Tree Quadrants Research Articles

Pattern or process? Evaluating the peninsula effect as a determinant of species richness in coastal dune forests.

The peninsula effect predicts that the number of species should decline from the base of a peninsula to the tip. However, evidence for the peninsula effect is ambiguous, as different analytical methods, study taxa, and variations in local habitat or regional climatic conditions influence conclusions on its presence. We address this uncertainty by using two analytical methods to investigate the peninsula effect in three taxa that occupy different trophic levels: trees, millipedes, and birds. We surveyed 81 tree quadrants, 102 millipede transects, and 152 bird points within 150 km of coastal dune forest that resemble a habitat peninsula along the northeast coast of South Africa. We then used spatial (trend surface analyses) and non-spatial regressions (generalized linear mixed models) to test for the presence of the peninsula effect in each of the three taxa. We also used linear mixed models to test if climate (temperature and precipitation) and/or local habitat conditions (water availability associated with topography and landscape structural variables) could explain gradients in species richness. Non-spatial models suggest that the peninsula effect was present in all three taxa. However, spatial models indicated that only bird species richness declined from the peninsula base to the peninsula tip. Millipede species richness increased near the centre of the peninsula, while tree species richness increased near the tip. Local habitat conditions explained species richness patterns of birds and trees, but not of millipedes, regardless of model type. Our study highlights the idiosyncrasies associated with the peninsula effect—conclusions on the presence of the peninsula effect depend on the analytical methods used and the taxon studied. The peninsula effect might therefore be better suited to describe a species richness pattern where the number of species decline from a broader habitat base to a narrow tip, rather than a process that drives species richness.

Difference in the Abundance of Scale Insect Parasitoids Among Four Cardinal Directions

Summary We conducted a study to assess the potential differences in the abundances of hymenopteran parasitoids among cardinal directions. Experiments were conducted on scale insect-infested willow oak trees in the urban landscapes of South Carolina and Virginia. The parasitoids captured on yellow sticky cards deployed at the cardinal directions of the trees were identified and counted. We found that there were no significant differences in scale insect and parasitoid abundances among cardinal directions, and parasitoid abundances were weakly correlated with scale insect densities. The results suggest that 1 yellow sticky card could be deployed per tree, regardless of tree quadrant, to sufficiently sample for parasitoid abundance.

Medida indireta da clorofila e sua relação com o manejo da adubação nitrogenada em plantas cítricas fertirrigadas

O planejamento da programação nutricional na citricultura requer a avaliação da disponibilidade de nutrientes através de análises de solo e folha, e também leva em consideração a expectativa de produtividade e a exportação de nutrientes pela colheita. A disponibilidade de nitrogênio (N) não tem sido eficientemente avaliada através de análises do solo e, em algumas áreas de cultivo de plantas cítricas, o N-foliar vem sendo empregado como guia para recomendação de N. O objetivo deste estudo foi avaliar a sensibilidade da medida indireta da clorofila como um método de monitoramento dos níveis de N em plantas cítricas. Para isso, um trabalho experimental de campo foi conduzido em Reginópolis-SP, durante dois anos, com as variedades de copa Valência e Hamlim, ambas sobre porta-enxerto citrumelo Swingle. Os tratamentos consistiram em cinco doses de N aplicadas via fertirrigação: 0; 35; 70; 140 e 280 kg ha-1 de N, na forma de nitrato de amônio. Todas as parcelas foram devidamente fertilizadas com fósforo, potássio e micronutrientes também através da fertirrigação. A medida indireta da clorofila foi avaliada pelo clorofilômetro, modelo SPAD-502, em folhas recém-maduras (3ª e 4ª folhas), nos quatro quadrantes, e na altura mediana da planta. As mesmas folhas foram utilizadas para a determinação do teor de N-foliar. As medidas de leitura SPAD e o teor de N na folha apresentaram respostas quadráticas às doses de N aplicadas. Correlação de 0,95 (p < 0,05) foi observada entre a medida indireta da clorofila e o teor de N foliar. Durante os estádios de desenvolvimento da cultura, os valores médios de leitura SPAD variaram em 11 unidades, e os teores médios de N foliar, em 5 unidades (g kg-1). Leituras SPAD abaixo de 70 e acima de 75 estiveram relacionadas, respectivamente, com plantas muito responsivas e não responsivas a N, enquanto plantas com leituras intermediárias devem ser adubadas com doses de N próximas daquelas extraídas com a colheita. Baseado em duas safras completas, conclui-se que a medida indireta da clorofila pode ser empregada como ferramenta rápida e não destrutiva no monitoramento e na avaliação da disponibilidade de N em plantas cítricas

Seasonal Distributions of Eggs and Larvae of Rhagoletis indifferens Curran (Diptera: Tephritidae) in Cherries

The seasonal distributions of eggs and first-, second-, and third-instar larvae of the western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), in sweet cherries were determined at three sites in central Washington in 2002 and 2003. The egg was the major stage during early, mid and late season. The distributions of eggs (i.e., the percentages of total immature stages that were eggs) were similar all season, but those of first, second and third instars were greatest in late season. First, second and third instars occurred in similar numbers in 2002, but third instars were the most abundant in 2003. Tree quadrant had no effect on egg and larval densities and distributions. The majority of infested fruit had only one egg or larva, but there were significant increases in percentages of fruit with two or ≥ three eggs or larvae as percentages of fruit that were infested increased during the season. When there were two larvae in a fruit, one was larger than the other in 90.8% of cases. Results indicate time of season but not location within trees (1.5 to 2 m above ground) has differential effects on egg and larval distributions in fruit and on female oviposition behaviors that may result in multiple infestations and larval interactions. Seasonal effects on immature stages are probably related to developmental times and stage-specific mortality; whereas, effects on adults may be related to reduced availability of unoccupied fruit for oviposition.

Rates of population increase, abundance, and life stage distribution of Rhynchites cribripennis (Coleoptera: Attelabidae) on trees and in the soil in an olive grove.

The seasonal population abundance of Rhynchites cribripennis (Desbrochers) adults on olive trees was studied by collecting samples from an olive grove on the island of Zakynthos, Greece, from April 1994 to the end of July 1995. Moreover, the population abundance of larvae, pupae, and adults of R. cribripennis was recorded in soil samples from two soil depths (0-4 and 4-8 cm) from October 1994 to October 1995. Results showed that adult populations increased considerably on trees during May and June and peaked on 16 June (19.9 adults per twig) and 8 July (7.7 adults per twig) in 1994 and 1995, respectively. In 1994, no significant differences were found in the number of adults sampled from the different tree quadrants (northwest [NW], northeast [NE], southwest [SW], and southeast [SE]). However, in 1995, adult numbers in the NW quadrant of trees were significantly higher than those in the SE or SW quadrants. In soil samples, larvae were recorded throughout the sampling period with the highest numbers occurring in December, 2.4 larvae per soil sample, whereas pupae were found in lowest numbers in October and November. Adults were present in the soil samples from December to May, but the highest numbers were recorded in December, with a peak of one adult per sample. The number of adults was significantly higher, and that of larvae numerically higher, in the upper compared with lower soil layer, whereas pupae were found with similar numbers in both soil layers. Results of these studies suggest that this weevil exhibits a prolonged larval diapause and a 2-yr life cycle. The ecological implications of this behavior are discussed. Moreover, a prediction of the highest adult population on trees was estimated by taking into account the rate of increase of adult numbers in the early period of adult occurrence on trees.

Citrus Cutworm Insecticide Efficacy Trials, 1997

Abstract Two insecticide efficacy trials for the control of citrus cutworm were conducted in 1997. In the first experiment, three formulations of Bacillus thuringiensis were tested and compared with a water (check) spray in a commercial block of 32-year-old ‘Washington’ navel orange trees of Exeter Farms, Exeter, California. Applications of MYX 300, MYX 324, and CRYMAX WDG were made on 8 Apr using a Bean hand-sprayer at approximately 300 gpa, 300 psi. In the second experiment, two rates of RH-5992 70 WP and one rate of RH-2485 80WP, each combined with the surfactant Latron CS-7, and a treatment of Spinosad 2SC were compared to a water control spray in a block of 14-yr-old ‘Washington’ navel oranges at the Lindcove Research and Extension Center, Exeter, California. The applications were made on 11 Apr using the same equipment, rate, and pressure as the Exeter Farms test. In both experiments, eight replicated single-tree treatments were used and treatments were assigned on the basis on pre-treatment sampling of larvae. Larvae were collected by placing a canvas beating sheet (112 cm X 75 cm) beneath the outside foliage of the tree and vigorously shaking the foliage 10 times. Citrus cutworm larvae falling on the canvas were counted and recorded, then returned to the foliage. Pre-treatment larval counts involved sampling the Northeast and Southwest corners of the trees at Exeter Farms on 7 Apr and at Lind-cove on 4 Apr. All four tree quadrants were sampled for post-treatment larval counts on 15 Apr and 22 Apr at Exeter Farms; and on 18 Apr and 25 Apr at Lindcove.

Pre-harvest rindstain of ‘Valencia’ orange: histochemical and developmental characterization

Pre-harvest rindstain of California cultivar ‘Valencia’ orange has economic significance since fresh fruit marketability is reduced. Quantification of the incidence of rindstain as related to tree quadrant has allowed us to designate quadrants where rindstain was most likely to occur (upper outside SW) or least likely (lower inside NE) to occur. Growth and development characteristics of fruit from the two quadrants were measured throughout fruit development. Significant differences in percent weight loss between fruit from the SW and NE quadrants occurred at color break and at commercial maturity. Structural and histochemical changes in flavedo tissue of fruit from SW or NE tree quadrants were monitored over the course of fruit development and maturation. First evidence of periderm formation occurred in October, coincident with observed changes in histochemical staining for lipids. These differences were increasingly evident as the fruit approached horticultural maturity and visual symptoms of rindstain developed. The development of a pronounced periderm in affected fruit suggests that rindstain is due to a physical trauma, although we do not believe it is caused by wind.

Within-Orchard and Within-Tree Distributions of Peach Twig Borer (Lepidoptera: Gelechiidae) Damage to Peaches

The distribution of peach, Prunus persfca (L.) Batsch., fruit damage caused by the peach twig borer, Anarsfa lineatella Zeller, in orchards treated with pheromone dispensers for control of the oriental fruit moth, Grapholita molesta (Busck), was studied in four California peach orchards. Fruit damage in the tops of trees was significantly greater than fruit damage in the lower half of the tree canopy. Fruit damage at harvest was significantly greater than fruit damage at sampling dates up to 4 wk earlier in three of four orchards. Fruit damage in trees located on an orchard border was significantly greater than fruit damage in trees located in the center of the orchard. Fruit damage in trees located on the border row adjacent to an external source of A. lineatella was significantly greater than fruit damage in trees located in rows farther away from the external source. Fruit damage in the south tree quadrant was greater than fruit damage in at least one other tree quadrant in three of four orchards; this difference was significant in two of the three orchards. Results suggest that a simple fruit monitoring program can be used for peach orchards where control methods applied for other pests would not protect the crop from A. lineatella late in the season.

Distribution Patterns of Rhagoletis pomonella (Diptera: Tephritidae) Eggs in Hawthorn

The dispersion of eggs of the apple maggot fly, Rhagoletis pomonella (Walsh), among fruits sampled from two Crataegus mollis (Torr. et Gr.) Scheele hawthorn trees changed over the season, showing first an aggregated dispersion, subsequently a random dispersion, and finally an even dispersion. We suggest that eggs initially were aggregated because when host fruits were very hard and green (mid-August), females deposited eggs in the few sites that could be penetrated with the ovipositor. After the fruit ripened (September), eggs were dispersed evenly, suggesting that under conditions of abundant suitable fruits, females avoid ovipositing in fruit already containing an egg, probably in response to the host-marking pheromone deposited by females following egg-laying. As a result of the placement of eggs, most ripe fruits contained a single egg, thus larvae should have been assured ample developmental resources and minimal intraspecific interactions. Before fruit ripening, there were no significant distributional differences of eggs between the two trees or between the upper and lower half of the canopy. For the entire season, distribution among the tree quadrants was similar. As the season progressed, differences between the trees and crown levels within one of the trees appeared. We conclude that any dispersion study of a species that uses host discrimination cues should consider population density and comparative quality, quantity, and distribution of suitable available resources, as well as changes that may occur in these parameters over time.

Citrus Red Mite Pesticide Eficacy Tests in Riverside, 1986

Abstract Acaricides were tested for control of citrus red mite populations at Riverside, CA. A completely randomized design was used with 5 single-tree replicates per treatment. Trees were assigned to treatments based on pretreatment mite counts to minimize within-treatment variation. Applications were made on 15 Sep when mite densities were approaching the conventional treatment threshold of 2 adult females/leaf. Materials were applied with a handgun at 450 psi (cal 10 gal/tree, 1000 gpa) using a John Bean sprayer. Counts of live, adult female mites from one 5-leaf terminal per tree quadrant (total of 20 leaves/tree) were made 3 days following application and weekly thereafter until mite populations naturally declined due to the onset of cool temperatures in late Nov.

Citrus Red Mite Pesticide Efficacy Tests in Riverside, 1985

Abstract Acaricides were tested for control of citrus red mite populations in Riverside, CA. A completely-randomized design was used with 8 single-tree replicates per treatment. Trees were assigned to treatments based on precount densities to minimize within-treatment variation prior to the application of test materials. Applications were made on 22 and 23 Apr when mite densities were moderately high. Materials were applied with a handgun at 450 psi (ca 10 gal/tree, 1000 gpa) using a John Bean sprayer. Counts of live, adult female mites from two 4-leaf terminals per tree quadrant (total of 32 leaves per tree) were made weekly until mite populations naturally declined due to the onset of high (>37°C) daily temperatures in late May.

Development of Pheromone Trapping Techniques for Male San Jose Scale (Homoptera: Diaspididae)1

The effects of pheromone trap design and trap placement on collections of male San Jose scale, Quadraspidiotus perniciosus (Comstock), were studied over a 3-year period in California, Oregon, and Washington. Open (tent) trap designs were more efficient than closed traps, with small tent traps as good as larger tent traps. Trap placement in the north or east tree quadrants consistently produced the highest collections of male scale, but these catches are probably influenced by local meteorological conditions at the time of male flight. Collections of male scale increased as trap height increased into the upper tree canopy. Comparisons of the three pheromone isomers showed isomer SJS-3 generally to be more attractive than either SJS-1 or SJS-2. Pheromone dispenser load rates of 100 to 1,000 μg of SJS-2 showed no significant reduction in scale collections with 300- to 1,000-μg rates, compared with fresh 300-μg loads after 8 weeks of field exposure. Fresh, 300-μg loads were significantly better than all dispensers aged 16 to 19 weeks in the field

Relationship of Within-tree Placement of the Pheromone Trap to Codling Moth 1 Catches

Choice of pheromone trap location within the tree canopy has a significant effect on catches of the codling moth, Laspeyresia pomonella (L.). Trap elevation is the most important factor, followed by tree quadrant and placement relative to the periphery of the crown region. Along a vertical gradient, response was confined to traps within the canopy and catches increased with trap elevation. The effect of the trap position in the various tree quadrants on catch was of a lesser magnitude than trap elevation and generally less consistent. Overall, traps in the N quadrant caught ca. 30% less than in the other cardinal positions. Response to traps at the periphery of the crown region was not significantly higher than to traps near the center of the tree. Based on these findings, new guidelines for within-tree placement of pheromone traps are proposed. In addition, implications of this research for the direct control of the codling moth with pheromones using the male removal or the mating disruption technique are discussed.

SAMPLING METHODS FOR ESTIMATING THE ABUNDANCE AND DISTRIBUTION OF ALL LIFE STAGES OF THE APPLE MAGGOT, RHAGOLETIS POMONELLA (DIPTERA: TEPHRITIDAE)

AbstractSampling techniques for all life stages of the apple maggot, Rhagoletis pomonella (Walsh), were developed and their precision and accuracy evaluated. Reliable estimates were obtained for the egg and larval stages (standard error < 10%), but at the low population levels often encountered in the pupal and adult stages it was necessary to accept a lower level of precision (S.E. ≏ 25%). Eggs and larvae were uniformly distributed within trees. Variation between tree quadrants, and sections at different radii from the trunk, showed that stratification within trees was necessary for reliable estimation of the later stages. Predators acting in a heterogeneous environment under the trees were considered to be the major contributors to this variation. The most consistent source of variation was that between trees.