A cis-regulatory sequence of the selector gene vestigial drives the evolution of wing scaling in Drosophila species

Scaling between specific organs and overall body size has long fascinated biologists, being a primary mechanism by which organ shapes evolve. Yet, the genetic mechanisms that underlie the evolution of scaling relationships remain elusive. Here, we compared wing and fore tibia lengths (the latter as a proxy of body size) in Drosophila melanogaster, Drosophila simulans, Drosophila ananassae and Drosophila virilis, and show that the first three of these species have roughly a similar wing-to-tibia scaling behavior. In contrast, D. virilis exhibits much smaller wings relative to their body size compared with the other species and this is reflected in the intercept of the wing-to-tibia allometry. We then asked whether the evolution of this relationship could be explained by changes in a specific cis-regulatory region or enhancer that drives expression of the wing selector gene, vestigial (vg), whose function is broadly conserved in insects and contributes to wing size. To test this hypothesis directly, we used CRISPR/Cas9 to replace the DNA sequence of the predicted Quadrant Enhancer (vgQE) from D. virilis for the corresponding vgQE sequence in the genome of D. melanogaster. Strikingly, we discovered that D. melanogaster flies carrying the D. virilis vgQE sequence have wings that are significantly smaller with respect to controls, partially shifting the intercept of the wing-to-tibia scaling relationship towards that observed in D. virilis. We conclude that a single cis-regulatory element in D. virilis contributes to constraining wing size in this species, supporting the hypothesis that scaling could evolve through genetic variations in cis-regulatory elements.

Slit-independent guidance of longitudinal axons by Drosophila Robo3

Drosophila Robo3 is a member of the evolutionarily conserved Roundabout (Robo) receptor family and one of three Drosophila Robo paralogs. During embryonic ventral nerve cord development, Robo3 does not participate in canonical Slit-dependent midline repulsion, but instead regulates the formation of longitudinal axon pathways at specific positions along the medial-lateral axis. Longitudinal axon guidance by Robo3 is hypothesized to be Slit dependent, but this has not been directly tested. Here we create a series of Robo3 variants in which the N-terminal Ig1 domain is deleted or modified, in order to characterize the functional importance of Ig1 and Slit binding for Robo3's axon guidance activity. We show that Robo3 requires its Ig1 domain for interaction with Slit and for proper axonal localization in embryonic neurons, but deleting Ig1 from Robo3 only partially disrupts longitudinal pathway formation. Robo3 variants with modified Ig1 domains that cannot bind Slit retain proper localization and fully rescue longitudinal axon guidance. Our results indicate that Robo3 guides longitudinal axons independently of Slit, and that sequences both within and outside of Ig1 contribute to this Slit-independent activity.

Characterization of enhancer fragments in Drosophila robo2

Receptor proteins of the Roundabout (Robo) family regulate axon guidance decisions during nervous system development. Among the three Drosophila robo family genes (robo1, robo2 and robo3), robo2 displays a dynamic expression pattern and regulates multiple axon guidance outcomes, including preventing midline crossing in some axons, promoting midline crossing in others, forming lateral longitudinal axon pathways, and regulating motor axon guidance. The identity and location of enhancer elements regulating robo2's complex and dynamic expression pattern in different neural cell types are unknown. Here, we characterize a set of 17 transgenic lines expressing GAL4 under the control of DNA sequences derived from noncoding regions in and around robo2, to identify enhancers controlling specific aspects of robo2 expression in the embryonic ventral nerve cord. We identify individual fragments that confer expression in specific cell types where robo2 is known to function, including early pioneer neurons, midline glia and lateral longitudinal neurons. Our results indicate that robo2's dynamic expression pattern is specified by a combination of enhancer elements that are active in different subsets of cells. We show that robo2's expression in lateral longitudinal axons represents two genetically separable subsets of neurons, and compare their axon projections with each other and with Fasciclin II (FasII), a commonly used marker of longitudinal axon pathways. In addition, we provide a general description of each fragment's expression in embryonic tissues outside of the nervous system, to serve as a resource for other researchers interested in robo2 expression and its functional roles outside the central nervous system.

The vestigial Quadrant Enhancer is dispensable for pattern formation and development of the Drosophila wing

In Drosophila , the pattern of the wing selector gene, vestigial ( vg ), is established by at least two enhancers: the Boundary Enhancer, which drives expression along the disc's Dorsal-Ventral boundary; and the Quadrant Enhancer (QE) that patterns the rest of the wing pouch. Using CRISPR/Cas9 editing, we deleted DNA fragments around the reported QE sequence and found that the full Vg pattern is formed. Furthermore, adult wings arising from these gene-edited animals are normal in shape and pattern, but slightly smaller in size, although this reduction is not wing-specific in males. We suggest that other enhancers act redundantly to establish the vg pattern and rescue wing development.

Molecular phylogeny reveals the past transoceanic voyages of drywood termites (Isoptera, Kalotermitidae)

Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Ma (75–93 Ma 95% highest posterior density), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at <50 Ma, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae.

The Slit-binding Ig1 domain is required for multiple axon guidance activities of Drosophila Robo2

Drosophila Robo2 is a member of the evolutionarily conserved Roundabout (Robo) family of axon guidance receptors. Robo receptors signal midline repulsion in response to Slit ligands, which bind to the N‐terminal Ig1 domain in most family members. In the Drosophila embryonic ventral nerve cord, Robo1 and Robo2 signal Slit‐dependent midline repulsion, while Robo2 also regulates the medial‐lateral position of longitudinal axon pathways and acts non‐autonomously to promote midline crossing of commissural axons. While Robo2 signals midline repulsion in response to Slit, it is less clear whether Robo2's other activities are also Slit‐dependent. To determine which of Robo2's axon guidance roles depend on its Slit‐binding Ig1 domain, we used a clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9‐based strategy to replace the endogenous robo2 gene with a robo2 variant lacking the Ig1 domain (robo2∆Ig1). We compare the expression and localization of Robo2∆Ig1 protein with full‐length Robo2 in embryonic neurons in vivo and examine its ability to substitute for Robo2 to mediate midline repulsion and lateral axon pathway formation. We find that the removal of the Ig1 domain from Robo2∆Ig1 disrupts both of these axon guidance activities. In addition, we find that the Ig1 domain of Robo2 is required for its proper subcellular localization in embryonic neurons, a role that is not shared by the Ig1 domain of Robo1. Finally, we report that although FasII‐positive lateral axons are misguided in embryos expressing Robo2∆Ig1, the axons that normally express Robo2 are correctly guided to the lateral zone, suggesting that Robo2 may guide lateral longitudinal axons through a cell non‐autonomous mechanism.

Conserved and divergent aspects of Robo receptor signaling and regulation between Drosophila Robo1 and C. elegans SAX-3

The evolutionarily conserved Roundabout (Robo) family of axon guidance receptors control midline crossing of axons in response to the midline repellant ligand Slit in bilaterian animals including insects, nematodes, and vertebrates. Despite this strong evolutionary conservation, it is unclear whether the signaling mechanism(s) downstream of Robo receptors are similarly conserved. To directly compare midline repulsive signaling in Robo family members from different species, here we use a transgenic approach to express the Robo family receptor SAX-3 from the nematode Caenorhabditis elegans in neurons of the fruit fly, Drosophila melanogaster. We examine SAX-3's ability to repel Drosophila axons from the Slit-expressing midline in gain of function assays, and test SAX-3's ability to substitute for Drosophila Robo1 during fly embryonic development in genetic rescue experiments. We show that C. elegans SAX-3 is properly translated and localized to neuronal axons when expressed in the Drosophila embryonic CNS, and that SAX-3 can signal midline repulsion in Drosophila embryonic neurons, although not as efficiently as Drosophila Robo1. Using a series of Robo1/SAX-3 chimeras, we show that the SAX-3 cytoplasmic domain can signal midline repulsion to the same extent as Robo1 when combined with the Robo1 ectodomain. We show that SAX-3 is not subject to endosomal sorting by the negative regulator Commissureless (Comm) in Drosophila neurons in vivo, and that peri-membrane and ectodomain sequences are both required for Comm sorting of Drosophila Robo1.

Minimal structural elements required for midline repulsive signaling and regulation of Drosophila Robo1

The Roundabout (Robo) family of axon guidance receptors has a conserved ectodomain arrangement of five immunoglobulin-like (Ig) domains plus three fibronectin type III (Fn) repeats. Based on the strong evolutionary conservation of this domain structure among Robo receptors, as well as in vitro structural and domain-domain interaction studies of Robo family members, this ectodomain arrangement is predicted to be important for Robo receptor signaling in response to Slit ligands. Here, we define the minimal ectodomain structure required for Slit binding and midline repulsive signaling in vivo by Drosophila Robo1. We find that the majority of the Robo1 ectodomain is dispensable for both Slit binding and repulsive signaling. We show that a significant level of midline repulsive signaling activity is retained when all Robo1 ectodomain elements apart from Ig1 are deleted, and that the combination of Ig1 plus one additional ectodomain element (Ig2, Ig5, or Fn3) is sufficient to restore midline repulsion to wild type levels. Further, we find that deleting four out of five Robo1 Ig domains (ΔIg2-5) does not affect negative regulation of Robo1 by Commissureless (Comm) or Robo2, while variants lacking all three fibronectin repeats (ΔFn1-3 and ΔIg2-Fn3) are insensitive to regulation by both Comm and Robo2, signifying a novel regulatory role for Robo1's Fn repeats. Our results provide an in vivo perspective on the importance of the conserved 5+3 ectodomain structure of Robo receptors, and suggest that specific biochemical properties and/or ectodomain structural conformations observed in vitro for domains other than Ig1 may have limited significance for in vivo signaling in the context of midline repulsion.

Decreased mRNA and protein stability of W1282X limits response to modulator therapy

BACKGROUND

Cell-based studies have shown that W1282X generates a truncated protein that can be functionally augmented by modulators. However, modulator treatment of primary cells from individuals who carry two copies of W1282X generates no functional CFTR. To understand the lack of response to modulators, we investigated the effect of W1282X on CFTR RNA transcript levels.

METHODS

qRT-PCR and RNA-seq were performed on primary nasal epithelial (NE) cells of a previously studied individual who is homozygous for W1282X, her carrier parents and control individuals without nonsense variants in CFTR.

RESULTS

CFTR RNA bearing W1282X in NE cells shows a steady-state level of 4.2 ± 0.9% of wild-type (WT) CFTR RNA in the mother and 12.4 ± 1.3% in the father. NMDI14, an inhibitor of nonsense-mediated mRNA decay (NMD), restored W1282X mRNA to almost 50% of WT levels in the parental NE cells. RNA-seq of the NE cells homozygous for W1282X showed that CFTR transcript level was reduced to 1.7% of WT (p-value: 4.6e-3). Negligible truncated CFTR protein was generated by Flp-In 293 cells stably expressing the W1282X EMG even though CFTR transcript was well above levels observed in the parents and proband. Finally, we demonstrated that NMD inhibition improved the stability and response to correctors of W1282X-CFTR protein expressed in the Flp-In-293 cells.

CONCLUSION

These results show that W1282X can cause substantial degradation of CFTR mRNA that has to be addressed before efforts aimed at augmenting CFTR protein function can be effective.

In Vivo Functional Analysis of Drosophila Robo1 Fibronectin Type-III Repeats

The repellant ligand Slit and its Roundabout (Robo) family receptors regulate midline crossing of axons during development of the embryonic central nervous system (CNS). Slit proteins are produced at the midline and signal through Robo receptors to repel axons from the midline. Disruption of Slit-Robo signaling causes ectopic midline-crossing phenotypes in the CNS of a broad range of animals, including insects and vertebrates. While previous studies have investigated the roles of Drosophila melanogaster Robo1's five Immunoglobulin-like (Ig) domains, little is known about the importance of the three evolutionarily conserved Fibronectin (Fn) type-III repeats. We have individually deleted each of Drosophila Robo1's three Fn repeats, and then tested these Robo1 variants in vitro to determine their ability to bind Slit in cultured Drosophila cells and in vivo to investigate the requirement for each domain in regulating Robo1's embryonic expression pattern, axonal localization, midline repulsive function, and sensitivity to Commissureless (Comm) downregulation. We demonstrate that the Fn repeats are not required for Robo1 to bind Slit or for proper expression of Robo1 in Drosophila embryonic neurons. When expressed in a robo1 mutant background, these variants are able to restore midline repulsion to an extent equivalent to full-length Robo1. We identify a novel requirement for Fn3 in the exclusion of Robo1 from commissures and downregulation of Robo1 by Comm. Our results indicate that each of the Drosophila Robo1 Fn repeats are individually dispensable for the protein's role in midline repulsion, despite the evolutionarily conserved "5 + 3" protein structure.

Evaluation of fipronil and imidacloprid as bait active ingredients against fungus-growing termites (Blattodea: Termitidae: Macrotermitinae)

Fungus-growing termites (Macrotermitinae) are important pests in tropical countries. They are difficult to control with existing baiting methods, as chitin synthesis inhibitors are not effectual as active ingredients. We tested two neurotoxins, fipronil and imidacloprid, as potential bait active ingredients against Macrotermes gilvus (Hagen) in Singapore. In laboratory bioassays, M. gilvus showed no preference for doses of 0-64 ppm fipronil, or for doses of 0-250 ppm imidacloprid, indicating no repellence. We tested each insecticide in toilet paper as a bait matrix in a field experiment. After 28 days, termites had eaten 5-13% of the fipronil treated toilet paper, abandoned bait and monitoring stations, contacted no new stations, and repaired poorly their experimentally damaged mounds. Termites ate no imidacloprid treated toilet paper, abandoned bait stations although contacted new stations, and repaired fully their damaged mounds. Termites ate 60-70% of the control toilet paper, remained in bait stations, and fully repaired damaged mounds. After 56 days, all five fipronil colonies were eliminated, whereas all of the imidacloprid and control colonies were healthy. The results suggest that fipronil could be an effective active ingredient in bait systems for fungus-growing termites in tropical countries.

Midline axon guidance in the Drosophila embryonic central nervous system

Studies in the fruit fly Drosophila melanogaster have provided many fundamental insights into the genetic regulation of neural development, including the identification and characterization of evolutionarily conserved axon guidance pathways and their roles in important guidance decisions. Due to its highly organized and fast-developing embryonic nervous system, relatively small number of neurons, and molecular and genetic tools for identifying, labeling, and manipulating individual neurons or small neuronal subsets, studies of axon guidance in the Drosophila embryonic CNS have allowed researchers to dissect these genetic mechanisms with a high degree of precision. In this review, we discuss the major axon guidance pathways that regulate midline crossing of axons and the formation and guidance of longitudinal axon tracts, two processes that contribute to the development of the precise three-dimensional structure of the insect nerve cord. We focus particularly on recent insights into the roles and regulation of canonical midline axon guidance pathways, and on additional factors and pathways that have recently been shown to contribute to axon guidance decisions at and near the midline.

CRISPR-based gene replacement reveals evolutionarily conserved axon guidance functions of Drosophila Robo3 and Tribolium Robo2/3

Background

Axon guidance receptors of the Roundabout (Robo) family regulate a number of axon guidance outcomes in bilaterian animals in addition to their canonical role in Slit-dependent midline repulsion. In the fruit fly Drosophila melanogaster, three Robo paralogs (Robo1, Robo2, and Robo3) each have specialized roles in regulating midline crossing and the formation of longitudinal axon pathways in the embryonic ventral nerve cord. The number of robo genes differs in other insects, and it is unknown whether the roles and/or signaling mechanisms of Drosophila Robos are shared in other insect species. To directly compare the axon guidance activities of Robo receptors in Drosophila and the flour beetle Tribolium castaneum, I have used a CRISPR/Cas9-based approach to replace Drosophila robo3 with Tribolium robo2/3.

Results

I show that when expressed from the robo3 locus in Drosophila embryos, Tribolium Robo2/3 (TcRobo2/3) protein is properly translated and localized to axons, where it reproduces the normal expression pattern of Drosophila Robo3. In embryos expressing TcRobo2/3 in place of robo3, two distinct subsets of longitudinal axons are guided properly to their normal positions in the intermediate neuropile, indicating that TcRobo2/3 can promote Robo3-dependent axon guidance decisions in developing Drosophila neurons.

Conclusions

These observations suggest that the mechanism by which Drosophila Robo3 promotes longitudinal pathway formation is evolutionarily conserved in Tribolium, where it is performed by TcRobo2/3. The CRISPR/Cas9-based gene replacement approach described here can be applied to comparative evolutionary developmental studies of other Drosophila genes and their orthologs in other species.

Embryonic axon guidance: insights from Drosophila and other insects

During embryonic development, growing axons are guided by cellular signaling pathways that control a series of individual axon guidance decisions. In Drosophila, two major pathways (Netrin-Frazzled/DCC and Slit-Robo) regulate axon guidance in the embryonic ventral nerve cord, including the critical decision of whether or not to cross the midline. Studies in the fruit fly have revealed a complex picture of precise regulation and cross-talk between these pathways. In addition, Robo receptors in Drosophila have diversified their activities to regulate additional axon guidance decisions in the developing embryo. Here, I discuss recent advances in understanding roles and regulation of the Net-Fra and Slit-Robo signaling pathways in Drosophila, and examine the evolutionary conservation of these signaling mechanisms across insects and other arthropods.

Genotyping-by-Sequencing to Predict Resistance to Lima Bean Downy Mildew in a Diversity Panel

Lima bean is affected by severe downy mildew epidemics caused by the oomycete Phytophthora phaseoli. There are six documented races of P. phaseoli (A to F). Race F is currently predominant in the mid-Atlantic region, creating the need for resistant lima bean cultivars with desirable agronomic characteristics. In order to develop markers for detecting race F resistance, bulked segregant analysis (BSA) using genotyping-by-sequencing (GBS) was used on a biparental F₂ population comprised of 216 lima bean progeny segregating for a dominant race F resistance phenotype. Data were analyzed using a custom bioinformatic analysis pipeline (redrep). Kompetitive allele-specific polymerase chain reaction assays were developed using 12 GBS markers associated with the race F resistance phenotype. Using these assays, the F₂ population was used to map the race F resistance locus. Seven markers were in linkage and significantly associated with race F resistance that mapped between two markers located approximately 4.88 centimorgan (cM) apart. These assays were successfully used to genotype a newly acquired lima bean diversity panel consisting of 256 landraces, cultivars, and wild germplasm, and a haplotype consisting of two of the seven linked markers was demonstrated to accurately predict race F resistance. This confirmed the ability of our customized methods to accurately predict phenotypes in diverse lines of lima bean.

In vivo functional analysis of Drosophila Robo1 immunoglobulin-like domains

BACKGROUND

In animals with bilateral symmetry, midline crossing of axons in the developing central nervous system is regulated by Slit ligands and their neuronal Roundabout (Robo) receptors. Multiple structural domains are present in an evolutionarily conserved arrangement in Robo family proteins, but our understanding of the functional importance of individual domains for midline repulsive signaling is limited.

METHODS

We have examined the functional importance of each of the five conserved immunoglobulin-like (Ig) domains within the Drosophila Robo1 receptor. We generated a series of Robo1 variants, each lacking one of the five Ig domains (Ig1-5), and tested each for their ability to bind Slit when expressed in cultured Drosophila cells. We used a transgenic approach to express each variant in robo1's normal expression pattern in wild-type and robo1 mutant embryos, and examined the effects of deleting each domain on receptor expression, axonal localization, regulation, and midline repulsive signaling in vivo.

RESULTS

We show that individual deletion of Ig domains 2-5 does not interfere with Robo1's ability to bind Slit, while deletion of Ig1 strongly disrupts Slit binding. None of the five Ig domains (Ig1-5) are individually required for proper expression of Robo1 in embryonic neurons, for exclusion from commissural axon segments in wild-type embryos, or for downregulation by Commissureless (Comm), a negative regulator of Slit-Robo repulsion in Drosophila. Each of the Robo1 Ig deletion variants (with the exception of Robo1∆Ig1) were able to restore midline crossing in robo1 mutant embryos to nearly the same extent as full-length Robo1, indicating that Ig domains 2-5 are individually dispensable for midline repulsive signaling in vivo.

CONCLUSIONS

Our findings indicate that four of the five Ig domains within Drosophila Robo1 are dispensable for its role in midline repulsion, despite their strong evolutionary conservation, and highlight a unique requirement for the Slit-binding Ig1 domain in the regulation of midline crossing.

Slit Binding via the Ig1 Domain Is Essential for Midline Repulsion by Drosophila Robo1 but Dispensable for Receptor Expression, Localization, and Regulation in Vivo

The midline repellant ligand Slit and its Roundabout (Robo) family receptors constitute the major midline repulsive pathway in bilaterians. Slit proteins produced at the midline of the central nervous system (CNS) signal through Robo receptors expressed on axons to prevent them from crossing the midline, and thus regulate connectivity between the two sides of the nervous system. Biochemical structure and interaction studies support a model in which Slit binding to the first immunoglobulin-like (Ig1) domain of Robo receptors activates a repulsive signaling pathway in axonal growth cones. Here, we examine the in vivo functional importance of the Ig1 domain of the Drosophila Robo1 receptor, which controls midline crossing of axons in response to Slit during development of the embryonic CNS. We show that deleting Ig1 from Robo1 disrupts Slit binding in cultured Drosophila cells, and that a Robo1 variant lacking Ig1 (Robo1(∆Ig1)) is unable to promote ectopic midline repulsion in gain-of-function studies in the Drosophila embryonic CNS. We show that the Ig1 domain is not required for proper expression, axonal localization, or Commissureless (Comm)-dependent regulation of Robo1 in vivo, and we use a genetic rescue assay to show that Robo1(∆Ig1) is unable to substitute for full-length Robo1 to properly regulate midline crossing of axons. These results establish a direct link between in vitro biochemical studies of Slit-Robo interactions and in vivo genetic studies of Slit-Robo signaling during midline axon guidance, and distinguish Slit-dependent from Slit-independent aspects of Robo1 expression, regulation, and activity during embryonic development.

Robo2 acts in trans to inhibit Slit-Robo1 repulsion in pre-crossing commissural axons

During nervous system development, commissural axons cross the midline despite the presence of repellant ligands. In Drosophila, commissural axons avoid premature responsiveness to the midline repellant Slit by expressing the endosomal sorting receptor Commissureless, which reduces surface expression of the Slit receptor Roundabout1 (Robo1). In this study, we describe a distinct mechanism to inhibit Robo1 repulsion and promote midline crossing, in which Roundabout2 (Robo2) binds to and prevents Robo1 signaling. Unexpectedly, we find that Robo2 is expressed in midline cells during the early stages of commissural axon guidance, and that over-expression of Robo2 can rescue robo2-dependent midline crossing defects non-cell autonomously. We show that the extracellular domains required for binding to Robo1 are also required for Robo2's ability to promote midline crossing, in both gain-of-function and rescue assays. These findings indicate that at least two independent mechanisms to overcome Slit-Robo1 repulsion in pre-crossing commissural axons have evolved in Drosophila.

International field trials of pyrethroid-treated wood exposed to Coptotermes acinaciformis in Australia and Coptotermes formosanus (Isoptera: Rhinotermitidae) in China and the United States

Coptotermes Wasmann is one of the most important genera of wood-destroying insect pests, both in its native and introduced countries. Pyrethroids are among the most widely used insecticides in wood preservation around the world. Consequently, they have often been evaluated against different species of Coptotermes. However, because various test methods have been used between countries, comparing results is problematic. These field trials, using a single aboveground method of exposure, assessed a range of retentions of two pyrethroids (bifenthrin and permethrin) in Pinus radiata D. Don sapwood against two species of Coptotermes in three countries to provide directly comparable results. Coptotermes acinaciformis (Froggatt) in Australia consumed the most nontreated wood, followed by Coptotermes formosanus Shiraki in China, then C. formosanus in the United States, although these data were not significantly different. Both termite species demonstrated a dose-response to wood treated with the two pyrethroids; less wood was consumed as retention increased. Overall, C. acinaciformis consumed relatively little of the treated wood. In comparison, C. formosanus consumed 20-90% of the wood treated at the lowest retentions of the pyrethroids evaluated. Results indicated that C. acinaciformis was more sensitive to pyrethroid toxicity/repellency compared with C. formosanus. Factors that may have influenced the results are discussed. However, using a single aboveground method of exposure across three countries, that suited both species of Coptotermes, made it possible to determine unambiguously the actual differences between the species in their tolerances to the two pyrethroid insecticides.

Delaying gratification for food and tokens in capuchin monkeys (Cebus apella) and chimpanzees (Pan troglodytes): when quantity is salient, symbolic stimuli do not improve performance

Capuchin monkeys have been tested for the capacity to delay gratification for accumulating rewards in recent studies and have exhibited variable results. Meanwhile, chimpanzees have consistently excelled at this task. However, neither species have ever been tested at accumulating symbolic tokens instead of food items, even though previous reports indicate that tokens sometimes facilitate performance in other self-control tasks. Thus, in the present study, we tested capuchin monkeys and chimpanzees for their capacity to delay gratification in a delay maintenance task, in which an experimenter presented items, one at a time, to within reach of an animal for as long as the animal refrained from taking them. In Experiment 1, we assessed how long capuchin monkeys could accumulate items in the delay maintenance task when items were food rewards or tokens exchangeable for food rewards. Monkeys accumulated more food rewards than they did tokens. In Experiment 2, we tested capuchin monkeys and chimpanzees in a similar accumulation test. Whereas capuchins again accumulated more food than tokens, all chimpanzees but one showed no difference in performance in the two conditions. These findings provide additional evidence that chimpanzees exhibit greater self-control capacity in this task than do capuchin monkeys and indicate that symbolic stimuli fail to facilitate delay maintenance when they do not abstract away from the quantitative dimension of the task. This is consistent with previous findings on the effects of symbols on self-control and illuminates what makes accumulation a particularly challenging task.

Slit/Robo-mediated axon guidance in Tribolium and Drosophila: divergent genetic programs build insect nervous systems

As the complexity of animal nervous systems has increased during evolution, developmental control of neuronal connectivity has become increasingly refined. How has functional diversification within related axon guidance molecules contributed to the evolution of nervous systems? To address this question, we explore the evolution of functional diversity within the Roundabout (Robo) family of axon guidance receptors. In Drosophila, Robo and Robo2 promote midline repulsion, while Robo2 and Robo3 specify the position of longitudinal axon pathways. The Robo family has expanded by gene duplication in insects; robo2 and robo3 exist as distinct genes only within dipterans, while other insects, like the flour beetle Tribolium castaneum, retain an ancestral robo2/3 gene. Both Robos from Tribolium can mediate midline repulsion in Drosophila, but unlike the fly Robos cannot be down-regulated by Commissureless. The overall architecture and arrangement of longitudinal pathways are remarkably conserved in Tribolium, despite it having only two Robos. Loss of TcSlit causes midline collapse of axons in the beetle, a phenotype recapitulated by simultaneous knockdown of both Robos. Single gene knockdowns reveal that beetle Robos have specialized axon guidance functions: TcRobo is dedicated to midline repulsion, while TcRobo2/3 also regulates longitudinal pathway formation. TcRobo2/3 knockdown reproduces aspects of both Drosophila robo2 and robo3 mutants, suggesting that TcRobo2/3 has two functions that in Drosophila are divided between Robo2 and Robo3. The ability of Tribolium to organize longitudinal axons into three discrete medial-lateral zones with only two Robo receptors demonstrates that beetle and fly achieve equivalent developmental outcomes using divergent genetic programs.

First Report of Downy Mildew of Lima Bean Caused by Phytophthora phaseoli in Virginia

Delaware, the eastern shore of Maryland, and southern New Jersey have been the center of lima bean (Phaseolus lunatus L.) production in the eastern United States for nearly 50 years (1). Downy mildew has been the most important disease of lima bean in the humid eastern United States over that period. The causal agent of downy mildew, the oomycete pathogen Phytophthora phaseoli Thaxt., was first identified on lima bean in Connecticut in 1887 by Thaxter. Signs and symptoms of lima bean downy mildew include infection, necrosis and abscission of flowers, and shepherd's crooking of racemes, shoot tips, and petioles (1). Sporangia develop on shoot tips, petioles, pins (small pods), and pods in the field and on hypocotyls in-vitro. Since 2005, approximately 50% of the baby lima beans processed in the United States have been grown in Delaware and the eastern shore of Maryland. In 2008, commercial lima bean production began on the eastern shore of Virginia in Accomack County but no downy mildew was reported in that season. In 2009, approximately 1,825 ha in Accomack and Northampton counties were planted to baby lima bean. Weather conditions in 2009, including above average rainfall, were conducive for the development of downy mildew on the Delmarva Peninsula. Downy mildew was widespread in growers' fields in August and September in butter bean in southern New Jersey and baby lima bean in Sussex County, DE. In August 2009, a home gardener in Rappahannock, VA sent samples of infected lima bean pods from baby, Fordhook, and pole lima bean plants to the Virginia Tech Plant Disease Clinic in Blacksburg. On the basis of morphometric analysis, samples were determined microscopically to be infected by a Phytophthora sp. with rather uniform sporangia averaging 39 × 22 μm and short pedicels, diagnostic for P. phaseoli (1). On October 27, 2009, field scouts in Accomack County, VA identified two lima bean fields planted to cv. C-Elite-Select exhibiting moderate symptoms of downy mildew. Samples were brought to the Plant Diagnostic Clinic at the University of Delaware under USDA-APHIS permit and determined to be P. phaseoli based on morphometric analysis. Samples were inoculated onto a lima bean cultivar differential to determine pathogenicity to complete Koch's postulates and to determine their physiological race. Samples were inoculated onto lima bean cvs. 184-185 and C-Elite-Select, which are susceptible to race F and resistant to race E, Eastland and 8-78, which are susceptible to race E and resistant to race F, and Concentrated Fordhook, susceptible to all known races (1). Three pots containing five emerging seedlings each were inoculated with sporangia (approximately 10³ per ml) prepared by soaking infected pods in 500 ml of sterile distilled water for 1 min with gentle agitation. Plants were placed in a Percival dew chamber with intermittent misting and set at 19. Infection and disease development were assessed daily and signs developed 7 days postinoculation in cvs. 184-85, C-Elite-Select, and Concentrated Fordhook, but not in Eastland and 8-78. Cultivar differential tests indicated that the isolates were P. phaseoli race F. Hypocotyls of infected plants were scraped, and isolations made on lima bean pod agar confirmed the presence of P. phaseoli. To our knowledge, this is the first time that downy mildew of lima bean has been reported in Virginia. Reference: (1) T.A. Evans et al. Plant Dis. 91:128, 2007.

Functional diversity of Robo receptor immunoglobulin domains promotes distinct axon guidance decisions

Recognition molecules of the immunoglobulin (Ig) superfamily control axon guidance in the developing nervous system. Ig-like domains are among the most widely represented protein domains in the human genome, and the number of Ig superfamily proteins is strongly correlated with cellular complexity. In Drosophila, three Roundabout (Robo) Ig superfamily receptors respond to their common Slit ligand to regulate axon guidance at the midline: Robo and Robo2 mediate midline repulsion, Robo2 and Robo3 control longitudinal pathway selection, and Robo2 can promote midline crossing. How these closely related receptors mediate distinct guidance functions is not understood. We report that the differential functions of Robo2 and Robo3 are specified by their ectodomains and do not reflect differences in cytoplasmic signaling. Functional modularity of Robo2's ectodomain facilitates multiple guidance decisions: Ig1 and Ig3 of Robo2 confer lateral positioning activity, whereas Ig2 confers promidline crossing activity. Robo2's distinct functions are not dependent on greater Slit affinity but are instead due in part to differences in multimerization and receptor-ligand stoichiometry conferred by Robo2's Ig domains. Together, our findings suggest that diverse responses to the Slit guidance cue are imparted by intrinsic structural differences encoded in the extracellular Ig domains of the Robo receptors.

Effect of vibratory soldier alarm signals on the foraging behavior of subterranean termites (Isoptera: Rhinotermitidae)

Termite soldiers produce a vibratory alarm signal to warn conspecific workers. This study recorded and characterized the alarm signals of Coptotermes acinaciformis (Froggatt) (Isoptera: Rhinotermitidae) and then investigated the effect of playing these recorded alarm signals on C. acinaciformis feeding activity. Foraging groups of termites were offered paired wooden blocks: either one block, continuously stimulated with a vibratory alarm signal, paired with a nonstimulated block (the alarm treatment), continuously stimulated with a pink noise signal, paired with a nonstimulated block (control for nonspecific vibrations) or two nonstimulated blocks (control for environmental effects), for 4 wk. The amount of wood eaten in the blocks stimulated by the alarm signals was significantly less than the paired nonstimulated blocks, while there seemed to be no preference in the case of the pink noise playback or control for direction. Importantly, the termites seemed not to have adapted to the recorded alarm signal over the 4-wk duration of the experiment, unlike previous studies using nonbiologically derived signals.

Kekkon5 is an extracellular regulator of BMP signaling

Precise spatial and temporal control of Drosophila Bone Morphogenetic Protein (BMP) signaling is achieved by a host of extracellular factors that modulate ligand distribution and activity. Here we describe Kekkon5 (Kek5), a transmembrane protein containing leucine-rich repeats (LRRs), as a novel regulator of BMP signaling in Drosophila. We find that loss or gain of kek5 disrupts crossvein development and alters the early profile of phosphorylated Mad and dSRF in presumptive crossvein cells. kek5 phenotypic effects closely mimic those observed with Short gastrulation (Sog), but do not completely recapitulate the effects of dominant negative BMP receptors. We further demonstrate that Kek5 is able to antagonize the BMP ligand Glass bottom boat (Gbb) and that the Kek5 LRRs are required for BMP inhibitory activity, while the Ig domain is dispensable in this context. Our identification of Kek5 as a modulator of BMP signaling supports the emerging notion that LIG proteins function as diverse regulators of cellular communication.

Lima Bean Downy Mildew Epiphytotics Caused by New Physiological Races of Phytophthora phaseoli

Before 1995, race D of Phytophthora phaseoli, the causal agent of downy mildew on lima bean (Phaseolus lunatus), was the prevalent physiological race in the mid-Atlantic region of the United States. Since 1995, however, new physiological races of P. phaseoli have been responsible for downy mildew outbreaks in previously resistant cultivars in this region. Cultivar differential testing of 180 isolates of P. phaseoli collected between 1994 and 2005 from Delaware and the eastern shore of Maryland has confirmed the presence of two new physiological races. The detection of race E in 1995 and race F only 5 years later in 2000, plus the lack of resistant cultivars to manage the epiphytotics in lima bean, have led to millions of dollars of crop losses. Intra- and interspecific genetic variation of Phytophthora spp. and isolates were assessed using amplified fragment length polymorphism DNA fingerprinting. Primer groups EcoRI+AG and MseI+C distinguished P. phaseoli and P. capsici from P. infestans but did not distinguish among different races of P. phaseoli.

First Report of Mefenoxam-Resistant Isolates of Phytophthora capsici from Lima Bean Pods in the Mid-Atlantic Region

Phytophthora capsici Leonian, the causal agent of lima bean pod rot, was first identified as a pathogen of lima bean in 2002 (1) and poses a new threat to lima bean (Phaseolus lunatus L.) production in the Mid-Atlantic Region. The phenylamide fungicide mefenoxam (Ridomil Gold; Syngenta Crop Protection) is widely used in the region for controlling foliar and soilborne diseases caused by Oomycetes. Isolates of P. capsici were collected from lima bean pods from production fields in Delaware, Maryland, and New Jersey from 1998 to 2004. These isolates originated from survey samples of lima bean fields for another pathogen, P. phaseoli, in 1999 and 2000 and diagnostic samples were submitted to the Plant Disease Clinic. Isolates were from lima bean, except for one from pepper (basal stem). Identification was made on the basis of morphometric characteristics. No known sensitive or insensitive isolates were included in the evaluation. Single zoospore cultures were evaluated for mefenoxam sensitivity on V8 agar plates amended with 100 ppm of mefenoxam, a previously tested concentration (2). Seven-millimeter-diameter agar plugs of each isolate were cut from the edge of actively expanding cultures of P. capsici with a cork borer and transferred to three V8 agar plates amended with mefenoxam and three unamended V8 plates. The plates were arranged in a completely randomized design and incubated at 25°C in the dark for 3 days. After incubation, colony growth was measured in millimeters and averaged for the three replicate plates of each isolate and percent growth relative to the unamended control was calculated. Mefenoxam sensitivity was assigned according to methods of Lamour et al. (2). The experiment was repeated once, and also run with a treatment of 200 ppm of mefenoxam. Of sixteen isolates screened, nine were rated as sensitive, four were intermediately resistant, and three were resistant. There was no difference between the 100 and 200 ppm results, except for a slight increase in sensitivity for one isolate. A subsequent experiment tested five isolates at concentrations of 1, 10, 100, and 1,000 ppm. Results were consistent with previous tests, with resistant isolates exhibiting some growth at the highest concentration of mefenoxam. One resistant isolate was from a field in Delaware previously cropped to slicing cucumbers with a history of mefenoxam applications. The second was from Caroline County, MD, which is heavily cropped to pickling cucumbers and likely to have been exposed to mefanoxam applications for the control of fruit rot; the origin of the third insensitive isolate from lima bean is unknown. Mefanoxam usage on lima bean is usually limited to one foliar application of mefenoxam+copper hydroxide to control downy mildew in the fall crop in wet seasons. This study indicates that mefenoxam resistance is present in populations of P. capsici in lima bean fields in the Mid-Atlantic Region, presumably as a result of mefenoxam applications to other vegetable crops, principally cucurbits, which are planted in rotation with lima beans or from nearby cucurbit fields. Implementing strategies to minimize fungicide resistance in other vegetables is important to slow resistance development associated with this emerging pathogen on lima beans. Lima bean pod rot continues to be seen sporadically each year in fields with a history of P. capsici and abundant rainfall or excessive irrigation. References: (1) C. R. Davidson et al. Plant Dis. 86:1049, 2002. (2) K. H. Lamour et al. Phytopathology 90:396, 2000.

Management of Xiphinema americanum and Soybean Severe Stunt in Soybean Using Crop Rotation

Soybean severe stunt (SSS), caused by the Soybean severe stunt virus (SSSV), is a soilborne virus disease affecting soybean (Glycine max) first described in Delaware in 1988. Lack of breeding programs directed at incorporating resistance to SSSV in new cultivar releases necessitated alternative methods of SSS control. The effect of crops in 2-year rotations on the dagger nematode (Xiphinema americanum), the putative nematode vector of SSSV, and SSS severity were examined. Two years of continuous corn or grain sorghum, wheat followed by 'HT-5203' soybean, or 2-year fallow, reduced both dagger nematode density in the soil and SSS severity. Crop rotation to the SSSV-tolerant HT-5203 soybean as a single crop for 2 years increased dagger ematode populations and SSS severity. Greenhouse studies indicated that corn, wheat, marigold, castor, and fallow treatments reduced dagger nematodes the most after 14 weeks compared with 'Essex' and HT 5203 soybean.

Argos Mutants Define an Affinity Threshold for Spitz Inhibition in Vivo

Argos, a secreted antagonist of Drosophila epidermal growth factor receptor (dEGFR) signaling, acts by sequestering the activating ligand Spitz. To understand how different domains in Argos contribute to efficient Spitz sequestration, we performed a genetic screen aimed at uncovering modifiers of an Argos misexpression phenotype in the developing eye. We identified a series of suppressors mapping to the Argos transgene that affect its activity in multiple developmental contexts. These point mutations map to both the N- and C-terminal cysteine-rich regions, implicating both domains in Argos function. We show by surface plasmon resonance that these Argos mutants are deficient in their ability to bind Spitz in vitro. Our data indicate that a mere approximately 2-fold decrease in K(D) is sufficient to compromise Argos activity in vivo. This effect could be recapitulated in a cell-based assay, where a higher molar concentration of mutant Argos was needed to inhibit Spitz-dependent dEGFR phosphorylation. In contrast, a approximately 37-fold decrease in the binding constant nearly abolishes Argos activity in vivo and in cellular assays. In agreement with previously reported computational studies, our results define an affinity threshold for optimal Argos inhibition of dEGFR signaling during development.

The effect of bait design on bait consumption in termites (Isoptera: Rhinotermitidae)

The efficacy of baiting as a pest control method relies on the bait appealing to the pest species. In the case of wood-eating termites, bait stations should be designed to encourage termite presence and to maximize their consumption of bait matrix in order to expedite control in minimal time. A field experiment examined the effect of bait size (one large bait or four small baits of equivalent total size, with commensurate inspection and replacement schedules), compaction (tightly rolled or loosely folded) and composition (paper only or paper plus wood) on termite presence and on untreated bait paper removal rates over four months. All three factors were significant, with bait size the most important factor, followed by compaction and then composition. The least effective baits were small, compacted (rolled) paper-only baits with monthly inspections; these had the highest abandonment rate (70%) and had the least paper removed (mean of 24 g). The most effective baits were large, folded paper-plus-wood baits with inspections at two months; these had the lowest abandonment rate (20%) and had the highest paper removal (mean of 112 g). The more than four-fold difference between these baits types demonstrates that bait efficacy can be altered considerably merely by changing bait design without adding new ingredients to the bait matrix.

Comparative analysis of the Kekkon molecules, related members of the LIG superfamily

Leucine-rich repeats (LRRs) and immunoglobulin (Ig) domains represent two of the most abundant sequence elements in metazoan proteomes. Despite this prevalence, comparatively few molecules containing both LRR and Ig (LIG) modules exist, and fewer still have been functionally defined. One LIG whose function has been investigated is the Drosophila protein Kekkon1 (Kek1). In vivo studies have demonstrated a role for Kek1 in Epidermal Growth Factor Receptor (EGFR) signaling and have suggested a role in neuronal pathfinding. Kek1 is the founding member of the Kek family, a group of six Drosophila transmembrane proteins that contain seven LRRs and a single Ig in their extracellular domains. While this arrangement of domains predicts a possible role as cell adhesion molecules (CAMs), to date little is known about the function or evolutionary relationship of these additional Kek molecules. Here we report that orthologs of Kek1, Kek2, Kek5, and Kek6 exist in the mosquito, Anopheles gambiae, and the honeybee, Apis mellifera, indicating that this family has been conserved for ~300 million years of evolutionary time. Comparative sequence analyses reveal remarkable identity among these orthologs, primarily in their extracellular regions. In contrast, the intracellular regions are more divergent, exhibiting only small pockets of conservation. In addition, we provide support for the general notion that these molecules may share common functions as CAMs, by demonstrating that Kek family members can form homotypic and heterotypic complexes.

Effect of an Acute Bout of Soccer Heading on Postural Control and Self-Reported Concussion Symptoms

Our purpose was to determine if an acute bout of heading soccer balls adversely affected postural control and self-reported symptoms of cerebral concussion. Thirty-one college-aged soccer players were randomly placed into either a kicking group or a heading group. Subjects either kicked or headed 18 soccer balls over the course of 40 minutes. Subjects had their postural control assessed while standing on a force plate and completed a concussion symptoms checklist on three separate occasions: prior to, immediately following, and 24 hours after kicking or heading. There were no significant differences between the heading and kicking groups on the postural control measures prior to, immediately following, and 24 hours after kicking/heading. The heading group did, however, report significantly more concussion symptoms than the kicking group immediately after heading, but not 24 hours after heading. The number of previous concussions sustained by subjects did not influence the effects of heading. An acute bout of soccer heading appears to cause an increase in self-reported symptoms of cerebral concussion lasting less than 24 hours but no quantifiable deficits in postural control. Further research is needed to investigate the cumulative effects of soccer heading on postural control and other objective measures of brain function.

Comparing mark-recapture and constant removal protocols for estimating forager population size of the subterranean termite Coptotermes lacteus (Isoptera: Rhinotermitidae)

Forager population sizes of colonies of Coptotermes lacteus(Froggatt) in New South Wales were estimated using two methods: mark-recapture and constant removal, in two disturbed habitats: a pine plantation and cleared farmland. Mark-recapture population estimates were unrealistic and unreliable: they could be improbably large, over 200 million foragers, and they varied enormously between samples for each colony without any pattern. The constant removal population estimates could also be unrealistic: they could be negative or quite different when calculated using regression and maximum likelihood methods. However, the unrealistic results could be predicted reliably, and explained by the lack of re-contact with the sampling devices (bait stations) - a violation of an assumption of the method. This happened more frequently in the plantation than in the farmland, probably because of the greater abundance of alternative food sources in the plantation. Of the two methods, constant removal provided reasonable forager population estimates, relative to direct counts, at least some of the time, plus a mechanism by which reliability could be tested, whereas mark-recapture provided neither. Further refinement and testing of constant removal methods are urged to provide a more reliable population estimation technique for termites.

The influence of soil heterogeneity on exploratory tunnelling by the subterranean termite Coptotermes frenchi (Isoptera: Rhinotermitidae)

The exploration of sand-filled arenas by workers of an entire colony of the Australian, subterranean foraging, tree-nesting termite, Coptotermes frenchi Hill was investigated under laboratory conditions. The first experiment tested whether termite exploration of sand was influenced by the presence of gaps or objects in the sand. Gaps and objects were chosen to represent soil heterogeneity in the urban environment: gaps to represent tunnels dug by other animals, perspex strips to represent cables and pipes, and wood strips to represent roots. Termites always chose to explore gaps thoroughly before they began tunnelling in the sand. Significantly more and longer tunnels were excavated from the end of gaps at the far end of the arenas, and relatively little tunnelling occurred around and along objects. Termite density was significantly greater around and along wood compared with perspex blocks. The second experiment tested whether termite exploratory tunnelling was influenced by soil moisture. The termites tunnelled slowly in dry sand, but after discovering a patch of wet sand, increased tunnelling five-fold until it was completely explored, after which activity declined. Energy and water conservation may be behind these patterns of exploratory tunnelling as well as those seen in large field studies, but caution is urged when interpreting small scale laboratory experiments to explain large scale field data.

First Report of Phytophthora capsici Infecting Lima Bean (Phaseolus lunatus) in the Mid-Atlantic Region

Lima beans are an important crop in Delaware and the Mid-Atlantic Region. In the summer of 2000, five commercial cultivars (3-28, 184-85, C-elite Sel, Butter Bean, and Jackson Wonder) of lima bean in Delaware, Maryland, and New Jersey were observed with white, appressed mycelia on infected pods that appeared distinctly different from signs of downy mildew infection caused by Phytophthora phaseoli. Isolations were made by placing diseased pods between layers of rye media (1). A fungus that produced white mycelia with sporangia was consistently isolated. All Phytophthora isolates from the infected pods were heterothallic, grew at 35°C, had as much as 100 μm long pedicles on varying shapes of caducous sporangia with tapering base and >2 papillae, and were identified as P. capsici (2). Initially, three surface-disinfected pods from cv. Early Thorogreen plants grown in the greenhouse were floated on 20 ml of sterile water in a petri dish, and each was inoculated with a disk of P. capsici. This was repeated for nine isolates obtained from lima bean. After incubation for 7 days at room temperature, all 27 pods were infected, and P. capsici was reisolated from all the pods. A pathogenicity test was performed on the same cultivars from which the original field isolates were collected. Three seedlings and two plants with mature pods were inoculated with a sporangial suspension of each of the nine isolates and placed in a dew chamber for 5 days at 20 to 25°C and 100% relative humidity. White mycelial growth was observed on seedlings and mature pods. One inoculated plant developed brown-to-black stem lesions with white mycelia. All pods on the mature plants showed appressed, white mycelia identical to that observed in the commercial lima bean fields. P. capsici was consistently reisolated from all inoculated plants. In 2000, most infected pods in infested fields were observed low in the plant canopy or touching the soil. However, in 2001, infected pods were mostly in the lower and mid-portion of the plants observed in baby lima bean fields in Kent County, DE. References: (1) C. E. Caten and J. L. Jinks. Can. J. Bot. 46:329, 1967. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora capsici. Page 264 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996.

Two New Races of Phytophthora phaseoli from Lima Bean in Delaware

Downy mildew, incited by Phytophthora phaseoli Thaxt., is the most important disease of lima bean (Phaseolus lunatus L.) on the east coast of the United States. It has been a serious threat to commercial lima bean production in Delaware, Maryland, and New Jersey for the past 5 years. Growers have attempted to manage this disease using resistant cultivars and copper hydroxide fungicides. In August and September 1995, a new pathogenic race of P. phaseoli was isolated from infected pods of the lima bean cv. Packer in a production field near Milton, DE. Races of P. phaseoli are determined using a modification of a cultivar differential developed by Wester (3). The cv. 184-85, which is resistant to races A, B, C, and D (1), is susceptible to the new race, designated as E. In August 2000, another new pathogenic race of P. phaseoli was isolated from infected pods of cv. 184-85 near Middletown, DE. The lima bean line BG2-408, which is resistant to races A, B, C, D, and E, is susceptible to the new race, designated as F. Symptoms produced on lima bean plants infected by races E and F are similar to each other, and to those produced by all other races. All races of P. phaseoli have the same cultural characteristics on lima bean pod agar. Evaluations of in field weather station data and disease occurrence indicate that races E and F may have temperature maxima greater than 32°C, whereas race D has a maximum of less than 32°C (2). During the 2000 growing season, 118 isolates of P. phaseoli were collected from 44 production fields in Delaware and the eastern shore of Maryland, with 86% characterized as race E and 5% as race F. References: (1) C. R. Davidson et al. Biol. Cult. Tests 2001:V80. (2) R. A. Hyre and R. S. Cox. Phytopathology 43:419, 1953. (3) R. E. Wester. Phytopathology 60:1856, 1970.

Tunnel specificity and forager movement in subterranean termites (Isoptera: Rhinotermitidae and Termitidae)

The movement of foragers of two species of Australian, subterranean, mound-building termites, Coptotermes lacteus (Froggatt) (Rhinotermitidae) and Nasutitermes exitiosus (Hill) (Termitidae), was investigated in their natural habitat using artificial feeding sites along trenches dug to mimic natural forager tunnels that radiate out from the central mound-nests. Termites were dyed by self-feeding on cardboard soaked with histological fat-stains on one or two trenches and then termites were collected from other feeding sites at two and four weeks after the fat-stains were placed. At two and four weeks after marking commenced, 60-75% of marked termites were found in trenches containing the marked paper, and 2-16% were found in trenches on the opposite side of the nest. The proportion of marked termites in a sample was three to eight times greater in the trenches containing the marked paper relative to other trenches. Although difficulties with fat-stains used as markers might explain some of the observed patterns, it is evident that C. lacteus and N. exitiosus foragers do not move randomly between feeding sites in their natural habitat.

Estimating relative decline in populations of subterranean termites (Isoptera: Rhinotermitidae) due to baiting

Although mark-recapture protocols produce inaccurate population estimates of termite colonies, they might be employed to estimate a relative change in colony size. This possibility was tested using two Australian, mound-building, wood-eating, subterranean Coptotermes species. Three different toxicants delivered in baits were used to decrease (but not eliminate) colony size, and a single mark-recapture protocol was used to estimate pre- and postbaiting population sizes. For both species, the numbers of termites retrieved from bait stations varied widely, resulting in no significant differences in the numbers of termites sampled between treatments in either the pre- or postbaiting protocols. There were significantly fewer termites sampled in all treatments, controls included, in the postbaiting protocol compared with the pre-, suggesting a seasonal change in forager numbers. The comparison of population estimates shows a large decrease in toxicant treated colonies compared with little change in control colonies, which suggests that estimating the relative decline in population size using mark-recapture protocols might to be possible. However, the change in population estimate was due entirely to the significantly lower recapture rate in the control colonies relative to the toxicant treated colonies, as numbers of unmarked termites did not change between treatments. The population estimates should be treated with caution because low recapture rates produce dubious population estimates and, in some cases, postbaiting mark-recapture population estimates could be much greater than those at prebaiting, despite consumption of bait in sufficient quantities to cause population decline. A possible interaction between fat-stain markers and toxicants should be investigated if mark-recapture population estimates are used. Alternative methods of population change are advised, along with other indirect measures.

Genetic Structure of the Phytophthora infestans Population in Morocco

ABSRACT In 1996 to 1998, a late-blight survey was conducted in potato- and tomato-growing regions of Morocco. A total of 149 isolates of Phytophthora infestans were collected and analyzed for the glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) alleles, mating types, and metalaxyl sensitivities. Four genotypes were identified: MO-1 (mating type A1, Gpi 100/100, Pep 92/100), MO-2 (mating type A1, Gpi 86/100, Pep 92/100), MO-3 (mating type A2 Gpi 100/100, Pep 100/100), and MO-4 (mating type A1, Gpi 100/100, Pep 100/100). The potato isolates were MO-1 (1996 & 97), MO-3 (1998), and MO-4 (1998). The frequencies of A1 (MO-4) and A2 (MO-3) mating types in potato fields in 1998 were 26 and 74%, respectively. Potato isolates were pathogenic to both potatoes and tomatoes. The isolates collected from tomatoes in 1997 and 1998 were MO-2. Potato and tomato isolates were insensitive and sensitive to metalaxyl, respectively. The change of genotype population in 1998 was probably caused by migration of a new genotype from Europe associated with importation of potato seed. The detection of A1 and A2 mating types in the same potato field indicates the potential for sexual reproduction of P. infestans in Morocco.

Increased inducible apoptosis in CD4+ T lymphocytes during polymicrobial sepsis is mediated by Fas ligand and not endotoxin

Recent studies suggest that increased lymphocyte apoptosis (Ao) detected in peripheral blood T cells from burn patients appears to contribute to decreased lymphocyte immunoresponsiveness. However, while it is known that sepsis induces a marked depression in the splenocyte immune response (i.e. decreased interleukin-2, interferon-gamma production and proliferation) in response to the T-cell mitogen concanavalin A (Con A), it is unknown whether this depression is associated with an increase in inducible Ao and if so, which mediators control this process. To assess this, splenocytes were harvested from mice at 24 hr (a period associated with decreased Con A response) after the onset of polymicrobial sepsis [caecal ligation and puncture (CLP)] or sham-CLP (Sham) and then stimulated with 2.5 microg Con A/ml (24 hr). Septic mouse splenocytes stimulated with Con A, while not showing a change in their phenotypic make-up, did exhibit a marked increase in the percentage of splenocyte that were Ao+ which was associated with altered cytokine release. This appears to be due to an increase in the percentage of Ao+ cells in the CD4+ CD8- population and was associated with enhanced Fas antigen expression as well as an increase in mRNA for the Fas-FasL gene family. To determine if the changes in Ao are due to either endotoxin (a product of Gram-negative bacteria seen in CLP mice) or the expression of Fas ligand (FasL; a mediator of activation-induced lymphocyte Ao), a second set of studies examining Con A-inducible Ao was performed with splenocytes harvested from septic endotoxin-tolerant C3H/HeJ and the FasL-deficient C3H/HeJ-Fasl gld mice. The results show that increased splenocyte Ao detected following CLP is due to a FasL-mediated process and not to endotoxin. Thus the inadvertent up-regulation of FasL-mediated splenocyte Ao may contribute to the depression of splenocyte immune responses seen during polymicrobial sepsis.

Septic arthritis of the knee following anterior cruciate ligament reconstruction: results of a survey of sports medicine fellowship directors

To determine the incidence of joint sepsis following anterior cruciate ligament (ACL) reconstruction and the prevailing attitudes toward its treatment, we surveyed the directors of Sports Medicine Fellowship programs about their practices in treating and preventing this complication. Of the 74 surgeons surveyed, 61 (82%) responded. These 61 surgeons performed an average of 98 ACL reconstructions yearly; 31 (51 %) routinely used a drain after ACL surgery, 18 (30%) had treated an ACL infection within the past 2 years, and 26 (43%) had treated an infection within the past 5 years. There was no significant difference in the number of infections and the surgeons' case load, graft choice, or method of reconstruction. Fifty-two surgeons (85%) selected culture-specific intravenous (IV) antibiotics and surgical irrigation of the joint with graft retention as initial treatment for the infected patellar tendon autograft, and 39 (64%) chose this regimen to treat the infected allograft. For the resistant infection unresponsive to initial treatment, IV antibiotics with surgical irrigation and graft retention were also selected as the most common treatment combination for 25 (39%) of the 61 respondents. After graft removal, the earliest a revision procedure would be considered was 6 to 9 months. The results of this survey confirm the widely held belief that septic arthritis of the knee is a relatively rare complication following ACL reconstruction. Once an infection is encountered, culture-specific IV antibiotics and surgical joint irrigation with graft retention are recommended as initial treatment. Graft excision and hardware removal is considered only for those infections resistant to initial treatment and for the infected allograft.

Does hepatocellular injury in sepsis involve apoptosis?

Apoptosis (AO) is a process by which cells typically undergo a form of nonnecrotic cellular suicide. AO normally allows the host to selectively delete cells from a given tissue site without producing bystander injury associated with necrosis. However, inappropriate induction of AO has been associated with a variety of acute as well as chronic pathological states and may contribute to the therapeutic nonresponsiveness frequently encountered in the septic animal/patient's organ function. In this respect, while AO has been demonstrated in a variety of immune cell tissues of septic animals it is unclear if it is present in the septic liver. Therefore, it was the aim of our study to determine if AO is evident in hepatocytes of polymicrobial septic animals. To assess this, C3H/HeN male mice were subjected to polymicrobial sepsis (cecal ligation and puncture) or sham- CLP (Sham). Hepatocytes were then harvested at 4 h (early hyperdynamic phase) or 24 h (late hypodynamic state) later, and indices of AO were assessed [cell cycle analysis of Annexin V/propidium iodide (PI) staining for flow cytometric analysis, DNA extracted, and cell death ELISA]. Plasma glutamic pyruvic transaminase (GPT) was also colorimetrically assessed as well as total viable cell yield as an index of hepatocellular necrosis. The results indicate that indices of hepatocellular AO, as determined by cell cycle analysis and cell death ELISA, were markedly increased in polymicrobial septic mice at 24 h. However, while an increase in DNA fragmentation/degradation could be consistently detected, the pattern was typically faint. Similarly, although there was an increase in Annexin V staining it was not dissociated from that of PI (necrotic index). Alternatively, necrosis (as evidenced by increased GPT levels at both 4 and 24 h) preceded the induction of all the indices of AO. Taken together, these data suggest a role for both necrosis and apoptosis in the evolution of hepatocellular injury encountered in the polymicrobial septic animal/patient which may represent a unique pattern of cell death under such conditions.

Increased mucosal B-lymphocyte apoptosis during polymicrobial sepsis is a Fas ligand but not an endotoxin-mediated process

Sepsis is reported to induce an increase in the rate of apoptosis (Ao), in immature lymphoid cells residing in hematopoietic tissues such as the thymus and bone marrow. Alternatively, secondary lymphoid tissue, such as the spleen exhibit little innate (unstimulated) Ao. However, it is unknown whether or not polymicrobial sepsis has any effects on the frequency of Ao in mucosal lymphoid tissue and what, if any, are the functional consequences of such a change. To assess this, Peyer's patch cells were harvested from C3H/HeN (endotoxin-sensitive) mice killed 12 or 24 hours after the onset of polymicrobial sepsis (cecal ligation and puncture [CLP]). The results indicate that the percentage of cells that were Ao+ as determined by flow cytometry were markedly increased at 24 hours, but not at 12 hours post-CLP. This correlates well with evidence of increased DNA fragmentation as well as histological changes observed both at a light and transmission electron microscopic level of the Peyer's patch Ao. Phenotypically, these changes were restricted to the B220+ (B-cell) population that also exhibited a marked increase of Fas/Apo-1 antigen expression. The functional consequence of this increased apoptosis appears to be associated with the endogenous stimulation (activation) of IgA production by mucosal B lymphocytes and increased nuclear c-Rel expression. Furthermore, we found that Peyer's patch lymphocytes isolated from C3H/HeJ-Faslgld (endotoxin-tolerant/Fas ligand- [FasL] deficient) as opposed to C3H/HeJ (endotoxin-tolerant) inbred mice did not exhibit increased Ao after CLP. These findings indicate that increased B-cell Ao appears to be a FasL-Fas antigen-mediated process, but is not due to endotoxin sensitivity. In conclusion, we speculate that the increased Fas-associated apoptosis detected in mucosal B cells (as opposed to splenic or bone marrow B cells) may be due to increased luminal antigens other than endotoxin, released due to gut barrier integrity breakdown during sepsis.

Occurrence and Partial Characterization of a New Mechanically Transmissible Virus in Mashua from the Ecuadorian Highlands

Mashua (Tropaeolum tuberosum) is a tuber crop indigenous to the Andean highlands and of economic value to its native people as a food and medicinal crop. Field plants often exhibit symptoms typical of virus infection, including interveinal chlorosis, leaf cupping, distortion, and stunting. Using an herbaceous host range, at least 1 mechanically transmissible virus was detected in each of 10 accessions. All virus isolates tested reacted to potyvirus group antiserum in indirect enzyme-linked immunosorbent assays (ELISA). Results of monoclonal antibody testing using antigen coated plate (ACP) ELISA, where virions are disrupted to expose cryptotopes, indicated that isolate Tt 4 has epitopes in common with maize dwarf mosaic potyvirus A (MDMV-A). Polyclonal antiserum produced to purified preparations of the Tt 4 isolate reacted in indirect ELISA to Tt 4, the common strain of potato potyvirus Y (PVY-C), less strongly to tobacco etch potyvirus (TEV) and potato potyvirus A (PVA), but not to 11 other potyviruses, including MDMV-A. Conversely, the Tt 4 isolate reacted strongly in indirect ELISA to antisera to bean common mosaic potyvirus (BCMV) and watermelon mosaic potyvirus 2 (WMV-2), but not antisera to 12 other potyviruses. Our data suggest that isolate Tt 4 is a distinct potyvirus closely related to and sharing external epitopes with PVY-C, TEV, PVA, WMV-2, and BCMV, and buried epitopes with MDMV-A. The virus has been tentatively named Tropaeolum mosaic potyvirus (TropMV). A survey of T. tuberosum in Ecuador revealed that TropMV was widespread, being detected by ACP-ELISA in 34 of 46 accessions at the National Institute for Agricultural Research's Santa Catalina Research Station, Quito, and all eight production fields surveyed.

Factors responsible for peritoneal granulocyte apoptosis during sepsis

Apoptosis (Ao), is a process by which cells undergo a form of non-necrotic cellular suicide, the control of which may have significant impact on host immunoresponsiveness to a septic challenge. The aim of this study was to determine (1) if Ao is evident in granulocytes harvested from the blood or peritoneum of septic animals and to what extent this was associated with cell activation and (2) whether the in vivo administration of the TNF inhibitor (TNFbp) alters this process. To assess the first aim, C3H/HeN male mice were subjected to polymicrobial sepsis [cecal ligation and puncture (CLP)] or sham-CLP (Sham) and sacrificed at 4 or 24 hr following CLP. Blood leukocytes and peritoneal exudate cells were harvested, stained with monoclonal fluorochrome-conjugated antibodies to granulocytes (Gr1), the activation marker ICAM-1, and either the cell cycle dye, 4',6-diamidino-2-phenylindole, or TUNEL assay (to assess the %Ao+), was used for two- and three-color flow cytometric analysis. Peritoneal exudate cells exhibited increased %Ao+ cells at both 4 and 24 hr post-CLP, while blood leukocytes showed a decrease in %Ao+ only at 24 hr. The increase in Ao in the peritoneum was evident only in the Gr1- cell population at 4 hr but was present in both Gr1+ and Gr1- cells at 24 h. Furthermore, the increase in the %Ao+ cells was associated with an increased % of ICAM-1 positive cells. To the extent that TNF affects the 24 hr induction of Ao in peritoneal exudate cells, mice were treated with either 250 micrograms TNFbp/mouse (s.c.) or vehicle control immediately following CLP. The results indicate that administration of TNFbp markedly decreased Gr1+ but not Gr1- cell Ao. Thus, not only does polymicrobial sepsis induce a marked early rise in phagocyte Ao associated with cell activation, but the increase in peritoneal granulocyte Ao, unlike macrophage Ao, is mediated by TNF and/or an agent released by TNF.