavior of D. maidis and may be helpful in management of the vector.

Does the corn leafhopper Dalbulus maidis (DeLong &amp; Wolcott) (Hemiptera: Cicadellidae) reproduce in hosts other than maize?

The corn leafhopper Dalbulus maidis (DeLong &amp; Wolcott) (Hemiptera: Cicadellidae) is a specialist insect vector of the corn stunting disease complex. This leafhopper has been reported from different overwintering plants, and more information is required regarding other potential Brazilian plants that may serve as reproductive hosts for this specie. The present study aimed to evaluate possible plants for leafhopper reproduction usually found near the maize fields and the D. maidis reproductive differences among maize genotypes. Three trials were conducted to assess D. maidis survival and oviposition on different maize genotypes and other potential host plants. Survival, nymph presence, oviposition, and nymph eclosion rates were observed. No nymphs were observed in plants other than maize. The number of D. maidis adults was influenced by the different maize inbreds, and the mean number of laid eggs varied across the tested maize materials. Oviposition and nymph emergence was observed in pearl millet [Pennisetum glaucum (L.) R. Br., Poaceae] when D. maidis adults were offered only this plant as substrate, although significantly lower than those recorded on maize. Our results suggest that eliminating maize plants in the off-season could be used as a tool to reduce D. maidis reproduction, thereby minimizing the vector population size in the following season.

Insecticides for corn leafhopper management versus entomopathogenic fungal isolates: In vitro compatibility, physical-chemical interactions, and on-farm assessments

This study is the first investigation of the biological compatibility of isolates IBCB 66 and Simbi BB15 of Beauveria bassiana and Esalq-1296 of Cordyceps fumosorosea, registered in Brazil for the management of corn leafhopper Dalbulus maidis, with synthetic insecticides used in the management of sucking insects in the initial growth stage of maize crops. The biological index was used to identify the most compatible synthetic insecticides with each fungal isolate tested and isolate IBCB 66 of B. bassiana was the most sensitive. In addition, most mixtures of synthetic insecticides with mycoinsecticides were physically compatible, except for the mixture of mycoinsecticide based on isolate Simbi BB15 of B. bassiana (OD formulation) with insecticides based on acephate, profenophos + cypermethrin, and dinotefuran + lambda-cyhalothrin, which showed absence of homogeneity. Field trials (on-farm assessments) of two-crop seasons indicate that compatibility of insecticides with mycoinsecticides is a key factor for the effectiveness of mixtures in D. maidis population suppression, reduction of incidence and severity of corn stunt complex (CSC), and yield of corn crops. The mixtures of imidacloprid + beta-cyfluthrin and imidacloprid + bifenthrin with mycoinsecticides based on B. bassiana (isolate Simbi BB15) and C. fumosorosea (isolate Esalq-1296) showed the best results in all parameters assessed. Thus, the association of mycoinsecticides with synthetic insecticides is a promising alternative for the management of the corn leafhopper and CSC pathosystem. However, the compatibility of synthetic insecticides is crucial for the success of the associated use of chemical and fungal agents.

On-farm Production of Microbial Entomopathogens for use in Agriculture: Brazil as a Case Study.

In Brazil, the production of beneficial microorganisms by growers exclusively for their own use is a practice known as "on-farm production". Regarding on-farm bioinsecticides, they were initially deployed for pests of perennial and semi-perennial crops in the 1970s but, since 2013, their use has extended to pests of annual crops such as maize, cotton, and soybean. Millions of hectares are currently being treated with these on-farm preparations. Local production reduces costs, meets local needs, and reduces inputs of environmentally damaging chemical pesticides, facilitating establishment of more sustainable agroecosystems. Critics argue that without implementation of stringent quality control measures there is the risk that the on-farm preparations: (1) are contaminated with microbes which may include human pathogens or (2) contain very little active ingredient, impacting on field efficacy. The on-farm fermentation of bacterial insecticides predominates, especially that of Bacillus thuringiensis targeting lepidopteran pests. However, there has been a rapid growth in the past 5years in the production of entomopathogenic fungi, mostly for the control of sap-sucking insects such as whitefly (Bemisia tabaci (Gennadius)) and the corn leafhopper (Dalbulus maidis (DeLong and Wolcott)). In contrast, on-farm production of insect viruses has seen limited growth. Most of the ca. 5 million rural producers in Brazil own small or medium size properties and, although the vast majority still do not practice on-farm production of biopesticides, the topic has aroused interest among them. Many growers who adopt this practice usually use non-sterile containers as fermenters, resulting in poor-quality preparations, and cases of failure have been reported. On the other hand, some informal reports suggest on-farm preparations may be efficacious even when contaminated, what could be explained, at least partially, by the insecticidal secondary metabolites secreted by the pool of microorganisms in the liquid culture media. Indeed, there is insufficient information on efficacy and mode of action of these microbial biopesticides. It is usually the large farms, some with > 20,000ha of continuouscultivated lands, that produce biopesticides with low levels of contamination, as many of them possess advanced production facilities and have access to specialized knowledge and trained staff. Uptake of on-farm biopesticides is expected to continue but the rate of adoption will depend on factors such as the selection of safe, virulent microbial strains and implementation of sound quality control measures (compliance with emerging Brazilian regulations and international standards). The challenges and opportunities of on-farm bioinsecticidesare presented and discussed.

First report of maize rayado fino virus in corn fields in Santa Catarina, Brazil.

Maize (Zea mays L.) is the main cereal food of humans and animals in Brazil. In 2020 and 2021, a severe infestation of corn leafhoppers (Dalbulus maidis; Hemiptera: Cicadellidae) was observed in Santa Catarina State (South of Brazil). Subsequently, symptoms of chlorotic stripes limited in leaf veins started to appear in maize plants. Given the similarity of symptoms and the presence of high populations of corn leafhoppers in corn production areas, 30 plants in reproductive stage showing systemic symptoms were collected in summer and autumn from commercial fields of five municipalities in Santa Catarina: Campos Novos (27°23'18.0"S, 51°12'52.7"W), Lages (27°47'17.8"S, 50°18'16.9"W), Mafra (26°06'42"S, 49°48'25"W), Fraiburgo (27°01'36"S, 50°55'19"W), and Abelardo Luz (26°34'02"S, 52°20'02"W). The young leaves of these samples were used for molecular analyses targeting the maize rayado fino virus (MRFV; Tymoviridae: Marafivirus). Total nucleic acids were extracted using TRIzol® (Invitrogen, USA), following the manufacturer's instructions. These were used as a template for cDNA synthesis with the enzyme MMLV-RT (Promega, USA), following the manufacturer's instructions. The polymerase chain reaction (PCR) was performed using Gotaq® DNA polymerase (Promega, USA) and MRFV-09/MRFV-10 primers (Hammond et al. 1997). All PCR products were subjected to electrophoresis in 1% agarose gel and were visualized under ultraviolet light. Twenty-eight of the 30 tested plants were MRFV-positive, showing a fragment with an expected size of ~633 bp. To confirm our results, all MRFV-positive samples were sent for sequencing (GenBank accession numbers OM763708 - OM763710 and ON730784 - ON730806) and submitted to BLASTn search (https://blast.ncbi.nlm.nih.gov/Blast.cgi), resulting in identities ranging from 96.21% to 99.21% with the isolate "Brazil 26" of MRFV, which was detected in 2005 in São Paulo, Brazil (GenBank accession nº: AF186178) (Hammond and Bedendo 2005). A second set of primers was used to validate the first PCR, confirming MRFV infection (data not shown).Moreover, whitish streaks and leaf reddening were observed on the leaves of some plants; therefore, the identification for phytoplasmas (Candidatus Phytoplasma asteris) and spiroplasmas (Spiroplasma kunkelii) from the corn stunt complex was performed. For this, previously extracted nucleic acids from each sample were used as templates for a multiplex PCR using the primers CSSR6/CSSF2 and R16F2n/R16R2 (Gundersen and Lee 1996; Barros et al. 2001). Two plants were infected with only spiroplasma, 17 samples were infected with Spiroplasma and MRFV, and three samples were infected by these three pathogens. An increasing incidence of corn stunt has been observed in commercial fields in Santa Catarina in recent years. Mollicutes are commonly found and mostly studied as causal agents of corn stunt disease. On the contrary, despite being present in Brazil since the 1970s, the virus is less studied because its contribution to the corn stunt complex is still unknown (Hammond and Bedendo 2001). In this report, indications that the virus is expanding to different regions in southern Brazil were observed, which raises an opportunity for further evaluation and its consideration in monitoring programs. Moreover, to the best of our knowledge, this is the first report of MRFV in Santa Catarina, Brazil.

Implications of combined taxonomic, morphometric, and molecular characteristics for the species status of Paracentrobia tapajosae and Paracentrobia subflava (Hymenoptera: Trichogrammatidae), egg parasitoids of different leafhopper hosts in the Americas

The present study evaluated the taxonomy, morphology, and molecular variation of the egg parasitoids Paracentrobia subflava developing within eggs of the corn leafhopper Dalbulus maidis from Mexico, and Paracentrobia tapajosae developing within eggs of Tapajosa rubromarginata and eggs of D. maidis from Argentina. The parasitoids from the different host species were found to have a significant difference in body size and morphology of head, wings, ovipositor, and chaetotaxy. On the other hand, geometric morphometric analysis of the male genitalia showed no difference between parasitoids emerged from T. rubromarginata and D. maidis. Additionally, the COI and ITS2 molecular markers demonstrated that the parasitoids emerging from these two different hosts cluster into a single clade. This new information suggests the placement of P. tapajosae syn. nov. as a junior synonym of P. subflava.

Probing behavior of the corn leafhopper Dalbulus maidis on susceptible and resistant maize hybrids.

The corn leafhopper Dalbulus maidis is the main vector of the pathogens that cause corn stunt, a major disease of maize in the Americas. In line with plant resistance being an efficient tool to control diseases, the findings of a previous work showed that some corn hybrids are resistant to D. maidis. In this work, we assessed the probing behavior of D. maidis on susceptible and resistant corn hybrids using EPG (Electrical Penetration Graph) technology. Feeding of fifteen-day-old, non-inoculative females was recorded for 20 hours, with access to hybrids DK390, DK670, DK79-10, and DK72-10. Compared to the susceptible hybrid DK670, the other hybrids shifted D. maidis probing behavior in a way consistent with plant resistance to insects. This shift consisted of a higher number of probes of short duration, difficulties in attaining phloem ingestion and increase in xylem ingestion. In addition to this common shift in probing behavior, a phloem-located resistance factor was inferred in DK72-10 based on the longer time spent in phloem conditioning to attain phloem ingestion. In contrast, DK390 expressed the highest level of mesophyll and phloem-based resistance, in both cases seen with repeated attempts of short duration, a behavior typically associated with failed attempts to ingest. These findings support and are consistent with previous research, providing useful information to characterize maize hybrids resistant to D. maidis, and consequently to corn stunt.

Development of efficient RNAi methods in the corn leafhopper Dalbulus maidis, a promising application for pest control.

The corn leafhopper Dalbulus maidis is the main vector of important stunting pathogens that affect maize production. Currently, there are no effective methods available to manage this pest without adverse impact on the environment. In this context, genomic-based technologies such as RNA interference (RNAi) provide a more environmentally friendly pest control strategy. Therefore, we aimed to assess the application of RNAi in D. maidis and determine the function of a candidate gene related to insect reproduction and propagation. We have characterized the core RNAi genes and evaluated the functionality of the RNAi machinery. We assessed the potential of RNAi technology in D. maidis via injection or ingestion of double-stranded RNA (dsRNA) to adult females. We chose Bicaudal C (BicC) as a target gene due to its important role during insect oogenesis. Administration of dsRNABicC caused significant reductions in the transcript levels (fold changes up to 170 times) and ovipositions. Phenotypic analysis of the ovaries revealed alterations in oocyte development, providing additional confirmation for our results and supporting the idea that Dmai-BicC is a key player of D. maidis oogenesis. This is, to our knowledge, the first report of efficient RNAi in D. maidis. We believe our findings provide a starting point for future control strategies against one of the most important maize pests in the Americas. © 2022 Society of Chemical Industry.