Aerial dispersal of European red mites (Acari: Tetranychidae) in commercial apple orchards

Aerial dispersal of European red mite, Panonychus ulmi (Koch), in commercial apple orchards was estimated by trapping windborne mites. Studies were conducted at four orchards in eastern New York during 1989 and 1990 and at three orchards in western New York during 1989. In each orchard mites were trapped in three locations; the interior of the orchard, at the border of the orchard and in a field or woodlot beyond the orchard. Large numbers of mites were captured, even when the numbers of mites on apple foliage were well below levels where mite injury to leaves was visible (less than five per leaf). The log numbers of mites trapped were linearly related to the log density of mites on leaves and this relationship was consistent for each year and region the study was conducted. The trap captures among the three locations in and outside an orchard were highly correlated. The implications these findings may have on metapopulation dynamics and resistance to acaricide dynamics are discussed.     

Replant problems in South Tyrol: role of fungal pathogens and microbial population in conventional and organic apple orchards

The South Tyrol, the main apple-growing area in Italy, is characterised by intensive soil cultivation. Previous investigations have revealed the existence of replant disorders although the main causes of these have not been evaluated. A survey was carried out in this area with two main aims: to evaluate the role of soil-borne pathogens in apple replant disease and to compare the impact of organic and conventional management on replant diseases caused by soil-borne pathogens. The experimental sites were chosen to obtain three pairs of contiguous conventional and organic apple orchards. There was a high level of organic matter in both the organic and the conventional apple orchards with no appreciable differences in humic fractions. The soil sickness test with apple seedlings revealed a significant reduction in growth for all soil samples as compared to the peat control. The growth score on soil samples from organic orchards was significantly higher than that obtained on conventional soil. Total fungal population in soil samples was positively correlated to the apple seedlings growth score and negatively correlated to the frequency of root colonisation. Most of the root-colonising pathogens belonged to the well-known root rot complex, Rhizoctonia solani and Pythium spp. being the most pathogenic on apple seedlings.     

Seasonal changes in zooplankton abundance in the lower Rhine during 1987–1991

Zooplankton in the River Rhine was surveyed for five years at the Dutch sampling stations, Lobith (German/Dutch border) and Maassluis (at the point of discharge of the river into the North Sea). The zooplankton abundance showed an apparent seasonal pattern at both stations, characterized by low densities during the winter period, and higher densities during the summer period, with a spring peak. Zooplankton was dominated by rotifers at both stations, although during the winter periods the contribution of copepods was considerable. The rotifers were dominated byBrachionus angularis, B. calyciflorus, Keratella cochlearis andK. quadrata; the copepods by cyclopoid nauplii; the cladocerans by small-sized species mainly belonging toBosmina. At Maassluis the relative contribution of copepods was higher than at Lobith. Furthermore, the zooplankton at Maassluis included the speciesEurytemora affinis, characteristic for estuarine conditions. In spring, the rotifer density and water temperature and rotifer density and chlorophylla concentration were positively correlated. Furthermore, both rotifer density and chlorophylla were inversely correlated with discharge. The possible role of environmental factors (water temperature, chlorophyll content, discharge and biotic factors) controlling the river zooplankton dynamics is indicated.     

Dynamics of potentially harmful microalgae in a confined Mediterranean Gulf—Assessing the risk of bloom formation

The population dynamics of potentially harmful microalgae was investigated in the semi-enclosed shallow Gulf of Kalloni, Greece (Aegean Sea, Eastern Mediterranean), during a 2-year period from August 2004 to March 2006. A total of 21 potentially harmful microalgae (bloom-forming and/or toxic) were identified including 3 diatoms and 18 dinoflagellates. The densities of each species were analyzed in time and space and in relation to environmental parameters. Some species such as Alexandrium insuetum, Heterocapsa circularisquama, Karlodinium veneficum, Scrippsiella trochoidea, and Ceratium spp. developed high cell concentrations, particularly during a Pseudo-nitzschia calliantha winter bloom. Other species such as Dinophysis caudata, Ostreopsis ovata, Prorocentrum minimum, and Protoperidinium crassipes were rare or appeared in small numbers. Densities of the most abundant species were closely associated with freshwater nutrient-rich inputs during winter, being negatively correlated with temperature and salinity and positively correlated with nitrogen. The spatial distribution of the abundant species exhibited a marked increase towards the inner part of the gulf, close to the main freshwater inputs, whereas some species were mainly concentrated in the dilute surface layer (1 m depth). Examination of the abundance–occupancy relationship revealed that the species more prone to bloom are those with wide spatial distribution and frequent presence throughout the year such as the diatom P. calliantha. Although blooms of cyst-forming species are rarer, an increased risk can be foreseen under favorable resource supply and environmental conditions during winter.     

Home gardens in western Nepal: opportunities and challenges for on-farm management of agrobiodiversity

Home gardens are defined as a system of production of diverse crop plant species, which can be adjacent to household or slightly further away and is easily accessible. Species composition and management systems of Nepalese home gardens are poorly known. The study was conducted to develop an inventory on composition of crop species and varietal diversity to characterise the home gardens of Rupandehi and Gulmi of western Nepal, and to observe the species change over the time for last 10–15 years. Semi-structured Interviews, Direct Observation and Focus Group Discussions were employed to collect primary data. Shannon–Weaver index (SWI) was used to determine the species richness. Principal Component Analysis (PCA) was employed to characterise the home gardens. Mid-hill SWI (H′ = 4.41) revealed the higher species diversity (131 species) as compared to terai (123 species). This species richness was significantly higher (p = 0.001) in the mid-hill area. The vegetable species constitute the major component followed by fruits and fodder species that also contributed to the species diversity. The size of home gardens and species richness was positively correlated (r _s = 0.29, p = 0.001). Twenty crop species have been lost during the last 10–15 years and eleven species were threatened in the studied home gardens. Inaccessibility of local seed crops and deforestation were the major causes reported accounting for this trend. Self-saved seed was the major source of planting material in home gardens. There is a need to study the seed supply system for these home gardens. Therefore, a challenge is to make these home gardens self-supporting through creating a mechanism on strengthening local seed supply systems for long term sustainability of home garden in agrobiodiversity management.     

The parasitoid complex affecting Choristoneura rosaceana and Pandemis limitata in organically managed apple orchards

Parasitism and density of obliquebanded leafroller,Choristoneura rosaceana (Harris), and thethree-lined leafroller, Pandemis limitata(Robinson) (Lepidoptera: Tortricidae), were studied in 1998–2001 in organically managed apple orchards in the southern interior of British Columbia, Canada. The density of the overwintered generation of leafrollers in spring was significantly higher than thedensity of the first generation in summer. There was a significant inverse correlation between the density of leafrollers and the percent parasitism within generation and therefore parasitoids may play a role in controlling leafroller density. Parasitism of the overwintered generation (means between 5.5 and 24.7%) was significantly lower than parasitism documented in the summer generation (means up to 67.9%). The parasitoid complex recorded as emerging from these leafrollerpopulations in 1998–1999 included 30 species, of which eight have not been previously recorded in the literature as parasitoids of either leafroller species. The most frequently occurring parasitoids included Apophuasimplicipes (Cresson) and two species of Glypta(Hymenoptera: Ichneumonidae), Macrocentrus linearis (Nees), Meteorus trachynotus Viereck, Apantelespolychrosidis Viereck, Apanteles atra (Ratzeburg) and Microgaster epagoges Gahan (Hymenoptera: Braconidae), Colpoclypeus florus (Walker) and one Sympiesisspecies (Hymenoptera: Eulophidae). All of these more common parasitoids, except Glypta sp. 1 and M. epagoges, were recorded parasitizing leafroller hosts in both leafroller generations. The number of days to adult parasitoid emergence, when field collected parasitized hosts were held at 20°C, was recorded for four of the parasitoid species. Meteorus trachynotus was found to emerge early enough in spring toparasitize the few remaining overwintered early instar leafrollers. Glypta sp. 1, A. simplicipes and one Apanteles species emerged to coincide with the first generationin the summer.     

Evaluation ofMicrothrix inconspicuella, [Lepidoptera: Pyralidae], a potential biological control agent forEmex australis in Australia,carried out in apple orchards in South Africa

Host specificity tests carried out in the laboratory in Australia during 1977, showed thatMicrothrix inconspicuella Ragonot could develop on young apple leaves (Harley et al., 1979). Field studies in unsprayed apple orchards in South Africa showed that some feeding occurred, but fewer than 40% of late instar larvae developed to adults when confined in sleeves on apple tree branches. No feeding or survival occurred in large field cages or in the open. Adults which developed from apple fed larvae were smaller, deformed, occasionally mated and laid fertile eggs but their progeny did not feed or develop on apple fruit or leaves. In conclusion,M. inconspicuella larvae did not develop on apple fruit or leaves in the field, damage was mainly limited to apples already injured and feeding on leaves was minimal. Under normal pest control practicesM. inconspicuella populations did not survive on any part of the apple tree or onE. australis growing under the trees.      

Effects of water level changes and wading bird abundance on the foraging behaviour of blacknecked storks Ephippiorhynchus asiaticus in Dudwa National Park, India

The effect of water level changes and wading birds' abundance on the foraging behaviour of the blacknecked stork (BNS)Ephippiorhynchus asiaticus was studied from January 1995 to June 1997 in Dudwa National Park, Uttar Pradesh. Our observations indicate that BNS territoriality increased as food levels became depleted, resulting in increased rates of aggression towards intruders. Chasing or aggression was more intense during the early period (February and March) than the late period (April, May and June). Most of (> 50%) the aggressive encounters were observed between 0600 and 1000 h of the day. Seventeen species (including BNS) were observed interacting with BNS, throughout the study period. Most interactions were with the spoonbill,Platalea leucorodia (67.4%), followed by the whitenecked stork,Ciconia episcopus (16.6%). The distance (while foraging) between BNS and other wading birds varied significantly (P < 0001) between years indicating that BNS and other water birds foraged at different water depths and thereby explored the wetlands fully. Spoonbills were chased often; the number varied from 1 to 43 birds. BNS occasionally accepted the presence of other wading birds, including spoonbills and started foraging amidst them. This led to successful foraging of BNS (solitary feeder). Other fish-eating bird species and their numbers also limited the food consumption of foraging BNS as they had to spend time chasing away the intruders. Availability of the preferred prey fish species,Heteropnestus fossilis, forced BNS to stay throughout the year in their respective territories. High (> 60 cm) water levels were not suitable for BNS even though the patch had high prey abundance.     

Biological Control of Anastrepha spp. (Diptera: Tephritidae) in Mango Orchards through Augmentative Releases of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae)

Diachasmimorpha longicaudata (Ashmead) parasitoids were released by air on a weekly basis over 1600 ha of commercial mango orchards, backyard orchards, and patches of native vegetation, at a density of ca. 940 parasitoids/ha. Releases were made during 2 consecutive years, beginning at flower onset and lasting until the end of the production cycle. Two areas, 7 km apart, were compared. In one area parasitoids were released, whereas the other area was used as a control. During the 2nd year treatments were reversed. Fruit was sampled in commercial mango orchards and in backyard orchards to assess levels of parasitism in fruit fly larvae. Highly significant differences in percentage parasitism were found in release and control zones in backyard orchards. Furthermore, trapping results indicated that D. longicaudata releases were associated with ca. 2.7-fold suppression of Anastrepha spp. populations in backyard orchards. Results suggest that suppression might be affected by environmental conditions and by the parasitoid:fly ratio achieved. Anastrepha obliqua McQuart populations were suppressed more effectively by use of parasitoids than those of Anastrepha ludens Loew, perhaps due to the type of host fruits used by each species. Augmentative parasitoid releases in marginal areas surrounding commercial orchards (backyard orchards, wild vegetation) can substantially suppress fly populations. Through this approach, the number of flies that later move into commercial orchards can be significantly reduced. Such a strategy, when combined with sound orchard management schemes, can allow growers to produce clean fruit without the need to resort to the widespread use of insecticides.     

Host-parasitoid extinction and colonization in a fragmented prairie landscape

Few field studies of natural populations have examined the factors influencing local extinctions and colonization of empty habitat patches for a prey species and its predator. In this study, I carried out a census of planthopper (Prokelisia crocea; Hemiptera: Delphacidae) and egg parasitoid (Anagrus columbi; Hymenoptera: Mymaridae) incidence and densities in 147 host-plant patches (Spartina pectinata; Poaceae) over seven planthopper generations in a tall-grass prairie landscape. For both species, the likelihood of going extinct in a patch was related to a number of patch-specific variables: density, temporal variability in density, proportion of hosts parasitized (planthopper only), host-plant density, patch size, patch isolation, and composition of the surrounding matrix. Colonization likelihood was related only to the physical attributes of the patch. There was high patch turnover in this prairie landscape. On average, planthoppers went extinct in 23% of the patches and A. columbi went extinct in 51% of the patches in each generation. For the planthopper, extinction likelihood increased with a decrease in patch size and the proportion of the matrix composed of mudflat. Parasitism of eggs had no effect on the extinction likelihood of local P. crocea populations, suggesting that A. columbi may not play a major role in the patch dynamics of its host. The likelihood of extinction for A. columbi was dependent on factors that spanned three trophic levels. An increase in plant density, decrease in host density and decrease in parasitoid density all increased the likelihood of A. columbi extinction within a patch. The dependency on multiple trophic levels may explain the higher extinction risk for the parasitoid than its host. A. columbi extinction was also affected by the matrix habitat surrounding the patch—the effect was the opposite of that for P. crocea. Finally, vacant patches were colonized at rates of 53% and 34% per generation for the planthopper and parasitoid, respectively. For both species, colonization probabilities decreased with an increase in patch isolation. High host densities in a patch also favored high rates of colonization by A. columbi. I discuss how anthropogenic changes to the prairie landscape can affect the metapopulation dynamics and persistence time of this host-parasitoid interaction.     

Effect of native natural enemies on the population dynamics of the grape mealybug,Pseudococcus maritimus (Hom.: Pseudococcidae), in apple and pear orchards

The impact of native natural enemies on populations of the grape mealybug,Pseudococcus maritimus (Ehrhorn) in apple and pear orchards was assessed using a combination of techniques, including exclusion cages, limb-banding, and visual inspection of shoots and fruits. The complex of native natural enemies (which included two encyrtid parasitoids, (Pseudaphycus websteri Timberlake andMayridia species), a coccinellid beetle (Hyperaspis lateralis Mulsant), and a chamaemyiid fly (Leucopis verticalis Malloch), provided reasonably good control in orchards that had not been treated with insecticides for one to two years. However, surveys indicated that most of these species were absent from orchards regularly sprayed with pesticides.     

Interspecific interference between Apoanagyrus lopezi and A. diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

The parasitoids Apoanagyrus lopezi De Santis and A. diversicornis (Howard) (Hymenoptera: Encyrtidae) have been introduced into Africa for the biological control of the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae). We have studied competition between these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non-conspecific adult females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same time different numbers of non-conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each parasitoid were equal in all treatments.In both species, the presence of other foragers clearly affected several aspects of the parasitoids' behaviour. Patch residence time increased with the number of non-conspecifics in A. diversicornis. In both parasitoid species, the proportion of hosts left unparasitized after the patch visit decreased with increasing numbers of females on the patch. The proportions of super- and multiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more non-conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches. A. diversicornis produced offspring at a rate three times that of A. lopezi when one A. lopezi and one A. diversicornis foraged simultaneously. This is the first report of an aspect of interspecific competition where A. diversicornis has an advantage over A. lopezi. Interference between adult females thus promotes coexistence of the two species on P. manihoti.     

The association between the phytoplankton, Rhopalosolen species (Chlorophyta; Chlorophyceae), and Anopheles gambiae sensu lato (Diptera: Culicidae) larval abundance in western Kenya

Algae are important food resources of the larvae of the African malaria vectors, Anopheles gambiae Giles and Anopheles arabiensis Patton (Anopheles gambiae sensu lato), and other zooplankton, but empirical evidence remains meager about the agal flora in ephemeral water bodies. The animals present in natural aquatic habitats in western Kenya were sampled from July to November 2002 to study abiotic and biotic environmental factors determining A. gambiae sl larval abundance. The five highest concentrations of third and fourth instars and pupae (hereafter referred to as old-stage larvae) were sampled in conjunction with the unicellular epizoic green algae, Rhopalosolen species (Chlorophyta; Chlorophyceae). Canonical correspondence analysis revealed that the presence of Rhopalosolen species was the most important determinant of the animal assemblage. The density of old-stage A. gambiae sl larvae was positively correlated with the presence of Rhopalosolen species, but the density of first and second instars of A. gambiae sl was not. The water bodies with Rhopalosolen sp. yielded larger mosquitoes in spite of the higher density of larvae. We demonstrated that the productivity of water bodies in terms of the larvae of malaria vectors can differ in magnitude depending on the agal flora. We discuss phytoplankton as a regulator of mosquito larval populations.     

Population dynamics of Stylaria lacustris (Linnaeus, 1767) (Oligochaeta,Naididae) in Los Talas,Argentina

Population dynamics of Stylaria lacustris were analyzed over 2 years in a pond located at Los Talas, Argentina. In both years, the peak in abundance, due to intense asexual reproduction, fell at the end of winter, and was followed by mature individuals. The species was not collected during summer. Temperature was the main factor regulating the population through both sexual and asexual reproduction. In the second year, density was lower and correlated with a lower water level and a reduced vegetation development. Individuals were randomly distributed in periods of high abundance and contagious when density was low. Generation time was 15 days.     

First Quantitative Study of Rove Beetles in Oklahoma Winter Wheat Fields

Adult rove beetles (Staphylinidae) were sampled every 7–14 days from one winter wheat field located in each of the four major wheat growing regions of Oklahoma during the 1999–2000 and 2000–2001 growing seasons. The number of cereal aphids per tiller, wheat plant growth stage, and wheat tiller density also were estimated. A total of 12 genera representing 13 species of beetles were collected from the field. The density of rove beetles was generally low, ranging from 0.003 beetles per m² in fall to 0.106 beetles per m² in spring. Rove beetle communities differed among seasons. After accounting for the effect of season, there was no statistically significant association between rove beetle community structure and field location, aphid density, wheat plant growth stage, or wheat plant density. Most rove beetle species showed no association with a particular season, however, Aleochara notula Erichson, Lathrobium sp., and Oxypoda sp. were present predominantly in fall, while Bisnius inquitus Erichson was associated with winter. Oxypoda sp. was the most abundant rove beetle in winter wheat fields in spring and was relatively abundant in winter, but was not collected from wheat fields in fall. Tachyporus jocosus Say was present in wheat fields during all seasons. T. jocosus was the most abundant rove beetle species in the winter wheat fields in fall and winter and was the second most abundant species during spring.     

Relative developmental, environmental, and tree-to-tree variability in buds from field-grown apple trees

High-throughput genomic technologies are becoming more accessible to nonmodel plant species, and therefore, tissue collected outside controlled environments is being increasingly used for microarray analyses. In this study, we present a 15,720-feature apple microarray analysis of the variability of gene expression in buds from field-grown apple trees. Tree-to-tree and day-to-day variances were assessed during two different seasons: summer, when the meristems in the buds were undergoing the first stages of floral development, and autumn, when the buds were undergoing transition to winter dormancy. We found that apple trees with the same scion and rootstock cultivars, grown in a standard orchard environment, had small tree-to-tree variation. Gene expression differences caused by season was the dominant cause of variance while using false discovery rate control with a threshold of α* = 0.01 to select significantly different expression between genes. At this threshold, the environmental and location effects accounted for less than 10% of the genes selected. Consequently, we have shown that field microarray experiments are a viable approach for measuring seasonal changes in gene expression during apple bud development. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Information‐gathering as a response to manipulated signals in the eastern fence lizard,Sceloporus undulatus

Colorful visual signals are used across taxa to convey information during agonistic male‐male encounters, which are important for sexual selection. Although much is known about the information content of color signals, less is known about how receivers interpret this information. Here, using territorial Sceloporus undulatus lizards in a natural setting, we examined receiver response to intruders with different color patch sizes to determine (a) if patch size conveys information assessed during male‐male interactions and (b) if/how receivers modulate their behavioral responses to different types of behavioral signals. We found that larger lizards had longer and wider patches, indicating that the size of the patches may be one of the many characteristics of these patches that is used by males to convey information. Free‐ranging subject males also produced more headbob displays in response to intruders with small patches and took marginally longer to react to intruders with large patches. However, we found no differences in the aggressiveness of the response (i.e., fullshows). This indicates that patch size conveys information that is employed during territorial disputes, but that the response is primarily in terms of timing, allowing lizards to gather more information about intruders, instead of aggressive behavior (i.e., fullshows).