Trap colour,size, and borders alter catches of Bactericera cockerelli in a potato crop

Visual cues play a key role in host finding in many phytophagous insects, including the tomato potato psyllid (TPP), Bactericera cockerelli (?ulc) (Hemiptera: Triozidae), a serious pest of solanaceous crops. This study evaluated the response of TPP to sticky traps of one of three colours, up to four sizes, and with or without green borders in an organic potato crop in Hawke's Bay, New Zealand. On average, large traps caught a higher density of TPP than small traps (with or without border; 25 and 14 TPP per 100 cm², respectively). Tomato potato psyllid density on the green border was affected by the colour of the centre trap; a blue centre resulted in substantially fewer TPP on the green border than a yellow centre (9.0 vs. 69.6 TPP per 100 cm²). Trap catches in early summer were male biased, whereas catches of male and female TPP in late summer were approximately equal.     

Feeding disruption of potato psyllid,Bactericera cockerelli,by imidacloprid as measured by electrical penetration graphs

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a serious pest of potatoes that can cause yield loss by direct feeding and by transmitting a bacterial pathogen, Candidatus Liberibacter psyllaurous (also known as Candidatus L. solanacearum), which is associated with zebra chip disease of this crop. Current pest management practices rely on the use of insecticides for control of potato psyllid to lower disease incidences and increase yields. Imidacloprid is typically applied at potato planting, and it remains unknown if imidacloprid has any effect on potato psyllid feeding behavior. Thus, our specific objectives of this study were to determine and characterize the effects of imidacloprid treatment (0.11 ml l^?1) to potato plants on adult potato psyllid feeding behavior 1, 2, and 4 weeks post‐application. Electrical penetration graph (EPG) recordings of potato psyllid feeding revealed six EPG waveforms, which include non‐probing (NP), intercellular stylet penetration (C), initial contact with phloem tissue (D), salivation into phloem sieve elements (E1), phloem sap ingestion (E2), and ingestion of xylem sap (G). The number of NP events and the duration of individual NP events significantly increased on plants treated with imidacloprid compared with untreated controls. Potato psyllids exhibited significant decreases in the number of phloem salivation events on plants treated with imidacloprid. Waveform durations and waveform durations per event for E2 and G were significantly decreased for psyllids on plants treated with imidacloprid compared with untreated controls. These data suggest that the effective use of imidacloprid to reduce transmission of Ca. Liberibacter psyllaurous is related to the negative effects of imidacloprid on psyllid feeding.     

Invasion of Colorado potato beetle,Leptinotarsa decemlineata,in China: dispersal,occurrence, and economic impact

Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is a global destructive pest of potato, Solanum tuberosum L. (Solanaceae). It is also an important quarantine pest in China, but its dispersal history, occurrence, and economic impact in China have not yet been reported. We determined the current distribution of CPB and reconstructed its dispersal routes. We also investigated the density of CPB in China in 2006, 2007, 2009, and 2010, and estimated the economic impact of CPB in China. In 1993, CPB was first detected in Xinjiang and subsequently spread eastward. The CPB entered China at three distinct points in Xinjiang: in Huocheng County, Tacheng City, and Habahe County. As of 2010, CPB had invaded 38 counties and cities in China, with a distribution area of 277 000 km², between 42°40′–48°28′N and 80°15′–90°41′E. The distribution area could be divided into four zones (from south to north): Ili River Valley, northern slope of the Tianshan Mountains, Tacheng Basin, and Altay. The average annual dispersal rates in the four zones were 18, 45, 12, and 24 km year^?1, respectively. In China, CPB seriously damages potato, impacts eggplant, Solanum melongena L., and occasionally harms tomato, Solanum lycopersicum L. The current annual economic loss caused by CPB in China is estimated to be 3.2 million USD. The potential annual economic losses after completion of its invasion in China is estimated to be 235 million USD. Future invasion pathways, factors affecting CPB dispersal, and control measures were discussed.     

Stylet penetration activities linked to the acquisition and inoculation of Candidatus Liberibacter solanacearum by its vector tomato potato psyllid

The tomato potato psyllid (TPP), Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is the main vector of the bacterium Candidatus Liberibacter solanacearum (Lso), a major disease of solanaceous crops. Feeding of TPP is associated with Lso transmission. However, very little is known about the stylet penetration activities linked to acquisition and inoculation of Lso. The electrical penetration graph (EPG)‐DC system was used to monitor stylet penetration activities during acquisition and inoculation of Lso by individual TPP on tomato [Solanum lycopersicum L. (Solanaceae)]. Female TPP from Lso‐free and Lso‐infected colonies were used in acquisition and inoculation tests, respectively. In the acquisition tests, TPP were tested for Lso after EPG recording of their stylet penetration activities on Lso‐infected tomato shoots. In the inoculation tests, samples from the tomato plants on which the stylet penetration of Lso‐infected TPP had been recorded were tested for Lso infection. The relationships between qPCR results and the EPG waveforms (C, G, D, E1, and E2) representing the main stylet penetration activities performed by individual insects in inoculation and acquisition tests were investigated. Results confirmed that a single adult TPP is capable of infecting a plant with Lso. Our data suggest that acquisition of the bacteria occurs during phloem ingestion (E2), and inoculation is likely associated with salivation into the phloem sieve elements (E1). The durations of EPG parameters were not significantly different between Lso‐infected and Lso‐free TPP (later shown by qPCR) in acquisition tests. In inoculation tests, the durations of E1 or E2 recorded from TPP on Lso‐infected and Lso‐free plants that were later shown by qPCR were not significantly different. However, C was shorter on Lso‐infected plants than on Lso‐free plants, where TPP performed phloem activities. The minimum plant access period required for Lso transmission by a single TPP was estimated to be ca. 2 h, with an acquisition threshold of about 36 min.     

Photosynthetic responses of potato to Colorado potato beetle injury and differences in injury between adult males and females

Establishing rates of injury to plants and the physiological impact of this injury provides essential data in the development of economic injury levels, but variation of sex effects is not often considered. Here, we examined injury by the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), larvae and adult males and females on potato, Solanum tuberosum L. (Solanaceae). Specifically, we looked for adult sex differences between males and females in injury rates (= leaf consumption rates), and examined the impact of all types of injury (larval, adult male, and adult female) on gas exchange parameters of remaining potato leaf tissue. Experiments were conducted in the field and in growth chambers on Frito‐Lay proprietary and Pike chipping‐potato varieties at pre‐blooming and blooming stages. We found no change in photosynthetic rates on remaining (uninjured) leaf tissue infested with male, female, or fourth‐stage larva of Colorado potato beetle. However, when the midrib was cut in trials with male beetles, the remaining tissue above the injury exhibited photosynthetic rate reductions as a result of stomatal limitations. These findings are consistent with the pattern that we and other researchers have observed with gross tissue removal by various insects on other plant species. Adult females consumed more tissue than males, and temperature was positively correlated with feeding rates for both sexes. Sex‐related differences in feeding rate are most important to studies quantifying consumption rates for economically important species because of its potential impact on resulting economic injury level calculations.     

Genetic assignment of recruits reveals short‐ and long‐distance larval dispersal in Pocillopora damicornis on the Great Barrier Reef

Understanding connectivity of coral populations among and within reefs over ecologically significant timescales is essential for developing evidence‐based management strategies, including the design of marineprotected areas. Here, we present the first assessment of contemporary connectivity among populations of two Molecular Operational Taxonomic Units (MOTUs) of the brooding coral Pocillopora damicornis. We used individual‐based genetic assignment methods to identify the proportions of philopatric and migrant larval recruits, settling over 12 months at sites around Lizard Island (northern Great Barrier Reef [GBR]) and over 24 months at sites around the Palms Islands (central GBR). Overall, we found spatially and temporally variable rates of self‐recruitment and dispersal, demonstrating the importance of variation in local physical characteristics in driving dispersal processes. Recruitment patterns and inferred dispersal distances differed between the two P. damicornis MOTUs, with type α recruits exhibiting predominantly philopatric recruitment, while the majority of type β recruits were either migrants from identified putative source populations or assumed migrants based on genetic exclusion from all known populations. While P. damicornis invests much energy into brooding clonal larvae, we found that only 15% and 7% of type α and type β recruits, respectively, were clones of sampled adult colonies or other recruits, challenging the hypothesis that reproduction is predominantly asexual in this species on the GBR. We explain high rates of self‐recruitment and low rates of clonality in these MOTUs by suggesting that locally retained larvae originate predominantly from spawned gametes, while brooded larvae are mainly vagabonds.     

No evidence of sex‐biased dispersal in an island population of Common Blackbirds Turdus merula

Natal dispersal has major consequences for the dynamics and genetic structure of populations. Female‐biased natal dispersal, otherwise the norm in birds, is overridden when the place to move is limited, as on isolated islands. This effect was confirmed for the fist time in a European study system, the Common Blackbird breeding on Heligoland Island. Spatially restricted and sexually uniform natal dispersal may be a prerequisite for successful establishment of populations on remote islands or isolated habitat fragments, and this could play a major role in speciation processes.     

Functional analysis of endo‐1,4‐β‐glucanases in response to Botrytis cinerea and Pseudomonas syringae reveals their involvement in plant–pathogen interactions

Plant cell wall modification is a critical component in stress responses. Endo‐1,4‐β‐glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence‐signalling network. A study of a set of Arabidopsis EG T‐DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant–pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant–pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.     

Association mapping of cold‐induced sweetening in potato using historical phenotypic data

In this study, historical phenotypic data from a potato breeding programme were used with an association mapping approach to identify alleles of candidate genes associated with cold‐induced sweetening of potato. Molecular marker analysis was used to determine allelic variation of candidate genes potentially involved in cold‐induced sweetening. Variations in the UDP‐glucose pyrophosphorylase (UGPase, EC 2.7.7.9) and apoplastic invertase genes (EC 3.2.1.26) were significantly associated with cold‐induced sweetening, and a possible interaction of apoplastic invertase and apoplastic invertase inhibitor was identified. This demonstrates that breeding programme phenotypic data collected over multiple years and environments can be used successfully with pedigree information for association mapping. It also confirms that the UGPase and apoplastic invertase markers are transferable across breeding programmes with distinct germplasm.     

Contributions of long‐distance dispersal to population growth in colonising Pinus ponderosa populations

Long‐distance dispersal is an integral part of plant species migration and population development. We aged and genotyped 1125 individuals in four disjunct populations of Pinus ponderosa that were initially established by long‐distance dispersal in the 16th and 17th centuries. Parentage analysis was used to determine if individuals were the product of local reproductive events (two parents present), long‐distance pollen dispersal (one parent present) or long‐distance seed dispersal (no parents present). All individuals established in the first century at each site were the result of long‐distance dispersal. Individuals reproduced at younger ages with increasing age of the overall population. These results suggest Allee effects, where populations were initially unable to expand on their own, and were dependent on long‐distance dispersal to overcome a minimum‐size threshold. Our results demonstrate that long‐distance dispersal was not only necessary for initial colonisation but also to sustain subsequent population growth during early phases of expansion.     

Temperature responses of a plant‐insect system using a food‐web performance approach

Evaluation of the performance of a plant‐herbivore system as a whole is difficult due to the lack of fitness parameters that can be applied to both components. The individual use of traditional measures of performance (e.g., r_m, biomass) can provide useful, but incomplete information on the performance of insect herbivores and seldom incorporates plant performance. We propose the use of the net generational productivity (NGP) to evaluate the fitness of the herbivore, which can then be compared directly with the performance of the plant in biomass units, to obtain the food‐web performance ratio (φ_H/P). We compared three biotypes of the potato aphid, Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae), when raised on three different host plants: potato (Solanum tuberosum L. cv. Norland) and two bell peppers (Capsicum annuum L. cv. Fascinato and cv. Crosby) (all Solanaceae) at temperatures ranging from 8 to 36 °C. The temperature profiles of the potato aphid biotypes suggest that this aphid is better suited to temperate climates, and its performance generally depends on the particular host‐plant/biotype association. Plant growth performance showed that potato has a lower thermal tolerance, but has a faster growth rate than bell peppers, especially in the range of 16–24 °C. Temperature variation in the φ_H/P ratio shows that aphids have a greater performance than plants, especially at lower temperatures, at which they can accumulate biomass up to 148 times faster. Because of the aphid's biological inability to withstand long exposures to temperatures above 28 °C, plants have a slight advantage over aphids. Nonetheless, as the performance of plants is extremely reduced at high temperatures, this advantage cannot withstand long‐term exposures to extreme temperatures. This is the first attempt to obtain a parameter capable of determining the climatic profile and performance of a food web in an inclusive yet simple manner.     

The role of immigration and local adaptation on fine‐scale genotypic and phenotypic population divergence in a less mobile passerine

Dispersal and local patterns of adaptation play a major role on the ecological and evolutionary trajectory of natural populations. In this study, we employ a combination of genetic (25 microsatellite markers) and field‐based information (seven study years) to analyse the impact of immigration and local patterns of adaptation in two nearby (< 7 km) blue tit (Cyanistes caeruleus) populations. We used genetic assignment analyses to identify immigrant individuals and found that dispersal rate is female‐biased (72%). Data on lifetime reproductive success indicated that immigrant females produced fewer local recruits than their philopatric counterparts whereas immigrant males recruited more offspring than those that remained in their natal location. In spite of the considerably higher immigration rates of females, our results indicate that, in absolute terms, their demographic and genetic impact in the receiving populations is lower than that in immigrant males. Immigrants often brought novel alleles into the studied populations and a high proportion of them were transmitted to their recruits, indicating that the genetic impact of immigrants is not ephemeral. Although only a few kilometres apart, the two study populations were genetically differentiated and showed strong divergence in different phenotypic and life‐history traits. An almost absent inter‐population dispersal, together with the fact that both populations receive immigrants from different source populations, is probably the main cause of the observed pattern of genetic differentiation. However, phenotypic differentiation (P_ST) for all the studied traits greatly exceeded neutral genetic differentiation (F_ST), indicating that divergent natural selection is the prevailing factor determining the evolutionary trajectory of these populations. Our study highlights the importance of integrating individual‐ and population‐based approaches to obtain a comprehensive view about the role of dispersal and natural selection on structuring the genotypic and phenotypic characteristics of natural populations.     

Resistance gene enrichment sequencing (RenSeq) enables reannotation of the NB‐LRR gene family from sequenced plant genomes and rapid mapping of resistance loci in segregating populations

RenSeq is a NB‐LRR (nucleotide binding‐site leucine‐rich repeat) gene‐targeted, Resistance gene enrichment and sequencing method that enables discovery and annotation of pathogen resistance gene family members in plant genome sequences. We successfully applied RenSeq to the sequenced potato Solanum tuberosum clone DM, and increased the number of identified NB‐LRRs from 438 to 755. The majority of these identified R gene loci reside in poorly or previously unannotated regions of the genome. Sequence and positional details on the 12 chromosomes have been established for 704 NB‐LRRs and can be accessed through a genome browser that we provide. We compared these NB‐LRR genes and the corresponding oligonucleotide baits with the highest sequence similarity and demonstrated that ~80% sequence identity is sufficient for enrichment. Analysis of the sequenced tomato S. lycopersicum ‘Heinz 1706’ extended the NB‐LRR complement to 394 loci. We further describe a methodology that applies RenSeq to rapidly identify molecular markers that co‐segregate with a pathogen resistance trait of interest. In two independent segregating populations involving the wild Solanum species S. berthaultii (Rpi‐ber2) and S. ruiz‐ceballosii (Rpi‐rzc1), we were able to apply RenSeq successfully to identify markers that co‐segregate with resistance towards the late blight pathogen Phytophthora infestans. These SNP identification workflows were designed as easy‐to‐adapt Galaxy pipelines.     

Long‐distance dispersal and genetic structure of natural populations: an assessment of the inverse isolation hypothesis in peat mosses

It is well accepted that the shape of the dispersal kernel, especially its tail, has a substantial effect on the genetic structure of species. Theory predicts that dispersal by fat‐tailed kernels reshuffles genetic material, and thus, preserves genetic diversity during colonization. Moreover, if efficient long‐distance dispersal is coupled with random colonization, an inverse isolation effect is predicted to develop in which increasing genetic diversity per colonizer is expected with increasing distance from a genetically variable source. By contrast, increasing isolation leads to decreasing genetic diversity when dispersal is via thin‐tailed kernels. Here, we use a well‐established model group for dispersal biology (peat mosses: genus Sphagnum) with a fat‐tailed dispersal kernel, and the natural laboratory of the Stockholm archipelago to study the validity of the inverse isolation hypothesis in spore‐dispersed plants in island colonization. Population genetic structure of three species (Sphagnum fallax, Sphagnum fimbriatum and Sphagnum palustre) with contrasting life histories and ploidy levels were investigated on a set of islands using microsatellites. Our data show (, amova , IBD) that dispersal of the two most abundant species can be well approximated by a random colonization model. We find that genetic diversity per colonizer on islands increases with distance from the mainland for S. fallax and S. fimbriatum. By contrast, S. palustre deviates from this pattern, owing to its restricted distribution in the region, affecting its source pool strength. Therefore, the inverse isolation effect appears to hold in natural populations of peat mosses and, likely, in other organisms with small diaspores.