Studies on insects and mites causing galls on the leaves of common ash Fraxinus excelsior L. in the Ojców National Park in Poland

The occurrence frequency of galls caused by insects and mites on the leaves of Fraxinus excelsior L. was investigated, based on leaf samples collected in the Ojców National Park in 2000–2001. The species composition of galls was identical in two consecutive years. Galls were caused by 5 species a total of 2881 galls. The most numerous species was Dasineura fraxinea (Kieffer) in both years.Index of occurrence frequency and Agrell's index of species co-existence have been calculated. This index reached the highest values in case of Dasineura fraxinea and Vasates fraxini (Nalepa) in 2000 as well as D. fraxinea and Psyllopsis fraxini (L.) in 2001.     

Studies on insects and mites causing galls on the leaves of European aspenPopulus tremula L. in the Ojców National Park in Poland

Analytical studies were conducted on the species composition of galls occurring on the leaves of European aspen Populus tremula L. in the Ojców National Park in 1997–1998. The species composition of galls was similar in two consecutive years, i.e 6 and 7 species, respectively (a total of 5492 galls). The most numerous species wasPhyllocoptes populi Nalepa in both years. Index of occurrence frequency and Agrell’s index of species co-existence have been calculated. This index reached the highest values in both years in case ofHarmandia cavernosa (Rübsaamen) andH. tremulae Winnertz.     

Studies on insects and mites causing galls on the leaves of European aspenPopulus tremula L. in the Ojców National Park in Poland

Analytical studies were conducted on the species composition of galls occurring on the leaves of European aspen Populus tremula L. in the Ojców National Park in 1997–1998. The species composition of galls was similar in two consecutive years, i.e 6 and 7 species, respectively (a total of 5492 galls). The most numerous species wasPhyllocoptes populi Nalepa in both years. Index of occurrence frequency and Agrell’s index of species co-existence have been calculated. This index reached the highest values in both years in case ofHarmandia cavernosa (Rübsaamen) andH. tremulae Winnertz.     

What impact will EPPO's new resistance risk assessment guideline have on selection pressure in the European Union?

This paper examines practical and regulatory implications, including both costs and benefits, resulting from implementation of EPPO's new resistance risk analysis guideline. Crop-protection companies operating in Europe are preparing risk analyses and management strategies, and are monitoring for resistance. However, this is a complex and expensive process involving technical, commercial and regulatory functions. The actual cost of filling these data gaps is consequently greater than many would have anticipated. The agrochemical industry has a vested interest in managing resistance and is committed to maintaining the essential contribution of crop-protection products to sustainable agriculture. However, with increasing regulatory costs, it is important that regulatory authorities concentrate requirements for resistance risk analyses, management strategies and monitoring where these are most needed. Should these requirements be applied indiscriminately, crop-protection companies will have to consider whether or not it is economically justifiable to make these investments, or whether to remove less profitable uses from product labels. In such situations, minor crops stand to be disproportionately effected. One year after publication, it is too early to measure the guideline's impact on selection pressure. It is already clear that the guideline represents an unprecedented step forward in the regulation and harmonisation of resistance management. There are, however, valid arguments against regulation of resistance management. One of the most important criticisms that is levelled against the latter approach is that, with the best motivation and with appropriate use restrictions on labels, these actions alone do not solve the problem. It is critical that all stakeholders in the crop protection process are made aware of the importance of resistance management and of complying with prescribed strategies.     

Transdisciplinary weed research: new leverage on challenging weed problems?

Transdisciplinary weed research (TWR) is a promising path to more effective management of challenging weed problems. We define TWR as an integrated process of inquiry and action that addresses complex weed problems in the context of broader efforts to improve economic, environmental and social aspects of ecosystem sustainability. TWR seeks to integrate scholarly and practical knowledge across many stakeholder groups (e.g. scientists, private sector, farmers and extension officers) and levels (e.g. local, regional and landscape). Furthermore, TWR features democratic and iterative processes of decision‐making and collective action that aims to align the interests, viewpoints and agendas of a wide range of stakeholders. The fundamental rationale for TWR is that many challenging weed problems (e.g. herbicide resistance or extensive plant invasions in natural areas) are better addressed systemically, as a part of broad‐based efforts to advance ecosystem sustainability, rather than as isolated problems. Addressing challenging weed problems systemically can offer important new leverage on such problems, by creating new opportunities to manage their root causes and by improving complementarity between weed management and other activities. While promising, this approach is complicated by the multidimensional, multilevel, diversely defined and unpredictable nature of ecosystem sustainability. In practice, TWR can be undertaken as a cyclic process of (i) initial problem formulation, (ii) ‘broadening’ of the problem formulation and recruitment of stakeholder participants, (iii) deliberation, negotiation and design of an action agenda for systemic change, (iv) implementation action, (v) monitoring and assessment of outcomes and (vi) reformulation of the problem situation and renegotiation of further actions. Notably, ‘purposive’ disciplines (design, humanities and arts) have central, critical and recurrent roles in this process, as do integrative analyses of relevant multidimensional and multilevel factors, via multiple natural and social science disciplines. We exemplify this process in prospect and retrospect. Importantly TWR is not a replacement for current weed research; rather, the intent is to powerfully leverage current efforts.     

‘Candidatus Liberibacter solanacearum’ detected in Trioza urticae using suction trap-based monitoring of psyllids in Germany

Journal of Plant Diseases and Protection - Psyllids are small, phloem-feeding insects. Several species are vectors of economically important pathogens, such as ‘Candidatus Liberibacter...     

Life at the edge – the cytology and physiology of the biotroph to necrotroph transition in Hymenoscyphus fraxineus during lesion formation in ash

The progress of colonization of ash stems from ascospore inocula of Hymenoscyphus fraxineus was examined by light and electron microscopy. The main aim of the study was to characterize the cytology of the biotroph to necrotroph transition during lesion formation. Following direct penetration into epidermal cells, the fungus produced intracellular hyphae that invaded up to five cells before plant cells died. A lack of close attachment between the hyphal cell wall and plant cell membrane was revealed by plasmolysis of epidermal cells. Plant cells died at the centre of the infection but hyphae at the edge were typically found in living plant cells even around large lesions. During biotrophic invasion, the cytoplasm of penetrated plant cells showed very little response despite the plant cell membrane being in direct contact with the fungal cell wall. Before plant cell death, dark staining of the cytoplasm and proliferation of small vesicles was noted, but organelles retained normal ultrastructure. Dead plant cells contained dark brown, osmiophilic droplets. Penetration between epidermal or collenchyma cells was usually targeted to shared pits and involved constriction of hyphae. The transition to necrotrophy was not associated with a clear change in hyphal morphology. Biotrophic intracellular hyphae contained dense cytoplasm but hyphae in dead plant cells were more vacuolated. Remarkably little plant cell wall degradation was observed despite the fungus penetrating up to 18 cells deep into stem tissue. Features of the development of the ash dieback fungus are compared with other hemibiotrophic pathogens.     

Can poisons stimulate bees? Appreciating the potential of hormesis in bee–pesticide research

Hormesis, a biphasic dose response whereby exposure to low doses of a stressor can stimulate biological processes, has been reported in many organisms, including pest insects when they are exposed to low doses of a pesticide. However, awareness of the hormesis phenomenon seems to be limited among bee researchers, in spite of the increased emphasis of late on pollinator toxicology and risk assessment. In this commentary, we show that there are several examples in the literature of substances that are toxic to bees at high doses but stimulatory at low doses. Appreciation of the hormetic dose response by bee researchers will improve our fundamental understanding of how bees respond to low doses of chemical stressors, and may be useful in pollinator risk assessment. © 2015 Society of Chemical Industry     

Control of Farm Flies in Malta—III. The effect of residual insecticide sprays on Musca domestica and Stomoxys calcitrans in the Maltese Islands

Abstract

Field trials to control flies on animal farms in Malta were held during 1973 with tetrachlorvinphos, iodofenphos, fenitrothion, bioresmethrin and dimethoate applied as cover sprays to walls and ceilings. Results were assessed by fly population counts (using sticky fly-paper traps exposed for 24 h at weekly intervals), bioassay tests and visual assessments of flies on individual farms. Tetrachlorvinphos gave the best results and was applied as a cover spray on 12 large animal farms in the northwestern part of Gozo during 1974. Results, using the same criteria as in the 1973 trials, indicated that, although high fly mortality was observed and deposits on walls remained toxic throughout the season, effective control of houseflies and stableflies was not achieved.

It is suggested that residual spraying alone on the larger animal farms was not sufficient to overcome the breeding potential of the flies and that a residual spraying campaign could only be successful if more extensively applied and supplemented by a comprehensive programme of farm hygiene improvement.     

Aerial Spraying of Neemazal®-T/S Against the Forest Cockchafer (Melolontha hippocastani,Col.: Scarabaeidae) in South-West Germany: The Effects of Two Field Trials Performed in 2007 and 2008 on Local Populations

Journal of Plant Diseases and Protection - The forest cockchafer Melolontha hippocastani is a serious forest pest whose infestation levels have been increasing in South-West Germany since the...     

Studies on seed transmission of “Candidatus Liberibacter solanacearum” in pepper and its impact on plant emergence

“ Candidatus Liberibacter solanacearum” (Lso), transmitted by the potato psyllid (Bactericera cockerelli), is the causal agent of potato zebra chip, but can also infect other solanaceous plants, including peppers. Studies were conducted to investigate whether Lso could be transmitted to the next generation of plants through seeds from infected pepper plants. In 2014, jalapeno pepper plants were infested with psyllids carrying a mixture of Lso A and B (AB) at the AgriLife Research Station at Bushland. The study was again conducted in 2019 and pepper plants were infested with psyllids carrying Lso B or Lso AB. In each of the studies, noninfested plants served as controls. At harvest, fruits were collected and tested for the presence of Lso using quantitative PCR. Seeds from infected fruits were then tested for Lso. Overall, the percentage of seeds that tested positive for Lso ranged from 33% to 70%. However, Lso detection in embryos ranged only from 0% to 8%. Seed samples from Lso-positive fruits were planted in the greenhouse to determine the impact of Lso on emergence and the incidence of Lso in emerged plants. Although plant emergence differed between some of the seeds obtained from Lso-positive and -negative fruits, the overall impact of Lso on plant emergence was not consistent. However, of the 182 plants that emerged from seeds collected from infected fruits, none was positive for Lso, suggesting that seeds are unlikely to serve as sources for new Lso infections and their impact on disease epidemiology is negligible.     

How can research on pathogen population biology suggest disease management strategies? The example of barley scald (Rhynchosporium commune)

Barley scald fungus, Rhynchosporium commune, belongs to a host‐specialized species complex infecting grasses. Coalescent analyses of several genes indicate that R. commune originated c. 2500 years ago, after the domestication of barley. Phylogeographical analyses identified a diversity hotspot in Scandinavia, indicating an origin in northern Europe. After its emergence, R. commune became distributed globally on infected seeds, eventually invading the Fertile Crescent and infecting wild barley progenitors. Analyses of gene flow identified historical routes of migration out of Scandinavia and indicate a high degree of modern gene flow among South Africa, Australia and New Zealand. About 76% of global species diversity is found within barley fields, with all field populations showing a genetic structure consistent with sexual recombination. High levels of regional gene flow suggest wind‐dispersed ascospores and movement of infected seed. Quantitative traits, including pathogen aggressiveness, thermal sensitivity and fungicide resistance, showed high heritability and high levels of diversity within nine globally representative populations. Field experiments provided evidence for a fitness cost associated with complex virulence and a trade‐off between pathogenic and saprophytic fitness. All findings indicate that global R. commune populations have significant potential to evolve rapidly in response to environmental changes, including deployment of resistant cultivars, fungicide applications and global warming. Specific recommendations to improve management of barley scald include: (i) focus resistance breeding efforts in northern Europe, which offers the best location to screen germplasm and may provide useful sources of scald resistance; (ii) improve seed treatment, certification and quarantine programmes to limit long distance pathogen movement; (iii) manage barley stubble to decrease pathogen population size, limit production of sexual inoculum and reduce the pathogen's evolutionary potential.     

Rhabdocline needle cast—investigations on various Douglas fir tissue types

Douglas fir (Pseudotsuga menziesii) is one of the most important non-indigenous tree species in Germany. The species is characterized by a wide amplitude of growing conditions, and is of increasing interest, in particular from the perspective of climate change. Douglas fir is nevertheless particularly susceptible to fungal pathogens, such as Rhabdocline pseudotsugae . The aim of the present study was therefore to develop an early detection method for R. pseudotsugae based on the polymerase chain reaction (PCR). Existing molecular techniques were adapted and optimized to detect the pathogen in small sample volumes. Both healthy and infected Douglas firs were examined, with various tissue types (buds, cambial tissue, needles) and seeds tested for the presence of R. pseudotsugae. Non-infected Douglas firs did not give positive responses in the molecular analyses, but the pathogen was clearly detected in buds, cambial tissues, needles and seeds of infected trees. To date, the fungus has been considered an obligate biotrophic needle parasite. The present results provide clear evidence, however, for the existence of an endophytic stage in the life cycle of R. pseudotsugae. In contrast with previous studies, this paper investigates the dispersal of the fungus via seeds.     

Impacts of climate change on plant diseases—opinions and trends

There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases. This overview addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods.     

Exceeding the threshold value for Trioza apicalis Förster 1848 in carrot fields did not cause damage as revealed during monitoring in Germany from 2017–2020

Journal of Plant Diseases and Protection - The carrot psyllid Trioza apicalis Förster 1848 is a carrot pest in Europe that can cause serious damages in case of massive occurrence. Damages up...     

Pirimiphos‐methyl in the control of Psara bipunctalis F. on Amaranthus cruentus in Southern Nigeria

Abstract

Psara bipunctalis F. (Lepidoptera. Pyralidae) has been identified as a serious defoliating insect pest of Amaranthus cruentus in the southern part of Nigeria. A brief life cycle study carried out at ambient temperature of 28 C showed four different larval instars with pre‐pupal and pupal stages all lasting between 21 and 22 days. Three concentrations of primiphos‐methyl were evaluated for the control of P. bipunctalis in the field. Pirimiphos‐methyl at 0.57 kg/ha a.i. gave the optimal control of this defoliator.