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.

The corn leafhopper, Dalbulus maidis (DeLong & Wolcott), is one of the most important pests of maize in Latin America because of its efficiency as a vector of 3 species of plant pathogens. In spite of its significance, however, little is known about its egg parasitoids. In this study, we present new data on D. maidis egg parasitoids in Mexico and Argentina. We surveyed the egg parasitoids in 2 locations: Mexico and Argentina, representing the farthest expansion of the D. maidis populations from Mexico. Using maize plants with sentinel eggs, parasitoids were surveyed in central Mexico and northwestern Argentina, at both low (1,000) elevation sites, during 2 maize-growing wet seasons. Parasitoids of the families Mymaridae and Trichogrammatidae were found in both countries. Argentinean sites showed the highest richness, with 10 species, whereas in Mexico we found 6 species. Also, the Shannon diversity index was 1.6 times greater in Argentina than in Mexico. Higher percentages of p... RESUMEN La chicharrita del maíz Dalbulus maidis es una importante plaga del maíz en América Latina, debido a su eficiencia como vector de tres especies de patógenos de plantas. A pesar de su importancia, el conocimiento sobre sus parasitoides de huevos es escaso. En este estudio, presentamos nueva información sobre los parasitoides de huevos de D. maidis en México y Argentina. Estudiamos los parasitoides de huevos de D. maidis en dos localidades: México y Argentina, que representa la distribución más lejana desde México. Los parasitoides fueron colectados utilizando plantas de maíz con huevos trampa, en el centro de México y noroeste de Argentina, en ambos lugares se monitorearon sitios de elevación baja (1.000), durante dos campañas agrícolas. En ambos países se registraron parasitoides pertenecientes a las familias Mymaridae y Trichogrammatidae. Los sitios de Argentina mostraron la mayor riqueza, con diez especies, mientras que en México se encontraron seis especies. Además, el indice d...

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.

Invertebrate herbivores prefer younger over older plant stages. Therefore, defensive traits against herbivores during early plant ontogeny are important. Defensive chemical and physical traits are well-studied in domesticated plants, but not in their wild relatives. Little is known about the function of trichomes, a physical defense against herbivore arthropods that damage cultivated plants and their wild ancestors. Maize is one of the most important crops in the world, but few studies have been conducted on the physical defenses during early ontogeny of maize and its wild relative teosinte. Therefore, the objective of this study was to characterize the density of trichomes (macrohairs) in maize and teosintes, and to evaluate the chewing damage by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) larvae on the 6-leaf stage of 1) perennial teosinte Zea perennis (Poaceae), 2) annual teosinte Zea mays ssp. parviglumis , 3) landrace maize, and 4) on the 2-leaf stage of the landrace maize. Significantly less damage occurred in both teosinte species, which showed pubescence (trichomes) on the upper leaf-blade, but not on the midrib leaf surface. The highest trichome density was found on Z. perennis , followed by Z. mays ssp. parviglumis at the 6-leaf stage. No trichomes were found on the landrace maize, at the 6-leaf stage or 2-leaf stage. Results suggest that trichomes play an important role in preventing damage by chewing larvae on the ancestors of maize. Genes that promote macrohair initiation in teosintes during early vegetative development could be incorporated into maize plants in the future.

Although the corn leafhopper Dalbulus maidis (DeLong and Wolcott) is the most important vector of maize pathogens in Latin America, little is known a

The corn leafhopper Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae) originated in Mexico, but is found from southeastern and southwestern USA to Argentina. Differences in reproductive and phenotypic traits between Mexican (native) and Argentinian (adventive) populations have been previously reported, but information on their genetic variation is currently unavailable. The objective was to investigate possible genetic variability among D. maidis populations collected in Mexico on maize and maize relatives (annual and perennial teosintes) and on maize in Argentina. A region of the mitochondrial gene coding for the cytochrome oxidase subunit I (mtCOI) and the ribosomal internal transcribed spacer (ITS2) were sequenced and analyzed. We developed the forward and reverse primers for the DNA amplification of COI in D. maidis (dalCOI). Twenty two and 17 sequences for dalCOI and ITS2, respectively, were generated and analyzed. No genetic variation among Mexican and Argentinian populations was... RESUMEN La chicharrita del maíz Dalbulus maidis (Delong & Wolcott) (Hemiptera: Cicadellidae) se originó en México pero se le encuentra desde el sur de los Estados Unidos de América hasta Argentina. Diferencias en la reproducción y caracteres fenotípicos entre poblaciones de D. maidis de México (nativas) y Argentina se han registrado previamente, pero se desconoce sobre su variación genética. El objetivo de este estudio fue investigar una posible variación genética entre poblaciones de D. maidis de México colectadas en maíz y sus parientes silvestres (teosintes anuales y perenes) y en maíz de Argentina. Una porción del gene mitocondrial que codifica para la subunidad 1 del citocromo oxidasa (mtCOI) y el espaciador interno transcrito del ADN ribosomal (ITS2) fueron secuenciados y analizados. En este estudio se desarrolló el cebador para la amplificación de COI en D. maidis (dalCOI). Veintidós y 17 secuencias para mtCOI y ITS2, respectivamente, fueron generados y analizados. No se observó variación genética ...