Corn Leafhopper Research Articles

Dry season parasitoids of adult corn leafhoppers (Hemiptera: Cicadellidae) on irrigated maize in Mexico

AbstractParasitoids of adult corn leafhoppers, Dalbulus maidis (DeLong et Wolcott), were studied in irrigated maize (Gramineae) growing during the dry season in Mexico. Dalbulus maidis was parasitized by Metadorylas spinosus (Hardy) (Diptera: Pipunculidae), Halictophagus naulti Kathirithamby et Moya-Raygoza (Strepsiptera: Halictophagidae), and Gonatopus bartletti Olmi (Hymenoptera: Dryinidae) at 24 of the 54 sites where D. maidis were collected. Greater rates of parasitism occurred at higher elevations (R2 = 0.41) and at more southern latitudes (R2 = −0.52). Metadorylas spinosus is a previously unreported parasitoid of D. maidis, and this is the first report of H. naulti parasitizing Dalbulus elimatus (Ball) and Dalbulus gelbus DeLong. Gonatopus bartletti has the broadest geographic and temporal distribution of the parasitoids found.

Management of corn leafhopper (Homoptera: Cicadellidae) and corn stunt disease in sweet corn using reflective mulch.

Plastic reflective mulches significantly reduced populations of corn leafhopper, Dalbulus maidis (DeLong & Wolcott), adults and the incidence of corn stunt disease caused by Spiroplasma kunkelii (CSS) in late planted sweet corn (Zea mays L.). The reflective mulches were more effective than were either foliar or soil applied insecticides in managing both the leafhopper and the pathogen it transmits. Yields of marketable ears were 1.5 to 2 times greater in reflective mulch plots than from fallow plots. This was due to larger ears (individual ear weight and length) rather than an increase in the number of ears. The use of reflective mulches provides an alternative strategy to insecticides in the management of both D. maidis and corn stunt disease. Such a strategy may prove useful to growers in Latin America and to limited resource growers and organic growers in the United States who wish to grow corn without the use of insecticides.

<I>Halictophagus naulti</I> sp. n. (Strepsiptera: Halictophagidae), a New Species Parasitic in the Corn Leafhopper (Homoptera: Cicadellidae) from Mexico

A new species of Strepsiptera Halictophagus naulti (Halictophagidae) that is parasitic in the corn leafhopper Dalbulus maidis (Delong & Wolcott) from the Mexican state of Morelos is described.

Aspectos biológicos de Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) em híbridos de milho (Zea mays L.)

Alguns aspectos da biologia da cigarrinha do milho, Dalbulus maidis (DeLong & Wolcott), foram estudados em seis híbridos de milho contrastantes quanto à resistência a esse inseto, selecionados em ensaios conduzidos no campo. O experimento foi realizado em casa de vegetação a 26,0 ±4,9°C e 78,8±6,8% de UR. Utilizando-se microgaiolas, dez ninfas por híbrido foram diariamente observadas, anotando-se o número de ínstares e o período de desenvolvimento. Nos adultos obtidos mediram-se o comprimento do corpo, a largura do abdome e a distância entre os olhos compostos. Entre os híbridos avaliados, somente o Pioneer 3027 prolongou significativamente o período de desenvolvimento das ninfas, em cerca de três dias. Não houve diferença significativa entre os híbridos quanto ao número de ínstares e tamanho do corpo dos adultos.

Transmission Biology of Maize Bushy Stunt Phytoplasma by the Corn Leafhopper (Homoptera: Cicadellidae)

Effects of temperature and vector age at the time of acquisition on the transmission of maize bushy stunt phytoplasma by the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), were studied. Mean latent period in the leafhopper and transmission rate of the Tlaltizapan maize bushy stunt phytoplasma isolate had a quadratic relation with temperature. Mean latent period was inversely related to temperature from 15 to 25°C. Transmission rate was highest at 20 and 25°C and lowest at 15 and 30°C. The Tlaltizapan isolate was transmitted better when maize bushy stunt phytoplasma was acquired as nymphs than as adults at 15, 20, and 25°C. The transmission biology of 3 maize bushy stunt phytoplasma isolates by D. maidis was compared when leafhoppers acquired phytoplasma as nymphs and were held at 15 and 25°C. Differences among the 3 isolates were found only at 25°C. At this temperature, the Poza Rica isolate had a longer mean latent period and higher transmission rate than the El Batan and Tlaltizapan isolates. Moreover, the Poza Rica isolate had a longer incubation period in the plant host and produced more basal tillering in infected maize than did the other 2 isolates. Based upon biological findings in this study, as well as molecular studies reported elsewhere, we propose that maize bushy stunt phytoplasma has a polyphyletic origin and evolved from strains of the aster yellows phytoplasma.

Amostragem e abundância de cigarrinhas e danos de Dalbulus maidis (DeLong & Wolcott) (Homoptera: Cicadellidae) em plântulas de milho

Em levantamentos de cigarrinhas em milho (Zea mays), sorgo (Sorghum bicolor) e área em pousio, o número de movimentos de rede, entre 5 e 20 vezes por 10 m de linha, não afetou significativamente o número de insetos coletados. Dalbulus maidis (DeLong & Wolcott) foi a espécie mais comum entre as cigarrinhas coletadas em plântulas de milho (93%), sorgo (40%) e nas áreas em pousio (34%). A espécie Peregrinus maidis (Ashmead) foi a menos abundante nos três ambientes estudados. A cigarrinha-do-milho, D. maidis, foi coletada mais eficientemente através da amostragem individual de plantas, usando-se o método do saco de plástico, do que com o uso da rede entomológica. Para determinar os danos de D. maidis, um, cinco e 10 adultos/planta foram confinados em plântulas com 10 e 15 dias de idade, durante uma semana. Em plântulas com 15 dias não se verificou efeito significativo. Por outro lado, em plântulas com 10 dias observou-se uma relação quadrática da densidade de infestação com o peso seco da parte aérea e do sistema radicular. No nível máximo de infestação utilizado, 10 adultos/planta, observou-se perdas de 40% no peso seco da parte aérea e de 62% no peso seco do sistema radicular.

Morphology of the Digestive and Reproductive Systems of Dalbulus maidis and Graminella nigrifrons (Homoptera: Cicadellidae)

The corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Homoptera: Cicadellidae) is the principal vector of maize rayado fino marafivirus, corn stunt spiroplasma and maize bushy stunt phytoplasma in tropical and subtropical areas of the Western Hemisphere. The black-faced leafhopper, Graminella nigrifrons (Fobes) (Homoptera: Cicadellidae) is the principal vector of maize chlorotic dwarf waikavirus in North America. The morphology of their digestive and reproductive systems was studied by light microscopy, and illustrations were made to aid in dissection and injection of pathogenic inoculum for various vector-pathogen relation studies. In both species, two salivary glands, located one on each side of the head, extend into the mesothorax. Each gland consists of principal and accessory glands. The former contains an anterior lobe and posterior lobe. Two types of acini are present in the anterior lobe, whereas the posterior lobe has four acini. The accessory glands of D. maidis and G. nigrifrons are very similar rod to elbow-shaped structures. The esophagus of both species is a narrow tube originating from the pharynx and extending to the anterior midgut below the filter chamber. The anterior midgut is a large sac-like structure extending from the metathorax through the entire length of the abdomen, and then ascends backward to the anterior of the midgut to form the filter chamber. The filter chamber of D. maidis has a more complex structure than that of G. nigrifrons. There are two pairs of Malpighian tubules in both species. The central tubule is formed from a pair of fused tubules within the filter chamber; the other tubules extend along the front of the hindgut. In G. nigrifrons the three tubules run parallel to each other along the top of the posterior midgut. In D. maidis, the central tubule and one tubule from the other pair run along the interior of the deep loop of the posterior midgut; the other tubule runs along the exterior of the loop. The ovaries of both species contain six ovarioles. Each ovariole consists of a terminal filament, a germarium, developing oocytes and eggs within follicles and a pedicle. The ovarioles contain six follicles. In G. nigrifrons each ovariole usually contains only one egg within the last follicle whereas the ovarioles of D. maidis often contain two eggs. The ovarioles open into the lateral oviduct, common oviduct and the vagina. The spermathecae open into the common oviduct. A collaterial gland and accessory glands are present. The male of both species has two lateral testes each with six follicles. A pair of accessory glands arise at the posterior of each seminal vesicle and open into the lateral ejaculatory duct.

Enzymatic oxidation products of allelochemicals as a basis for resistance against insects: effects on the corn leafhopper Dalbulus maidis.

Oxidation products of com allelochemicals generated by peroxidases or tyrosinases were tested in 10% sucrose solutions for effects on the corn leafhopper Dalbulus maidis. Some reduction in feeding was noted with hydrogen peroxide (a cofactor for peroxidase). Significant reduction in feeding was noted with chlorogenic acid, ferulic acid, p-coumaric acid, and 6-methoxybenzoxazolinone (MBOA), but not rutin at 400 ppm in solution. Oxidation products of these compounds all caused significantly less feeding by the leafhoppers compared to the original compound. Oxidation products generated by peroxidase from ferulic acid and 6-methoxybenzoxazolinone caused significant mortality to the leafhoppers within 5 days. Thus, provided conditions are such that oxidizing enzymes and allelochemicals can interact due to damage by insects, resistance may be significantly enhanced by the oxidized products as opposed to the effects of the allelochemicals alone.

Epidemic Roller Coaster: Maize Stunt Disease in Nicaragua

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.

Movement and Multiplication ofSpiroplasma kunkeliiin Corn

After the introduction of Spiroplasma kunkelii into the leaves of corn (Zea mays) seedlings by inoculative corn leafhoppers (Dalbulus maidis), the pathogen was detected by enzyme-linked immunosorbent assay. Spiroplasmas were detected in leaves 14 days after exposure to inoculative leafhoppers (as much as 2 weeks before symptoms appeared) and in roots after 20 days. The probabilities of detecting spiroplasmas in different plant organs, determined by logistic regression, generally increased over time ; the probability was greater in roots than in leaves at most testing dates. Spiroplasmas moved into tassels as they developed. The age and/or size of the plant at the time of infection affected pathogen movement ; spiroplasmas were detected earlier in roots of plants inoculated at the one-leaf seedling stage than in those of plants inoculated at the four-leaf stage. Spiroplasma titers remained relatively low in all the plants until the third or fourth week after inoculation. After that time, populations in different plant samples varied within a large range, and the upper limit of the range generally increased with time. The maximum titers were reached earlier in plants inoculated at the four-leaf stage than in plants inoculated at the one-leaf stage. Because S. kunkelii may be present in various plant organs well before symptoms appear, spiroplasmas might be acquired by leafhoppers before disease is obvious in the field.

Use of a Biotinylated DNA Probe for Detection of the Aster Yellows Mycoplasmalike Organism in Dalbulus maidis and Macrosteles fascifrons (Homoptera: Cicadellidae)

A DNA probe was used to detect aster yellows mycoplasmalike organism acquisition by the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), an insect that does not transmit aster yellows mycoplasmalike organism, as well as by Macrosteles fascifrons (Stœl), a vector insect. Results show the effectiveness of the probe for pathogen detection in both the non-vector and the vector insect.

Inoculation and acquisition of maize bushy stunt mycoplasma by its leafhopper vector Dalbulus maidis

SummaryMaize bushy stunt mycoplasma (MBSM), a mycoplasma‐like organism, is transmitted in a persistent manner by the corn leafhopper, Dalbulus maidis, to maize (Zea mays). The influence of the duration of acquisition access and inoculation access periods on the transmission of MBSM by D. maidis was investigated. The proportion of plants infected by D. maidis increased significantly from 0 to 0.51 as the inoculation access time to a plant increased from 10 min to 72 h (X2= 101.5, P < 0.001). Likewise, the proportion of insects acquiring MBSM from infected plants increased from 0 to 0.19 as the acquisition access time to the source plant increased from 10 min to 72 h (X2= 53.2, P < 0.001). The data were fitted to a loglinear regression model. No significant association was found between the sex of the insects and vector ability.

Seasonal Polyphenism of Adult Dalbulus Leafhoppers (Homoptera: Cicadellidae)

Leafhoppers from Mexico in the genus Dalbulus exhibit significant seasonal differences in overall body size and coloration as measured by dry body weight, wing length, and intensity of pigmentation. In the laboratory, the corn leafhopper, Dalbulus maidis (DeLong & Wolcott) and its close relatives, the Mexican corn leafhopper, D. elimatus (Ball); D. gelbus DeLong; the fivespotted gamagrass leafhopper, D. quinquenotatus DeLong & Nault; and the Eastern North American species, Baldulus tripsaci Kramer & Whitcomb were reared from egg to adult under environmental conditions typically found in Mexico during the wet growing season (young seedlings at 28:20°C and a photoperiod of 14:10 [L:D] h) and beginning of the dry winter (mature plants at 23:17°C and a photoperiod of 12:12 [L:D] h). Adults reared under environmental conditions that simulated the beginning of the dry Mexican winter were, on average, 8% larger, 29% heavier, and, except for B. tripsaci , 25% darker in pigmentation than adults reared under conditions typical of the wet summer growing season. Field-collected Dalbulus adults also showed seasonal variation in size and color. Dalbulus species, which specialize on maize ( Zea mays L.), generally exhibited greater seasonal variation in color and size than those that specialize on perennial gamagrasses ( Tripsacum spp.). Seasonal increase in body size most likely indicates greater storage of energy for survival of harsh conditions and possible migration, whereas variation in color may be an adaptation with thermoregulatory and cryptic benefits.

Influence of developmental conditions on cold‐hardiness of adult Dalbulus leafhoppers: implications for overwintering

AbstractLittle is known about how adults of the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), and its congeners survive subfreezing temperatures at high elevations during the dry winter in Mexico. In the laboratory, duration of survival at −5 °C was measured for four Mexican Dalbulus species: D. maidis, D. elimatus (Ball), D. gelbus DeLong and D. quinquenotatus DeLong & Nault; and a closely related North American species, Baldulus tripsaci Kramer & Whitcomb. Adult leafhoppers reared under environmental conditions that simulated the beginning of the dry winter season during October in Mexico (‘October‐reared’) were at least twice as tolerant of −5 °C than adults reared under environmental conditions that simulated the beginning of the wet summer season during June (‘June‐reared’). Dalbulus species found primarily at high elevations, such as D. elimatus, were seven times more tolerant of −5 °C than D. quinquenotatus, a species which overwinters at low to mid elevations on its Tripsacum hosts. October‐reared D. maidis adults survived relatively short periods at −5 °C (LT50 = 8.9 h) compared to October‐reared D. elimatus adults (LT50 = 42.3 h). This suggests that in Mexico, D. maidis either overwinters in protected habitats at higher elevations or it migrates to lower, frost‐free regions. October‐reared B. tripsaci adults, which overwinter in the egg stage, were intolerant of −5 °C (LT50 = 2.6 h). A conditioning period for 1 h at +5 °C before and after exposure to −5 °C significantly improved survival for D. maidis. Supercooling points (SCPs) were between −23 and −20 °C, indicating that mortality of these leafhoppers at −5 °C was due to cold shock injury rather than internal ice formation.

Overwintering Biology of Dalbulus Leafhoppers (Homoptera: Cicadellidae): Adult Populations and Drought Hardiness

Despite the economic importance of the corn leafhopper, Dalbulus maidis (DeLong & Wolcott), little is known about how this maize pest and its congeners survive the dry winter in Mexico. In the field, Dalbulus populations were monitored weekly with yellow sticky card traps for 18 mo at three sites in Jalisco, Mexico. The sites included a maize field, Zea maysL. ; a natural stand of a perennial teosinte, Zea diploperennis Iltis, Doebley & Guzman; and a natural population of gamagrasses, Tripsacum spp., which are maize relatives. At all sites, highest catches of Dalbulus adults occurred during the dry season between October and March. In a laboratory study to test the survival of adult Dalbulus leafhoppers without their host plants, significant differences were detected among leafhopper species. When denied all food and water (absolute drought), Dalbulus species that specialize on maize were more tolerant than those that specialize on gamagrass. Adults reared under environmental conditions that simulate the beginning of the wet season (June-reared) were less tolerant of absolute drought than adults reared under early dry-season conditions (October-reared). When provided water but no food, October-reared D. maidis lived significantly longer than June-reared D. maidis . Survival of females under water-only conditions was significantly longer than that of males. Field observations revealed that gamagrass-specializing D. gelbus DeLong and D. quinquenotatus DeLong & Nault overwinter as continuously developing populations on their hosts. In contrast, our data indicate that D. maidis overwinter as active adults that can subsist, at least in part, on free water in the absence of host plants until the summer rainy season begins. Surviving adults then migrate locally to newly planted maize fields.

Evaluation of Two Leafhopper Sampling Methods for Predicting the Incidence of a Leafhopper-Transmitted Virus of Maize

Two sampling methods for estimating the abundance of corn leafhopper, Dalbulus maidis Delong & Wolcott, were evaluated for predicting the incidence of maize rayado fino virus (MRFV), a virus transmitted to maize in a persistent manner by D. maidis . Leafhoppers were sampled weekly using both counts of insects on plants and yellow sticky traps in maize planted at two densities, and the incidence of MRFV was recorded twice during that period. There were fewer leaf 110 ppersper plant, a lower incidence of MRFV, and fewer virus-infected plants per square meter in maize planted at a higher density, but there were no differences in the number of leafhoppers caught per trap or in the number of leafhoppers per square meter. Multiple regression analysis revealed that the number of leafhoppers per plant was a reliable predictor of disease incidence, but no relationship between trap catch and disease incidence could be detected. These results suggest that counts of vectors on plants may be more reliable than sticky traps for predicting the incidence of persistently transmitted plant pathogens.

Vegetational Diversity, Ants (Hymenoptera: Formicidae), and Herbivorous Pests in a Neotropical Agroecosystem

The effect of vegetational diversity on ants and herbivores was studied in a maize-bean (Zea mays-Phaseolus vulgaris) biculture and a maize monoculture in Nicaragua. Three basic hypotheses were examined: (1) the abundance of herbivores on maize would be less in the biculture than in the monoculture, (2) ant foraging activity would be higher in the biculture, and (3)the effect of ants as natural enemies of maize pests would account for differences in the abundance of those pests in the bicultures. The effects of plant diversity on the abundance of Spodoptera frugiperda (J. E. Smith), the fall armyworm, and Dalbulus maidis (De Long & Wolcott), the corn leafhopper, were examined. Ant-foraging activity was estimated as the proportion of tunafish baits occupied by ants in monocultures and bicultures. The effect of ants on the maize herbivores was investigated by excluding ants through selective poisoning. Cropping patterns significantly influenced the numbers of fall armyworm and corn leafhopper, but in different ways. The corn leafhopper was more abundant in bicultures, and the fall armyworm was more abundant in monocultures. No significant difference was found in the proportion of baits occupied by ants in maize monocultures and maize- bean bicultures. Ants had a significant effect on the two main maize pests, S. frugiperda and D. maidis . There were significantly higher numbers of both pests in plots where ant foraging activity was reduced with insecticide. These results suggest the possibility of using ants as agents of biological control in the maize agroecosystem in Nicaragua.

Host plant dispersion, leaf hopper movement and disease transmission

Abstract. The plant‐to‐plant movement of the corn leafhopper, Dalbulus maidis Delong & Wolcott, and the spread of the leafhopper‐borne maize rayado fino virus were investigated in four patterns of maize (Zea mays) dispersion. D. maidis was less abundant and the spread of the virus was slower in dense stands of maize than in sparse stands. When plant density was held constant, leafhoppers were more abundant in maize stands with relatively equidistant plant spacing (uniform dispersion) than in stands with densely‐sown rows (linear dispersion) or double‐sown hills (clumped dispersion), but there was no difference in virus incidence among these plant dispersion patterns. Leafhoppers were less likely to move to adjacent plants in uniform plant dispersion patterns than in either linear or clumped dispersion patterns. This result may explain the lack of higher virus incidence in uniform stands, despite higher leafhopper abundance. Leafhopper movement was consistent with a simple rule: the shorter the distance to the next adjacent plant, the more likely a leafhopper is to move between plants. These results demonstrate that host plant dispersion can affect the abundance and behaviour of highly mobile herbivorous insects even when plant density is constant.

Ants (Hymenoptera: Formicidae) as Natural Control Agents of Pests in Irrigated Maize in Nicaragua

The effect of the natural ant community as a possible source of biological control for the fall armyworm, Spodoptera frugiperda (J. E. Smith), and the corn leafhopper, Dalbullus maidis (De Long & Wolcott), was examined in irrigated maize, Zea mays L., in the Pacific plains of Nicaragua. By means of poison baits, ant-foraging activity was reduced in plots planted with maize and compared with control plots. Ants were found to significantly reduce fall armyworm and corn leafhopper abundance as well as damage by the fall armyworm to maize plants. The results are discussed in relation to establishing economic injury levels for the fall armyworm in irrigated maize and the possibility of incorporating ants as a component of an integrated pest management program on maize in Nicaragua.

EUDORYLAS (METADORYLAS) SP. (DIPTERA: PIPUNCULIDAE): A PREVIOUSLY UNREPORTED PARASITOID OF DALBULUS MAIDIS (DELONG AND WOLCOTT) AND DALBULUS ELIMATUS (BALL) (HOMOPTERA: CICADELLIDAE)

The genus Dalbulus (Homoptera: Cicadellidae) consists of 11 species, 10 of which can be found in México (Nault 1990). Some members in the genus, such as the corn leafhopper, Dalbulus maidis (DeLong and Wolcott), and the Mexican corn leafhopper, Dalbulus elimatus (Ball) are serious pests of maize due to their transmission of three corn stunting pathogens: corn stunt spiroplasma (CSS; Spiroplasma kunkelii Whitcomb et al.), maize bushy stunt mycoplasmalike organism (MBSM), and maize rayado fino virus (MRFV) (Nault 1990). Due to the widespread damage that these leafhopper-vectored pathogens cause in maize-growing regions in Latin America, a search for the leafhopper natural enemies was conducted in maize agroecosystems in central México.