Studies on the biology and control of cavity spot of carrots

Using a selective medium of corn meal agar with pimaricin and rifamycin, isolations from asymptomatic periderm of carrots grown on experimental plots or in commercial crops most frequently yielded the fast-growing species Pythium intermedium, P. sylvaticum or P. ultimum. In contrast isolations from cavity spot lesions mostly produced the slow-growing species P. violae and P. sulcatum. Following treatment of crops with metalaxyl + mancozeb, few isolations from asymptomatic periderm produced Pythium spp. and generally there was a reduction in the number of cavities. Treatment had little or no effect on size distribution of cavities. Cavity spot incidence was significantly less at higher pH values, fields of pH 8·0 and above producing carrots with little or no disease.     

Detection of Pythium violae and Pythium sulcatum in carrots with cavity spot using competition ELISA

Conventional methods indicated that Pythium violae was most commonly isolated from carrot cavity spot samples from 14 UK sites. For one site the most frequently isolated species was Pythium sulcatum. Results of similar isolation work were compared with the assay of cavity spot lesions using polyclonal antibodies, raised to P. violae or P. sulcatum, in competition ELISA. Where lesions were artificially induced the test confirmed which pathogen was causal. With cavities developed on the field-grown carrots P. violae again predominated and the ELISA confirmed this. In one sample P. sulcatum was also isolated from a small number of lesions and was not detected in ELISA. The competition ELISA did not indicate presence of either Pythium in a range of non-cavity spot lesions from which attempts at isolation were negative.     

Cavity spot of carrots - observations on a commercial crop

A single field of commercially-grown carrots was sampled in September at 16 points for cavity spot incidence. Carrot tops, root core and peel were analysed for N, P, K, Ca and Mg, and soils were analysed for organic C, total N, available P, K, Ca, Mg and Na, pH, conductivity and chloride. The incidence of the disorder varied from 0–96% within a small area of field, thus tending to rule out explanations for cavity spot based entirely on weather, genotype etc. Several types of lesion were recorded in addition to ‘typical’ cavity spot, and their incidence was found to be mutually correlated. Most of these (including splitting) were positively correlated with cavity spot, and tended to be positively related to concentrations of macroelements in the carrot peel (especially N and Ca): however, ‘scabs’ were very strikingly dissociated from cavities (both on a plot and individual root basis). This dissociation appeared to be connected with soil pH, in that scabs were most common above pH 6-5, whereas cavities were most frequent below this pH.     

Projected Availability of Natural Cavities for Wood Ducks in Southern Illinois

Abstract: Wood ducks (Aix sponsa) and other species use tree cavities in forested wetlands and adjacent upland forests for nest sites and cover. The availability of tree cavities suitable for nesting is important to the population dynamics of hole-nesting species, but there is little quantitative information on how forest succession and maturation affect densities of suitable nest sites in eastern deciduous forests. Several studies have measured availability of tree cavities for nesting wood ducks, but data on cavity formation and persistence rates are needed to model changes in cavity abundance. We measured abundance and persistence of tree cavities suitable for nesting wood ducks in southern Illinois, USA, during 1993-2002. We simulated changes in abundance of nest cavities in the Mississippi River floodplain and adjacent upland forests using estimates of tree cavity densities by tree-diameter size classes and 10-year cavity persistence rates by tree species. Cavities were disproportionately common in the largest size classes, but tree species varied in their propensity to form cavities. Beech (Fagus grandifolia; 0.41 cavities/tree) and sycamore (Plantanus occidentalis; 0.50 cavities/tree) were prolific cavity producers, whereas a small proportion (0.05 cavities/tree) of cottonwoods (Populus deltoides) contained cavities. Kaplan-Meier estimates of annual and 10-year cavity persistence averaged 0.95 and 0.64, respectively. Cavity persistence also differed among species (P = 0.02): cottonwoods had the lowest (0.54) and sycamores had the highest (0.89) 10-year tree cavity persistence rates. Tree fall (50.0%), cavity floor deterioration (37.5%), and narrowing of the cavity entrance (12.5%) were the most prevalent causes of tree cavity loss. Forest stand projections indicated that cavity abundance will increase up to 34% over recent levels during the first 10 years and by 44% after 50 years. Most of this increase will be contributed by tree species that are not commonly used by wood ducks, but cavities will increase in oaks (Quercus spp.) and beeches as the forest matures into cavity-bearing size classes. Sycamores will steadily contribute cavities, but cottonwood is predicted to provide fewer cavities due to low survival of cavity-bearing size classes. Our results suggest that availability of nest and den sites for cavity-dependent wildlife will increase as eastern deciduous forests mature over the next half century. Cost-effectiveness of artificial nest box programs should be reevaluated in light of projected changes in tree cavity availability as deciduous forests mature in the eastern United States.     

Modelling damage on maize by the European Corn Borer, Ostrinia nubilalis

The European Corn Borer (ECB), Ostrinia nubilalis Hbn. (Lepidoptera: Pyralidae), is a major pest of maize in many countries. Yield losses caused by larvae of this insect depend mainly on the extent of cavity damage, the timing of tunnelling, and their within-plant distribution. To describe these factors, a mechanistic model of cavity appearance is proposed here. It takes into account the main biological processes which determine damage. These are the development, mortality and within-plant distribution of the ECB larvae. The model has been estimated and tested on field data collected at INRA-Versailles in France. Model fittings showed that (i) creation and lengthwise extension rates of cavities per larva depend on location and instar of the larvae, and that (ii) only instars 4 and 5 make cavities. This model described, with a high precision level, the appearance and lengthwise extension of cavities over time and their within-plant distribution for two maize varieties, several infestation dates and levels, and various climatic sequences.     

Nest cavity orientation in black‐capped chickadees Poecile atricapillus: do the acoustic properties of cavities influence sound reception in the nest and extra‐pair matings?

Birds that nest in cavities may regulate nest microclimate by orienting their nest entrance relative to the sun or prevailing winds. Alternatively, birds may orient their nest entrance relative to conspecific individuals around them, especially if the acoustic properties of cavities permit nesting birds to better hear individuals in front of their nest. We measured the cavity entrance orientation of 132 nests and 234 excavations in a colour‐banded population of black‐capped chickadees Poecile atricapillus for which the reproductive behaviour of nesting females was known. Most chickadees excavated cavities in rotten birch Betula papyrifera, aspen Populus tremuloides and maple Acer saccharum. Nest cavities showed random compass orientation around 360° demonstrating that chickadees do not orient their cavities relative to the sun or prevailing winds. We also presented chickadees with nest boxes arranged in groups of four, oriented at 90° intervals around the same tree. Nests constructed in these nest box quartets also showed random compass orientation. To test the acoustic properties of nest cavities, we conducted a sound transmission experiment using a microphone mounted inside a chickadee nest. Re‐recorded songs demonstrate that chickadee nest cavities have directional acoustic properties; songs recorded with the cavity entrance oriented towards the loudspeaker were louder than songs recorded with the cavity entrance oriented away from the loudspeaker. Thus, female chickadees, who roost inside their nest cavity in the early morning during their fertile period, should be better able to hear males singing the dawn chorus in front of their nest cavity. Using GIS analyses we tested for angular‐angular correlation between actual nest cavity orientation and the azimuth from the nest tree to the territories and nest cavities of nearby males. In general, nest cavity entrances showed no angular‐angular correlation with neighbourhood territory features. However, among birds who followed a mixed reproductive strategy and nested in the soft wood of birch and aspen trees, nest cavity entrances were oriented towards their extra‐pair partners. We conclude that nest cavity orientation in birds may be influenced by both ecological and social factors.     

Cavity construction by reintroduced populations of Red‐cockaded Woodpeckers (Dryobates borealis)

Although species reintroduction attempts are now common, monitoring of reintroduction attempts rarely extends beyond initial population establishment. This short timespan likely fails to document long‐term population stability, subtle changes in behavior, and the potentially larger effects that some reintroduced species may have on other species. The Red‐cockaded Woodpecker (RCW; Dryobates borealis) is an important habitat specialist and ecosystem engineer that excavates cavities in living trees. Excavation of natural RCW cavities can take years to complete, but they also persist for many years and are used by many other species. We quantified characteristics of cavity trees excavated by RCWs (n = 44) in two populations that were reintroduced to unoccupied areas more than 10 years earlier. We measured features associated with heartwood rot and used generalized linear mixed effects regression to determine whether these features differed for trees selected for cavity excavation compared with random neighboring trees. We also assessed population trends for cavity‐nesting species that commonly used RCW cavities on one of the sites. Height of first live limb was the only factor distinguishing natural RCW cavity trees from control trees. Four of six cavity‐nesting species monitored increased significantly following RCW establishment. The increases may relate to the many natural and artificial cavities created during the reintroduction effort. Future reintroductions of the RCW should lead to successful natural cavity excavation if sufficiently large trees with smaller live crowns are present. Future efforts may also benefit the broader community of cavity‐nesting birds.     

Percussive Foraging: Stimuli for Prey Location by Aye-Ayes (Daubentonia madagascariensis)

Aye-ayes (Daubentonia madagascariensis) use the thin middle finger to tap on wood in search of subsurface cavities containing insect larvae. When a cavity is located, they gnaw away wood until the prey can be extracted. Previous researchers suggested that acoustical cues reveal cavity location. We designed five studies to identify the cavity features that provide acoustical cues. When cavities were backfilled with gelatin or acoustical foam, excavation was still successful, suggesting that the reverberation of sound in air-filled cavities is not necessary for detection. Moreover, when the density of cavity content was varied, there was no difference in excavation frequency. On the other hand, a one-dimensional break in the subsurface wood was an effective stimulus for excavation. These studies suggest that a simple interface beneath the surface is sufficient to elicit excavation and that neither prey nor cavity nor even small air pockets are necessary to elicit the behavior. These results raise provocative questions as to how the aye-aye manages to forage efficiently.     

Selection of Nest Trees by Cavity‐nesting Birds in the Neotropical Atlantic Forest

One of the five most important global biodiversity hotspots, the Neotropical Atlantic forest supports a diverse community of birds that nest in tree cavities. Cavity‐nesting birds may be particularly sensitive to forestry and agricultural practices that remove potential nest trees; however, there have been few efforts to determine what constitutes a potential nest tree in Neotropical forests. We aimed to determine the characteristics of trees and cavities used in nesting by excavators (species that excavate their own nest cavity) and secondary cavity‐nesters (species that rely on existing cavities), and to identify the characteristics of trees most likely to contain suitable cavities in the Atlantic forest of Argentina. We used univariate analyses and conditional logistic regression models to compare characteristics of nest trees paired with unused trees found over three breeding seasons (2006–2008). Excavators selected dead or unhealthy trees. Secondary cavity‐nesters primarily selected cavities that were deep and high on the tree, using live and dead cavity‐bearing trees in proportion to their availability. Nonexcavated cavities suitable for birds occurred primarily in live trees. They were most likely to develop in large‐diameter trees, especially grapia Apuleia leiocarpa and trees in co‐dominant or suppressed crown classes. To conserve cavity‐nesting birds of the Atlantic forest, we recommend a combination of policies, economic assistance, environmental education, and technical support for forest managers and small‐scale farmers, to maintain large healthy and unhealthy trees in commercial logging operations and on farms.     

The relationship between introduced European Starlings and the reproductive activities of Mountain Bluebirds and Tree Swallows in British Columbia,Canada

The European Starling Sturnus vulgaris is an introduced species in North America and is an aggressive competitor for tree cavity nest‐sites. Starlings are commonly considered to influence nest‐site selection and reproductive success of native cavity‐nesting species negatively. We examined the relationship between Starling nest density and the fecundity of two native secondary cavity‐using passerines, Mountain Bluebird Sialia currucoides and Tree Swallow Tachycineta bicolor. We monitored a total of 622 nests (approximately equal numbers for each of the three species) in woodpecker‐excavated and naturally occurring cavities in 29 small forest groves in central British Columbia, Canada, between 2000 and 2009. The dimensions of cavities used and the timing of nest initiation overlapped for all species, although Starlings initiated clutches earliest. Mixed‐effects models were used to assess whether nest abundance, clutch size or nest success were affected directly by Starling nest abundance, or indirectly via a shift in cavity selection or timing of breeding. Starlings and Mountain Bluebirds showed inverse trends in nest abundance. Mountain Bluebird clutch sizes were smaller if they were initiated later in the breeding season. There was weak evidence that Tree Swallow clutch size decreased with cavity depth when Starling nests were abundant, and increased with cavity depth where there were few Starling nests. We conclude that despite the aggressive nature of this exotic cavity‐nester, the influence of Starlings on native secondary cavity‐nesting passerines is modest where cavities are abundant.     

The role of body size in nest-site selection by secondary cavity-nesting birds in a subtropical Chaco forest

Most bird species that nest in tree cavities globally occur in diverse assemblages in little-studied tropical and subtropical forests which have high rates of habitat loss. Conservation of these communities will require an understanding of how species traits, such as body size, influence nest-site selection. We examined patterns of nest-site selection of secondary cavity-nesting birds at the nest patch, tree and cavity scale, and investigated how these patterns are influenced by body size. Using conditional logistic regression, we compared characteristics of 155 nest tree cavities paired with 155 unused tree cavities in quebracho Schinopsis balansae forests in Chaco National Park, Argentina (2016–2018). The odds of a cavity being used for nesting increased with its depth and height above ground, decreased with entrance size, and were greater for dead trees than live. Small-bodied (13–90 g) species used floor diameters in proportion to availability, but medium- (150–200 g) and large-bodied (400–700 g) species selected cavities with larger floors. Model selection indicated that characteristics at the nest patch scale (canopy cover, tree density) had little effect on nest-site selection when cavity-scale variables were included. Cavity floor diameter, entrance size, cavity height and tree diameter (but not cavity depth) increased with body mass, and larger bird species more often used live trees. Two tree species proved to be key for the community: large and medium-sized birds used almost exclusively large live Schinopsis balansae, whereas small birds used live and dead Prosopis spp. in a proportion greater than its availability. Small birds could be differentiated according to species-specific cavity characteristics, but medium and large species overlapped considerably with one another. Although body mass explained much of the overall variation in tree and cavity characteristics between small and medium/large species, several small-bodied species consistently used cavities outside of the expected characteristics for their body size, suggesting that other natural history traits may play important roles in nest-site selection by small-bodied birds. To retain the full suite of secondary cavity-nesters in species-rich tropical and subtropical forests, it is necessary to conserve a diversity of trees and cavities that meet the full range of nesting requirements of these trait-diverse communities.     

Cavity selection for roosting,and roosting ecology of forest-dwelling Australian Owlet-nightjars (Aegotheles cristatus)

Abstract We compared a variety of attributes of tree cavities used for roosting by radio-tagged Australian Owlet-nightjars Aegotheles cristatus with randomly chosen prospective cavities to test which features are important for the species. Owlet-nightjars preferentially roosted in tree cavities closer to the ground, in trees with a significantly greater number of cavities and significantly closer to another tree with a cavity than expected by chance. There was also a significant interaction between cavity height and number of cavities in the tree. Tree size, decay stage and tree species were not statistically important cues used for making site choices. The requirements for Owlet-nightjars differ from those of most other Australian birds that use tree holes and also from most insectivorous bats. Telemetry data indicate that Owlet-nightjars move ～300 m between roost sites every 9 days on average. Individual birds used 2-6 different cavities during the 1–4-month period over which they were followed. The reasons for the relatively low levels of site fidelity are unknown.     

DEVELOPMENTAL ANATOMY OF SECRETORY CAVITIES IN THE MICROSPOROPHYLLS OF GINKGO BILOBA L.

Two to five secretory cavities develop in the hump region of the microsporophylls of Ginkgo biloba. A developing cavity is first recognized as a spherical pocket of large, densely cytoplasmic cells (central secretory cells) in the median portion of a microsporophyll primordium. These cells degenerate and a small cavity is formed which is filled with the contents of the degenerating cells. Flattened incurved cells (parietal secretory cells) develop around the disintegrating central secretory cells and slough off into the enlarging cavity. Thus, the cavities develop by lysigeny. A mature cavity is surrounded by senescent parietal secretory cells, scanty parenchyma, and a loosely fitting epidermis. Histochemical tests indicate the presence of lipid and pectic substances in the cavities. Previous reports on the morphological interpretation and possible function role of the cavities are discussed in the light of the present investigation.     

High Q Long-Range Surface Plasmon Polariton Modes in Sub-wavelength Metallic Microdisk Cavity

Metal-capped microdisk cavity supporting surface plasmon polaritons (SPP)-guided whispering gallery mode (WGM) can achieve higher cavity factor Q than traditional microdisk cavity in sub-wavelength dimensions. We have numerically analyzed the limiting factors on Q using finite difference time domain method. The Q of SPP-guided WGM is primarily limited by the loss of metal. A thin metal-sandwiched microdisk cavity supporting long-range surface plasmon polariton mode was proposed to reduce the metal loss. The proposed cavities have been shown to increase cavity Q by more than 15-fold and reduce threshold gain by more than threefold as opposed to traditional microdisk cavities.     

DEVELOPMENT OF BICELLULAR FOLIAR SECRETORY CAVITIES IN WHITE SNAKEROOT,EUPATORIUM RUGOSUM (ASTERACEAE)

Bicellular secretory cavities in Eupatorium rugosum occur only in foliar mesophyll, distributed uniformly from leaf tip to base, with a mean density of 450 per mm². They are absent from petiole and all other vegetative and floral organs. Each cavity contains an oily droplet, which is surrounded by two cup-shaped cells. An initial cell divides into two equal cavity cells with their shared wall always perpendicular to the epidermis. After vacuoles form, each protoplast retracts from the other and deposits a new, callosic wall around the cavity, and a thicker callose deposit on the remaining shared walls outside of the cavity. The original shared wall remains intact across the cavity until maturity. It is pulled taut by cavity cell growth and restricts further expansion except in one paradermal direction. Later, this shared wall disappears from the cavity. An oily fluid of unknown composition is secreted into the enlarging cavity. Because bicellular cavities develop neither lysigenously nor in true schizogenous fashion, we propose the term “pseudoschizogeny” for this type of development. Unusual, or perhaps unique, features of this cavity: bicellular condition, protoplast retraction from the common shared wall, and deposition of a callose wall. Preliminary results of a survey of Eupatorium show that bicellular cavities are uncommon but widely distributed geographically.     

Cavity use throughout the annual cycle of a migratory woodpecker revealed by geolocators

The importance of cavities as roost sites in migratory species is often unknown because it is challenging to monitor cavity use during the non‐breeding period. We documented cavity use throughout the annual cycle of a woodpecker using light‐level geolocators. Northern Flickers Colaptes auratus spent 63–90% of nights roosting in a cavity throughout the year, including during migration. The high frequency of year‐round cavity use by Flickers suggests that cavities provide benefits beyond nest‐sites. Our work highlights the potential use of geolocators to examine cavity use.     

When an epithelium ceases to exist – an ultrastructural study on the fate of the embryonic coelom in Epiperipatus biolleyi (Onychophora, Peripatidae)

It is an accepted fact that fusion between the coelomic cavities and the primary body cavity occurs during development in the Arthropoda. However, such a fusion is much disputed in the Onychophora. In order to clarify this subject, the fate of embryonic coelomic cavities has been studied in an onychophoran. Ultrastructural investigations in this paper provide evidence that embryonic coelomic cavities fuse with spaces of the primary body cavity in Epiperipatus biolleyi. During embryogenesis, the somatic and splanchnic portions of the mesoderm separate and the former coelomic linings are transformed into mesenchymatic tissue. The resulting body cavity therefore represents a mixture of primary and secondary (coelomic) body cavities, i.e. the ‘mixocoel’. The nephridial anlage is already present, when the ‘mixocoel’ is formed, although there is no trace of a sacculus yet. The lumen of the nephridial anlage, thus, communicates with the newly formed ‘mixocoel’. Accordingly, the lumen of the nephridial sacculus cannot be regarded as a kind of ‘persisting coelomic cavity’ in E. biolleyi. Our findings support the hypothesis that the ‘mixocoel’ was already present in the common stem species of the Onychophora and Euarthropoda.     

Development of head and trunk mesoderm in the dogfish,Scyliorhinus torazame: I. Embryology and morphology of the head cavities and related structures

Vertebrate head segmentation has attracted the attention of comparative and evolutionary morphologists for centuries, given its importance for understanding the developmental body plan of vertebrates and its evolutionary origin. In particular, the segmentation of the mesoderm is central to the problem. The shark embryo has provided a canonical morphological scheme of the head, with its epithelialized coelomic cavities (head cavities), which have often been regarded as head somites. To understand the evolutionary significance of the head cavities, the embryonic development of the mesoderm was investigated at the morphological and histological levels in the shark, Scyliorhinus torazame. Unlike somites and some enterocoelic mesodermal components in other vertebrates, the head cavities in S. torazame appeared as irregular cyst(s) in the originally unsegmented mesenchymal head mesoderm, and not via segmentation of an undivided coelom. The mandibular cavity appeared first in the paraxial part of the mandibular mesoderm, followed by the hyoid cavity, and the premandibular cavity was the last to form. The prechordal plate was recognized as a rhomboid roof of the preoral gut, continuous with the rostral notochord, and was divided anteroposteriorly into two parts by the growth of the hypothalamic primordium. Of those, the posterior part was likely to differentiate into the premandibular cavity, and the anterior part disappeared later. The head cavities and somites in the trunk exhibited significant differences, in terms of histological appearance and timing of differentiation. The mandibular cavity developed a rostral process secondarily; its homology to the anterior cavity reported in some elasmobranch embryos is discussed.     

Characteristics of nest cavities of Barrow's Goldeneyes in eastern Canada

ABSTRACT Barrow's Goldeneyes (Bucephala islandica) are secondary cavity nesters found in western North America and, to a lesser extent, in eastern North America. The eastern North American population is concentrated in the province of Québec and totals about 2000 pairs. Characteristics of nest cavities used by Barrow's Goldeneyes have been described in western North America, but no nest cavities have been found in eastern North America. From 2004 to 2008, we searched for nest cavities in the species’ core breeding area in the boreal forests north of the St. Lawrence River. We captured 12 adult females on their breeding grounds and fitted them with transmitters, but none apparently nested so we conducted ground searches in areas near lakes where paired birds were observed. We found 11 cavities, with 10 in dead, decaying trees and one in the dead part of a dying tree. Nine cavities were in white birch (Betula papyrifera) trees. Mean cavity height was 3.5 ± 1.6 (SD) m (range = 1.2–6.6 m) and mean diameter at breast height (DBH) of cavity trees was 37.8 ± 4.7 cm (range = 32.2–47.5 cm). In contrast to the population in western North America, Barrow's Goldeneyes in eastern North America appear to rely on the availability of natural cavities formed in large, decaying trees for nesting. Current forestry regulations in Québec do not promote the retention of either large trees or older forests, reducing the availability of potential nest cavities for Barrow's Goldeneyes and likely threatening their long‐term conservation. Therefore, we recommend that guidelines be developed to promote silvicultural practices aimed at preserving the long‐term availability of large (DBH ≥ 30 cm) decaying trees across the breeding range of Barrow's Goldeneyes.     

Density, Distribution, and Attributes of Tree Cavities in an Old-Growth Tropical Rain Forest

Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.