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     

Does genetic variability in weeds respond to non‐chemical selection pressure in arable fields?

At a time when herbicide use is being challenged by the selection of herbicide‐resistant weeds, reliance on other, innovative weed control strategies is becoming increasingly necessary. However, one may question the sustainability of these novel farming practices if weeds adapt rapidly to these non‐chemical selection pressures. Although farmers and agronomists impose many selective processes through farming practices, there is a paucity of literature demonstrating these selection cases in arable fields. In contrast to the relatively simple case of herbicide resistance, random trait association and variability in selection pressures in field conditions could explain why there are so few clear examples of adaptive processes to non‐chemical control in arable fields.     

Regulated non‐quarantine pests: fact or fiction?

A new category of officially regulated pests has been introduced during the past decade. The aim of this new categorization is to protect plant health and, in particular, farmers’ and growers’ crops against the introduction of pests via propagation material. The phytosanitary term ‘regulated non‐quarantine pests’ (RNQPs) is relatively new. It was introduced in 1997 as part of the new revised text of the International Plant Protection Convention. These RNQPs differ from the common category of quarantine pests in that they can be widespread within the territory of concern. Unlike quarantine pests, a level of tolerance could be applied for RNQPs infesting certain plants for planting. Some certification systems for the production of propagation material may specify certain tolerance levels, however, these systems are usually not regulated by national plant protection organizations and the tolerance levels are usually not based on scientific evidence. To date, only a few countries have applied the concept of RNQPs: notably Uruguay and Brazil. To apply the concept and, in particular, to determine specific tolerance levels presents many challenges. The concept may be embraced in the coming years by the European Community as part of the revision of the EU Council Directive 2000/29/EC.     

(Q)SAR tools for the prediction of mutagenic properties: Are they ready for application in pesticide regulation?

The assessment of human health risks resulting from the presence of metabolites in groundwater and food residues has become an important element in pesticide authorisation. In this context, the evaluation of mutagenicity is of particular interest and a paradigm shift from exposure‐triggered testing to in silico‐based screening has been recommended in the European Food Safety Authority (EFSA) Guidance on the establishment of the residue definition for dietary risk assessment. In addition, it is proposed to apply in silico predictions when experimental mutagenicity testing is not possible due to a lack of sufficient quantities of the pesticide metabolite. This, combined with animal welfare and economic considerations, has led to a situation where an increasing number of in silico studies are submitted to regulatory authorities. Whilst there is extensive experience with in silico predictions for mutagenicity in the chemical and pharmaceutical industry, their suitability in pesticide regulation is still insufficiently considered. Therefore, we herein discuss critical issues that need to be resolved to successfully implement (Quantitative) Structure‐Activity Relationship ((Q)SAR) as an accepted tool in pesticide regulation. For illustration purposes, the results of a pilot study are included. The presented study highlights a need for further improvement regarding the predictivity and applicability domain of (Q)SAR systems for pesticides and their metabolites, but also raises other questions such as model selection, establishment of acceptance criteria, harmonised approaches to the combination of model outputs into overall conclusions, adequate reporting and data sharing. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Is the current state of the art of weed monitoring suitable for site‐specific weed management in arable crops?

Weed monitoring is the first step in any site‐specific weed management programme. A relatively large variety of platforms, cameras, sensors and image analysis procedures are available to detect and map weed presence/abundance at various times and spatial scales. Remote sensing from satellites or aircraft can provide accurate weed maps when the images are obtained at late weed phenological stages. Cameras located on unmanned aerial vehicles (UAVs) have been shown to be adequate for early‐season weed detection in a variety of wide‐row crops, providing images with relatively high spatial resolutions. Alternatively, weed detection/mapping systems from ground‐based platforms can achieve even higher resolutions using a variety of non‐imaging and imaging technologies. These ground systems are suited, in some cases, for real‐time site‐specific weed management. Despite this rich arsenal of technologies, their commercial adoption is, apparently, low. In this study, we describe the state of the art of remotely sensed and ground‐based weed monitoring in arable crops and the current level of adoption of these technologies, exploring major constraints for adoption and trying to identify research gaps and bottlenecks.     

Are we analysing knockdown in the right way? how independence of the knockdown-recovery process from mortality may affect measures for behavioural effects in pesticide bioassays

In pesticide bioassays, especially those with neurotoxic agents, effects on animals are typically grouped into classes according to behaviour, such as normal and affected behaviour, which may range from unstable walking behaviour, to unable to move, to mortality. Generally, recovery is observed in all these effect classes, except the last. Mortality, however, disturbs the analysis of the recovery processes because it decreases the number of animals that otherwise could have shown a reversible effect. We consider that this interaction between mortality and other, reversible, effects is a conceptual problem, and give arguments in favour of analysing changes in behaviour and mortality as two independent, simultaneously occurring neurotoxic syndromes. As an illustration, two data sets are analysed in both ways and these show that marked differences may exist between conclusions reached by the two viewpoints. The consequences thereof are discussed in relation to toxico-kinetic explanations for neurotoxicant effects on behaviour and mortality. © 1999 Society of Chemical Industry     

Are herbicide‐resistant crops the answer to controlling Cuscuta?

BACKGROUND: Herbicide‐resistant crop technology could provide new management strategies for the control of parasitic plants. Three herbicide‐resistant oilseed rape (Brassica napus L.) genotypes were used to examine the response of attached Cuscuta campestris Yuncker to glyphosate, imazamox and glufosinate. Cuscata campestris was allowed to establish on all oilseed rape genotypes before herbicides were applied. RESULTS: Unattached seedlings of C. campestris, C. subinclusa Durand & Hilg. and C. gronovii Willd. were resistant to imazamox and glyphosate and sensitive to glufosinate, indicating that resistance initially discovered in C. campestris is universal to all Cuscuta species. Glufosinate applied to C. campestris attached to glufosinate‐resistant oilseed rape had little impact on the parasite, while imazamox completely inhibited C. campestris growth on the imidazolinone‐resistant host. The growth of C. campestris on glyphosate‐resistant host was initially inhibited by glyphosate, but the parasite recovered and resumed growth within 3–4 weeks. CONCLUSION: The ability of C. campestris to recover was related to the quality of interaction between the host and parasite and to the resistance mechanism of the host. The parasite was less likely to recover when it had low compatibility with the host, indicating that parasite‐resistant crops coupled with herbicide resistance could be highly effective in controlling Cuscuta. Published 2009 by John Wiley & Sons, Ltd.     

Is acetyl/butyrylcholine specificity a marker for insecticide‐resistance mutations in insect acetylcholinesterase?

Substrate specificity has been widely studied in vertebrate cholinesterases and it has been shown that two phenylalanines in the acyl pocket of acetylcholinesterase govern the acceptance of the acetyl/butyryl moiety of the choline esters. As an insecticide‐resistance mutation has been evidenced in the acyl pocket of Drosophila melanogaster and Musca domestica acetylcholinesterase we investigated the possibility of linking changes in acetyl/butyrylthiocholine specificity with mutations in insect acetylcholinesterase. We thus analyzed the effect of 28 mutations in Drosophila enzyme on acetyl/butyrylthiocholine, N‐methyl/N‐propyl‐carbamates and ethyl/methyl‐paraoxon preference. It appeared that the highest changes on acetyl/butyrylthiocholine and N‐propyl/N‐methyl‐carbamates preference were due to mutations in the acyl pocket. Nevertheless, other insecticide‐resistance mutations, not located in the acyl pocket, also modified these substrate preferences. Moreover, the effect of mutations in the acyl pocket was hidden when some other insecticide‐resistance mutations were combined in the enzyme. Consequently, acetyl/butyrylthiocholine preference alteration cannot be used as a marker to localize a mutation in the insect AChE. © 2000 Society of Chemical Industry     

Are road verges corridors for weed invasion? Insights from the fine‐scale spatial genetic structure of Raphanus raphanistrum

Raphanus raphanistrum (Brassicaceae) is considered amongst the world's worst agricultural weeds. We address critical issues in its management by studying the pathway of colonisation at local scales. For this, we assessed the small‐scale spatial genetic structure of 231 samples collected from three different sites across the Cape Floristic Region, South Africa, using 11 nuclear microsatellite markers. Although natural pollen and seed dispersal were expected to be restricted, we found no significant relationship between genetic and geographical distance within sites. Instead, our results suggest that R. raphanistrum had colonised new habitats via jump dispersal, rather than through natural diffusive dispersal at local scales. We did not find evidence for road verges as dispersal corridors, as evidenced by a lack of isolation‐by‐distance at local scales. Instead, the absence of spatial genetic structure suggests that R. raphanistrum had rapidly spread throughout its current range, possibly facilitated by human‐mediated actions. Management plans addressing containment or suppression of the weedy species R. raphanistrum (and possibly other weedy species) should take the high degree of connectivity between distant geographical localities into account.     

Plant pathogenic bacteria in open irrigation systems: what risk for crop health?

The current global area equipped for irrigation provides 30–40% of the world's gross food output. Water used for plant irrigation may harbour plant pathogens and foster their spread. This represents a serious risk for crop health, with heavy socio‐economic consequences. More specifically to plant pathogenic bacteria (PPB), a range of species have been reported from irrigation systems and their potential role in epidemic development has long been recognized. However, only a few studies have been performed to date on the ecology of PPB in the context of water habitats. Consequently, current knowledge of the biology, ecology and epidemiology of PPB in irrigation water is poor. In light of this, an attempt is made to describe the most relevant information concerning the role of open irrigation systems in the survival and dissemination of PPB throughout the range of cultivations and the possible consequences for crop health. The information described in this paper will help to improve understanding on the overlooked role of irrigation water as a reservoir of PPB.     

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.     

Can the parasitic weeds Striga asiatica and Rhamphicarpa fistulosa co‐occur in rain‐fed rice?

Striga asiatica and Rhamphicarpa fistulosa are important parasitic weeds of rain‐fed rice, partly distributed in similar regions in sub‐Saharan Africa (SSA). It is not evident whether their ecologies are mutually exclusive or partially overlapping. In Kyela, a rice‐growing area in south Tanzania where both parasites are present, three transects of about 3 km each across the upland–lowland continuum were surveyed in June 2012 and 2013. A total of 36 fields were categorised according to their position on the upland–lowland continuum as High, Middle or Low and soil samples were taken. In each field, parasitic and non‐parasitic weed species were identified in three quadrats. Additionally, in two pot experiments with four different moisture levels ranging from wilting point to saturation, influence of soil moisture on emergence and growth of parasites was investigated. Striga asiatica was observed in higher lying drier fields, while R. fistulosa was observed in the lower lying wetter fields. Furthermore, non‐parasitic weed species that were exclusive to S. asiatica‐infested fields are adapted to open well‐drained soils, while species that were exclusive to R. fistulosa fields are typical for wet soils. The experiments confirmed that S. asiatica is favoured by free‐draining soils and R. fistulosa by waterlogged soils. These results imply that changes in climate, specifically moisture regimes, will be crucial for future prevalence of these parasitic weeds. The non‐overlapping ecological range between their habitats suggests that their distribution and associated problems might remain separate. Thus, management strategies can be focused independently on either species.     

Phenological adaptation in weeds—an evolutionary response to the use of herbicides?

The possibility of phenological adaptation in weed species is discussed in terms of an evolved response to herbicide use. Weed populations often exhibit heritable variation in life history traits that may reflect phenological adaptations. Approaches to assessing ‘adaptedness’ are discussed. Selection for seed dormancy in a grass weed is considered through life history analysis. It is concluded that too little is known about both life histories and fitness of weed species in varying environments for conclusions to be drawn concerning phenological adaptation for use in herbicide resistance management. ©1997 SCI     

Integrated weed management (IWM): why are farmers reluctant to adopt non‐chemical alternatives to herbicides?

Implementation of integrated weed management (IWM) has been poor, with little evidence of concomitant reductions in herbicide use. Non‐chemical methods are often adopted as a means of compensating for reduced herbicide efficacy, due to increasing resistance, rather than as alternatives to herbicides. Reluctance to adopt non‐chemical methods is not due to a lack of research or technology but to a lack of farmer motivation and action. Justifiably, herbicides are often seen as the easier option – their convenience outweighs the increased complexity, costs and management time associated with non‐chemical alternatives. Greater use of non‐chemical alternatives to herbicides will only occur if the following seven aspects are addressed: (i) better recognition of the reasons why farmers are reluctant to use non‐chemical alternatives; (ii) encouraging farmers to adopt a longer‐term approach to weed control; (iii) changing farmers' attitudes to pesticides; (iv) paying more attention to the individual farmer's perspective; (v). greater involvement of economists, social scientists and marketing professionals; (vi) re‐evaluating research and extension priorities; and (vii) changing the mindset of funders of research and extension. If ‘persuasion’ fails to deliver greater implementation of IWM, authorities may resort to greater use of financial and other incentives combined with tougher regulations. © 2018 Society of Chemical Industry