Laboratory populations of the sweet potato whitefly, Bemisia tabaci, have been shown to consist of both migratory and trivial flying morphs. The behavior of these forms as part of the process of short-range migration was examined under field conditions. Insects were marked in a field of melons using fluorescent dust during two consecutive growing seasons. During the first growing season, passive traps used to collect living whiteflies, were placed along 16 equally spaced transects radiating from the field to a distance of up to 1.0 km. Wind out of the north-east consistently carried migrating whiteflies to traps placed along transects in the south-western quadrant because cold air drainages dictate wind direction during early morning hours in the desert South-west. For this reason, during the second season traps were laid out over fallow ground in a rectangular grid extending 2.7 km to the south-west of the marked field. If dispersal was entirely passive, patterns could be described using a diffusion model. Statistical examination of the data, howèver, demonstrated that the distribution on all days was patchy. Geostatistical techniques were used to describe the observed patchiness. Traps in the immediate vicinity of the marked field caught more whiteflies than the daily median. Large numbers were also collected from near the periphery of the grid. White-flies were far less prevalent in the grid's center. As a result, the distribution of captured whiteflies can be described as bimodal. These patterns confirm behavior observed in the laboratory, i.e., a portion of the population are trivial fliers that do not engage in migration and are consequently captured in traps near the field, and a portion initially respond to cues associated with skylight, ignoring cues provided by the ground, and fly for a period of time before landing in distant traps. During both years movement out of the field had an exaggerated directional component on 13 of 14 days.

A total of 108 pectolytic, soft-rotting Erwinia strains were collected from 11 types of cacti growing in Arizona, Texas, northern Mexico, and Australia between 1958 and. Four strains were collected from soils beneath or close to naturally rotting saguaro cacti. Collectively, these strains caused soft rots of saguaro, organ pipe, and senita cacti, Opuntia (cactus) fruits and pads, tomato fruits, and potato slices, but only occasionally caused soft rots of slices of carrot roots. A numerical cluster analysis showed that 98 of the 112 strains formed a uniform group (cluster 1A) that was distinguished from other pectolytic erwinias by an API 20E code of 1205131, by negative reactions in API 5OCHE tests for L-arabinose, myo-inositol, D-cellobiose, melibiose, and D-raffinose, and, in supplemental tests, by positive reactions for malonate and growth at 43°C. The average levels of DNA relatedness of 22 cluster 1A strains to the proposed type strain (strain 1-12) as determined by the hydroxyapatite method were 88% in 60°C reactions (with 1% divergence within related sequences) and 87% in 75°C reactions. The levels of relatedness to the type strains of other Erwinia spp. were 138% in 75°C reactions. Cluster 1A strains also had a characteristic cellular fatty acid profile containing cyclo-( 11,12)-nonadecanoic acid (C19:o cycle cll-lz) and missing tridecanoic acid (CI3J, heptadecanoic acid (C1,:o), and cis-9-heptadecenoic acid (Cl,:l g ) , which separated them from other pectolytic erwinias. Collectively, these data indicate that the members of cluster 1A are members of a new species, which we name Erwinia cacticida. Three cactus strains in cluster 1B appear to represent a second new species that is closely related to E. cacticida; these strains are designated E . cacticida-like pending the availability of additional strains for testing. The remaining cactus strains (in cluster 4) have the physiological, DNA, and fatty acid profiles of Erwinia carotovora.To our knowledge, Johnston and Hitchcock (22) were the first workers to describe a bacterial soft-rot disease of cacti in the United States. The cultures of these authors were isolated from prickly pear cacti (Opuntia tomentella Berger and OpuntiaJicus-indica (L.) Mill.) that were originally from Guatemala and Columbia but were growing in the U.S. Department of Agriculture plant introduction garden in Florida. The bacterium was briefly characterized as "an actively motile, gram-negative, aerobic, and facultative anaerobic bacillus" which produced an acid reaction when it was grown in broth containing "glucose, saccharose, mannite, and salicin but none in maltose, lactose, dulcite, and arabinose" (22). Subsequently, another new bacterial species, Erwinia carnegieana Standring 1942 (23), was described (3, 6, 23, 28) as being the causal agent of bacterial necrosis (a soft-rot disease) of saguaro cacti (Carnegiea gigantea Britt. & Rose). Among the soft-rot erwinias, this species was unique in that it was gram positive, a characteristic also noted by Boyle (6), and had a host ...

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Aspergillus flavus isolates from Arizona can be divided into S and L strains on the basis of sclerotial morphology. These genetically distinct strains differ in aflatoxin production. To help understand factors influencing the aflatoxin producing potential of A. flavus communities, spatial and temporal patterns of strain incidence were compared with patterns of A. flavus propagule density in Yuma County soils. Strain S isolates were found in all sampled fields, but the percentage of strain S isolates ranged from 4 to 93%. A nested analysis of variance was used to determine the spatial scale at which most variability in strain composition and propagule density occurred. For both variables, the largest component of variance occurred among fields within areas at a spatial scale of 1 to 5 km. There was also spatial structure (12 to 21% of the variance) at the subregional level (> 20 km) in strain composition, but not in propagule density. Temporal patterns for both variables were similar. The sampling periods with the highest incidence of strain S isolates, August 1994 (60%) and July 1995 (62%), occurred during cotton boll formation. The regional average for A. flavus propagule density was near 1000 propagules/g in the summer, but less than 100 propagules/g in the spring. The results suggest that insights into factors influencing the toxigenicity and propagule density of A. flavus communities might be achieved most readily by contrasting fields in close spatial proximity.

Annual census data spanning seventy-five years document mortality and regeneration in a population of saguaro cactus (Carnegiea gigantea) in the Cactus Forest of the Rincon Mountain District of Saguaro National Park near Tucson, AZ. On 6 four-hectare plots, each saguaro was censused and a methodical search for new saguaros was conducted annually each year from 1942 through 2016, with the exception of 1955. Regeneration has been episodic with 828 plants established from 1959 through 1993 compared with 34 plants established between 1942 and 1958 and only three plants established after 1993. The years preceding 1959 and following 1993, include some of the driest decades in centuries in southern Arizona. While woodcutting and cattle grazing are believed to be among the causes of decades of failed regeneration prior to 1958, neither of these factors contributed to the failed regeneration following 1993. The height structure of the population from 1942 to 2016 shifted dramatically from a population dominated by large saguaros (> 5.4 m tall) in the first three decades of the study to a population dominated by small saguaros (< 1.8 m tall) in the most recent two decades. Mortality is shown to be strongly age dependent. In the year following the 2011 catastrophic freeze, 21 of 59 plants older than 80 years died compared with zero deaths in 270 plants between the ages of 29 and 80 years. Saguaros under 40 years old, growing under small shrubs or in the open, have a lower probability of survival than better protected saguaros. Long-term population monitoring is essential to understanding the complex impacts of human and environmental factors on the population dynamics of long-lived species.

No abstract

Aspergillus flavus is a soil-inhabiting fungus that frequently produces aflatoxins, potent carcinogens, in cottonseed and other seed crops. A. flavus S strain isolates, characterized on the basis of sclerotial morphology, are highly toxigenic. Spatial and temporal characteristics of the percentage of the A. flavus isolates that are S strain (S strain incidence) were used to predict patterns across areas of more than 30 km(2). Spatial autocorrelation in S strain incidence in Yuma County, AZ, was shown to extend beyond field boundaries to adjacent fields. Variograms revealed both short-range (2 to 6 km) and long-range (20 to 30 km) spatial structure in S strain incidence. S strain incidence at 36 locations sampled in July 1997 was predicted with a high correlation between expected and observed values (R = 0.85, P = 0.0001) by kriging data from July 1995 and July 1996. S strain incidence at locations sampled in October 1997 and March 1998 was markedly less than predicted by kriging data from the same months in prior years. Temporal analysis of four locations repeatedly sampled from April 1995 through July 1998 also indicated a major reduction in S strain incidence in the Texas Hill area after July 1997. Surface maps generated by kriging point data indicated a similarity in the spatial pattern of S strain incidence among all sampling dates despite temporal changes in the overall S strain incidence. Geostatistics provided useful descriptions of variability in S strain incidence over space and time.

Genetic structure of Phytophthora infestans, the causal agent of potato and tomato late blight, was analyzed spatially in a mixed potato and tomato production area in the Del Fuerte Valley, Sinaloa, Mexico. Isolates of P. infestans were characterized by mating type, allozyme analysis at the glucose-6-phosphate isomerase and peptidase loci, restriction fragment length polymorphism with probe RG57, metalaxyl sensitivity, and aggressiveness to tomato and potato. Spatial patterns of P. infestans genotypes were analyzed by geographical information systems and geo-statistics during the seasons of 1994-95, 1995-96, and 1996-97. Spatial analysis of the genetic structure of P. infestans indicates that geographic substructuring of this pathogen occurs in this area. Maps displaying the probabilities of occurrence of mating types and genotypes of P. infestans, and of disease severity at a regional scale, were presented. Some genotypes that exhibited differences in epidemiologically important features such as metalaxyl sensitivity and aggressiveness to tomato and potato had a restricted spread and were localized in isolated areas. Analysis of late blight severity showed recurring patterns, such as the earliest onset of the disease in the area where both potato and tomato were growing, strengthening the hypothesis that infected potato tubers are the main source of primary inoculum. The information that geostatistical analysis provides might help improve management programs for late blight in the Del Fuerte Valley.