Response of maize hybrids to corn stuntdisease caused by <i>Spiroplasma kunkelii </i>in the Argentine Northwest (NOA) – 2023-2024 growing season

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.

Corn production in several areas of Brazil recently has been seriously afflicted by a disease commonly referred to as "red stunt," characterized by stunting and leaf reddening. Early observations that a phytoplasma was associated with the disease were confirmed through molecular analysis, which revealed the presence of maize bushy stunt phytoplasma (MBS) (1). Another disease of corn, corn stunt, is considered to be caused by one or more of a complex of MBS, corn stunt spiroplasma (CSS), and Maize rayado fino virus (MRFV), which can all be transmitted simultaneously by their leafhopper vector Dalbulus maidis (Delong & Wolcott). The contributions of CSS and MRFV to the recently described "red stunt" disease in Brazil are unknown. A virus serologically related to MRFV, Brazilian corn streak virus, was first identified in Sao Paulo State, Brazil, in the early 1970s; serological studies indicated that isolates of Brazilian corn streak virus were related to, but distinguishable from, MRFV isolates from other Latin American countries (4). Therefore, there was a high probability that MRFV would be found in maize tissues collected from plants exhibiting symptoms of "red stunt" disease. Maize leaf samples exhibiting symptoms of "red stunt" disease were collected and preserved by drying from four Brazilian States during 1995 and 1996 (1). Total nucleic acid extracts were prepared from dried leaf tissue and aliquots of the extracts were spotted onto a nylon membrane, which subsequently was hybridized to an MRFV-specific cRNA probe (3). Of the 37 samples tested for the presence of MRFV by nucleic acid hybridization, 16 were positive for MRFV. It was present in some, but not all, samples that were positive for MBS (1). MBS was detected in six, and CSS was detected by polymerase chain reaction (PCR) (2) in 12 samples. In 8 of the 37 samples, both CSS and MRFV were present, 4 of 37 were positive for MBS and MRFV, and in 3 of 37 samples, all three pathogens were detected. Therefore, there is not a clear correlation between the presence of MRFV and the symptoms of "red stunt." The coat protein gene and adjacent 3' nontranslated region of MRFV were amplified from infected tissues by reverse transcription-polymerase chain reaction (RT-PCR) using MRFV-specific primers (3). Three cloned PCR products were sequenced (deposited at GenBank under accession nos. AF186177 to AF186179), which revealed that the nucleotide sequences of the Brazilian isolates were 98% sequence identical and shared 90 to 97% identity with other MRFV isolates (3). Phylogenetic analysis of the sequences revealed close relationships to MRFV isolates from Peru and Bolivia, which neighbor Brazil (3). The contribution of MRFV to the stunting and leaf reddening symptoms exhibited by maize plants with "red stunt" disease is unknown. Of the 37 samples examined in this study, MRFV was detected in 16. A more complete epidemiological study of the association of MBS, CSS, MRFV, and their insect vector with "red stunt" disease will provide information on the significance of these pathogens in the current disease outbreak.

A incidência de doenças causadas por molicutes e por vírus foi avaliada em lavouras de milho (Zea mays) nas Províncias de Tucumán e de Córdoba, na Argentina, em fevereiro de 2000. Na Província de Tucumán verificou-se que 44% das lavouras apresentaram altos níveis de incidência de plantas com sintomas de enfezamentos causados por molicutes (50 a 100%), em altitudes variando de 300 a 2.000 m. A presença de fitoplasma e de espiroplasma foi confirmada em amostras de folhas de plantas com sintomas de enfezamentos, através dos testes de PCR e de "Western blotting". Constatou-se, porém, que a eficiência desses testes para detecção destes patógenos, quando os sintomas apresentados pelas plantas eram muito acentuados, foi da ordem de 70%, e de apenas 30% quando os sintomas eram menos acentuados. Na localidade Jesus Maria, foram encontradas plantas apresentando acentuado nanismo, folhas estreitas e com deformações. Dentre quatro amostras destas plantas, submetidas a testes de PCR, em duas foi detectada a presença de fitoplasma, possivelmente d istinto do "Maize Bushy Stunt Phytoplasma". A cigarrinha Dalbulus maidis, inseto vetor dos molicutes, foi encontrada apenas em Tucumán, estando ausente em Córdoba. O Mal de Rio Cuarto virus foi detectado em seis lavouras em Córdoba, e em três em Tucumán. A cigarrinha Delphacodes kuscheli foi detectada em todas as lavouras em Córdoba, e em apenas três lavouras em Tucumán. O Maize dwarf mosaic virus foi detectado em cerca de 60% das lavouras amostradas nas duas Províncias e o Maize rayado fino virus em apenas uma localidade em Tucumán.

Corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae), is native to Central and South America, but invasive in the United States. This species is a threat to corn, Zea mays L., one of the main crops of economic importance in the US, because it is also a vector of three pathogens responsible for corn stunt diseases complex: corn stunt spiroplasma (CSS), maize bushy stunt phytoplasma (MBSP), and maize rayado fino virus (MRFV). Therefore, monitoring the dispersal of this pest is necessary to document its geographic expansion and anticipate the incidence of corn stunt disease. Based on trap catches obtained from the Midwest Suction Trap Network in 2024, corn leafhopper populations increased late in the growing season in Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, and Wisconsin. We will continue to monitor the dispersal of this invasive species through the Midwest Suction Trap Network to provide information to researchers, extension agents, and producers regarding this agronomically important pest.

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.

The African planthopper Leptodelphax maculigera (Hemiptera: Delphacidae) has been recently reported in many places in Brazil in association with maize. Its occurrence in maize production fields in Brazil has brought concerns to the corn production chain regarding the possibility of this planthopper to be a vector for maize bushy stunt phytoplasma (MBSP), corn stunt spiroplasma (Spiroplasma kunkelii), maize rayado fino virus (MRFV), and maize striate mosaic virus (MSMV). The phytoplasma and spiroplasma, which are bacteria belonging to the class Mollicutes, and the two viruses are associated with the corn stunt disease complex. Given the presence of the African planthopper species and the corn stunt complex in Brazil, we further investigated the abundance of this planthopper species in the State of Santa Catarina, Brazil, and whether the planthopper can carry the four pathogens. We inspected 12 maize production fields in different municipalities in the state for 20 weeks, using two yellow sticky traps for each maize field. The sticky traps were replaced weekly. A total of 130 specimens of L. maculigera were captured, with a great discrepancy in quantity among locations and weeks. We detected the mollicute MBSP and the viruses MRFV and MSMV in L. maculigera, whereas S. kunkelii was absent in the assessed African planthopper samples. The molecular detection of the phytoplasma and the viruses in field-collected African planthoppers is strong evidence that this insect species has the ability to acquire those pathogens through feeding from the phloem of diseased maize plants. Nonetheless, transmission capacity needs to be experimentally proven to assert L. maculigera as a vector for the corn-stunting pathogens.

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. 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. 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.

ABSTRACTDalbulus maidis (Hemiptera: Cicadellidae) is the primary pest of corn crops in Brazil due to its high efficiency in transmitting pathogens associated with the corn stunt disease complex, including maize bushy stunt phytoplasma (MBSP) and corn stunt spiroplasma (CSS), as well as maize rayado fino virus (MRFV) and maize striate mosaic virus (MSMV). However, many aspects of the behaviour and bioecology of this insect vector are still poorly understood. Accordingly, we investigated the escape behaviour of D. maidis at three different times of the day (6:00 a.m., 1:30 and 6:00 p.m.) under controlled conditions. This behaviour was compared between sexes and among populations of healthy leafhoppers and those carrying bacteria that cause corn stunt diseases (phytoplasma and spiroplasma). The studies were conducted in November/2022 (first crop season conditions) and April/2023 (second crop season conditions). Groups of 100 leafhoppers (50 males and 50 females), healthy or infected with phytoplasma or spiroplasma, were placed in cages containing maize plants. Following the application of mechanical disturbances, the number of individuals that left the maize plants was recorded. Temperature positively influenced the escape behaviour of D. maidis. Moreover, a higher proportion of leafhoppers abandoned maize plants under conditions that simulated the first crop season (27.3%) than the second crop season (14.3%). This propensity was consistently higher during the hottest period of the day (1:30 p.m.). Meanwhile, infected leafhoppers were less active than healthy leafhoppers under the second crop season conditions and lower average temperatures. No differences were observed in escape behaviour between the sexes. The behaviour of D. maidis observed in this study supports the recommendation of applying insecticides during the cooler hours of the day, which may enhance their effectiveness against this insect vector. Similarly, field sampling involving direct insect counts on maize plants is also recommended under these same conditions.

The incidence of maize stunt diseases, or achaparramiento , rose in Nicaragua from an insignificant level to national crisis proportions, then declined to insignificant levels again, all in the space of 10 yr. The 3 pathogens that cause achaparramiento, corn stunt spiroplasma, maize bushy stunt phytoplasma, and maize ray ado fino virus are transmitted by the corn leafhopper, Dalbulus maidis (De- Long & Wolcott). Vector populations did not change sufficiently over time to explain the epidemic pattern. Nor did changes in the varieties of maize that farmers used cause the differential expression of disease symptoms during this period. The most likely explanation of the epidemic pattern is an abrupt 3- to 4-yr increase in irrigated maize production during the dry season, when maize was not grown traditionally. Irrigated maize provided a temporal bridge for the pathogens, which then were transmitted to rainy season plantings and caused epidemic disease incidence throughout the country. This explanation demonstrates the powerful impact that governmental agricultural policies, in this case to strongly promote dry-season maize production, can have on crop pest and pathogen problems.

The corn leafhopper, Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae) is broadly distributed throughout the American continent, from southeastern and southwestern USA to Argentina. It is the most important leafhopper pest of maize, Zea mays L., in Latin America (Nault 1990), and causes great losses to corn crops because of its capacity to transmit efficiently corn stunt spiroplasma (CSS), maize bushy stunt phytoplasma (MBSP), and maize rayado fino virus (MRFV) (Nault & Ammar 1989). Egg parasitoids are the most important natural enemies of leafhoppers (Freytag 1985). The known egg parasitoids of D. maidis comprise 4 taxa of Mymaridae, 4 of Trichogrammatidae, and 1 Eulophidae (Table 1), but none of these are known in Mexico, putative corn leafhopper origin center (Nault 1990). In the laboratory, 6-10 females of D. maidis, which were 2 weeks old and obtained from Zapopan site, were placed in polyethylen-terephtalathe (PET) cylindrical cages (35 cm high × 18 cm diam.) on maize leaves in order to obtain sentinel eggs. Potted maize plants (pot of ca. 10 dm) in the vegetative stage (3 to 5 leaves) were checked daily for eggs. Twice, on 17 Aug and 23 Aug, 10 plants containing less than 24-h-old eggs were exposed in each site during 72-96 h. Potted plants containing sentinel eggs were placed inside the cornfield at no more than 3 m from the edge of the field. Sentinel eggs of D. maidis were exposed to parasitization in 2 cornfields in Jalisco State from Aug to Sep, 2008 at Zapopan site (20°44’40.2”N, 103°30’48.3”W, elevation 1,662 m), and El Grullo site (19°47’50.4”N, 104°12’43”W, elevation 869 m). After 8 to 10 d, the leaves containing exposed eggs were cut from the plant in the laboratory and transferred to a petri dish with the bottom containing wet tissue paper and covered with clear plastic food wrapping to avoid desiccation, and to keep wasps from escaping. Parasitized eggs were checked daily to ensure leaf quality until the emergence of the adult wasps. The parasitization rates were not measured due to rotting or desiccation of some leaves containing exposed eggs.

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.

Corn stunt disease is a major limiting factor in production of corn (Zea mays) in the Americas. To develop a polymerase chain reaction (PCR) assay specific for detection of the causal agent, Spiroplasma kunkelii, PCR primers were designed on the basis of unique regions of the nucleotide sequence of the S. kunkelii spiralin gene. DNA was amplified in PCRs containing template DNAs derived from laboratory strains of S. kunkelii and from naturally diseased corn plants collected in the field. No DNA amplification was observed in PCRs containing template DNAs derived from other Spiroplasma species tested or from healthy corn or corn infected by maize bushy stunt phytoplasma. The availability of a sensitive and specific PCR for detection and identification of S. kunkelii should facilitate studies of the ecology of this pathogen, as well as its influence in the incidence, spread, and severity of corn stunting diseases.

There is a behavioral difference between male and female of insect vectors of plant pathogens that may reflect on the transmission of such pathogens. Dalbulus maidis is the leafhopper vector of the maize bushy stunt (MBS) phytoplasma. In this work, sex ratio of D. maidis collected directly from the maize whorl or with yellow sticky cards in a field plot in Piracicaba, SP (Brazil) was evaluated during the first month of the crop development. The natural MBS infection of the captured leafhoppers was assessed by PCR and the disease incidence was visually evaluated in the maize plots. Female D. maidis were more easily captured from the maize whorl, whereas male leafhoppers were more abundant in the cards. The incidence of MBS diseased plants in the plot was 21.2%. MBS phytoplasma was detected in 8% of the captured females whilst 2% of males carried the prokaryote. It is possible that the infected leafhoppers in the early stage of the crop contribute to the final disease incidence. Additionally, the acquisition and transmission rates to maize seedlings by males and females of D. maidis, virgin or mated, was studied. Acquisition rate of MBS phytoplasma was not significantly different between male and female leaf hoppers, however, female, either virgin or mated, transmitted the phytoplasma in a higher rate than males. The behavior of females of spending more time on the plant feeding may explain the higher natural infection of MBS phytoplasma in field condition and the increased transmission rate observed in the experiment.

Background and Aims Maize bushy stunt phytoplasma (MBSP) is a bacterial pathogen of maize (Zea mays L.) across Latin America. MBSP belongs to the 16SrI-B sub-group within the genus ‘Candidatus Phytoplasma’. MBSP and its insect vector Dalbulus maidis (Hemiptera: Cicadellidae) are restricted to maize; both are thought to have coevolved with maize during its domestication from a teosinte-like ancestor. MBSP-infected maize plants show a diversity of symptoms. and it is likely that MBSP is under strong selection for increased virulence and insect transmission on maize hybrids that are widely grown in Brazil. In this study it was investigated whether the differences in genome sequences of MBSP isolates from two maize-growing regions in South-east Brazil explain variations in symptom severity of the MBSP isolates on various maize genotypes. Methods MBSP isolates were collected from maize production fields in Guaíra and Piracicaba in South-east Brazil for infection assays. One representative isolate was chosen for de novo whole-genome assembly and for the alignment of sequence reads from the genomes of other phytoplasma isolates to detect polymorphisms. Statistical methods were applied to investigate the correlation between variations in disease symptoms of infected maize plants and MBSP sequence polymorphisms. Key Results MBSP isolates contributed consistently to organ proliferation symptoms and maize genotype to leaf necrosis, reddening and yellowing of infected maize plants. The symptom differences are associated with polymorphisms in a phase-variable lipoprotein, which is a candidate effector, and an ATP-dependent lipoprotein ABC export protein, whereas no polymorphisms were observed in other candidate effector genes. Lipoproteins and ABC export proteins activate host defence responses, regulate pathogen attachment to host cells and activate effector secretion systems in other pathogens. Conclusions Polymorphisms in two putative virulence genes among MBSP isolates from maize-growing regions in South-east Brazil are associated with variations in organ proliferation symptoms of MBSP-infected maize plants.

Simple SummaryPhytopathogenic bacteria such as phytoplasmas induce physiological changes in their host plants that may modulate the behavior of an insect vector in favor of their own spread. In this study we investigate changes in the host selection behavior of the leafhopper vector, Dalbulus maidis (DeLong and Wolcott), in choice tests between healthy vs. maize bushy stunt phytoplasma (MBSP)-infected maize leaves (Zea mays L.), for insects previously exposed to infected plants (named “bacteriliferous”) or not (naive). The results showed that males and naive females of D. maids did not distinguish the treatments when infected leaves were still asymptomatic, whereas bacteriliferous females prefer to settle on healthy leaves, a behavior that favors pathogen inoculation and primary spread at early crop stages. During the symptomatic phase of maize infection, naive males and females were initially attracted to infected leaves, favoring pathogen acquisition; interestingly, the females tend to move towards healthy leaves a few hours later, a behavioral shift that promotes secondary spread. Overall, this study presents evidences that MBSP optimizes its spread in maize crops by influencing the host selection behavior of the leafhopper 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.