Mario A. Urías-López

Influence of Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury on Yield of Different Types of Maize

Abstract Two field experiments were conducted in 1995–1996 to determine if there are common yield responses among maize hybrids to larval western corn rootworm, Diabrotica virgifera virgifera LeConte injury. Three yellow dent hybrids, five white food grade dent hybrids, and a popcorn hybrid were included in the study. The minimum level of rootworm injury as measured by root damage ratings (3.2–4.2) that significantly reduced yield was similar across the hybrids included in the study. However, the pattern of yield response to different rootworm injury levels varied among hybrids. This suggests that maize hybrids may inherently differ in their ability to tolerate rootworm injury and partition biomass in response to injury and other stresses. The complex interaction among hybrid, level of injury, and other stresses suggests that a common western corn rootworm injury–yield relationship may not exist within maize.

Influence of Western Corn Rootworm (Coleoptera: Chrysomelidae) Larval Injury on Photosynthetic Rate and Vegetative Growth of Different Types of Maize

Abstract Two field experiments were conducted in 1995–1996 to determine if there are common photosynthetic and vegetative growth responses among genotypes of maize, Zea mays L., to larval western corn rootworm, Diabrotica virgifera virgifera LeConte injury. Specific variables measured from rootworm infested and noninfested plants were midday leaf photosynthetic rate, plant growth stage, and plant height during 9–18 leaf growth stages. Three yellow-dent hybrids, five white food-grade dent hybrids, and a popcorn hybrid were included in the study. Results suggest that there may be a common negative photosynthetic response within maize to larval injury during vegetative growth stages. Transient reductions in photosynthetic rate occurred in rootworm infested maize at both low to moderate levels of root injury, which after a lag period, led to significant reductions in plant height. This trend was consistent across hybrids in both experiments during each year. Plant growth stage was not significantly affected by rootworm injury during vegetative periods.

Abundancia Temporal de la Escama Blanca del Mango, Aulacaspis tubercularis Newstead 1 , en Guerrero, México

Resumen. La escama blanca del mango, Aulacaspis tubercularis Newstead, es una plaga emergente de importancia económica en México, debido a que daña el follaje y ramas de árboles de mango, así como la apariencia de frutos destinados a exportación y mercado nacional. Conocer la fluctuación poblacional de una plaga y su relación con los factores climáticos que regulan sus poblaciones es importante para implementar medidas de control. Durante el primer y segundo año de monitoreo se encontraron diferencias significativas en la abundancia de las poblaciones de A. tubercularis en las distintas fechas de muestreo, con picos poblacionales de colonias y total por hoja de escama en mayo y agosto durante el primer año de monitoreo, mientras que en el segundo año, los picos poblacionales de colonias, hembras y total por hoja de escamas, ocurrieron en junio, julio, agosto, diciembre, enero, y febrero, respectivamente. Aunque A. tubercularis, se distribuyó en todas las ramas de los árboles de mango orientadas hacia los cuatro puntos cardinales, las poblaciones fueron más abundantes en el lado sur y norte. Se encontró que la temperatura y el viento se correlaciona positivamente con la abundancia de A. tubercularis, mientras que la precipitación y humedad relativa se correlacionan negativamente.

Sweetpotato Whitefly (Homoptera: Aleyrodidae), Aphid (Homoptera: Aphididae) Populations, and Complex of Viruses in Watermelon on Different Planting Dates in Jalisco, Mexico

Abstract The goals of this study were to determine the population dynamics of sweetpotato whitefly, Bemisia tabaci (Gennadius); green peach aphid, Myzus persicae (Sulzer); and the cotton/melon aphid, Aphis gossypii Glover, as well as to explore the incidence of the complex of aphid-borne viruses of watermelon, Citrullus lanatus L., on different planting dates. Four (1998–1999) and six (1999–2000) watermelon plots were monitored under grower management conditions in La Huerta and Casimiro Castillo, Mexico. Plant growth, sweetpotato whitefly, and aphid (adult and nymph) populations, and percentage of virus-infected plants were measured in fall–winter watermelon plots planted at different dates. The population of sweetpotato whitefly varied significantly by planting date and showed two different population patterns. Watermelon planted in early October had higher population density at young developmental stages, whereas plantings from mid-October had more adults at flowering or harvesting. Aphid species may be present at any time in fall–winter watermelon. However, higher levels of infected plants and more damage caused by viruses occurred when watermelon was planted on 16 November or later. Several factors acting separately or interactively may influence the population dynamics of vector populations and the complex of viruses in watermelon. Current levels of vector populations (nymphs) may not be high enough to produce direct damage to watermelon plants, but adults may be important factor in the viruses’ infection process. Planting before mid-November may aid in getting lower levels of infected plants and improving yield.