Conserving the efficacy of insecticides against Plutella xylostella (L.) (Lep., Plutellidae)

Abstract:  The diamondback moth (DBM), Plutella xylostella (L.) (Lep., Plutellidae), is one of the most destructive insect pests of crucifers worldwide. It was the first crop insect reported to be resistant to DDT and now in many crucifer-producing regions it has shown significant resistance to almost every insecticide applied in field including biopesticides such as crystal toxins from Bacillus thuringiensis and spinosyns from Saccharopolyspora spinosa . In certain parts of the world, economical production of crucifers has become almost impossible because of its resistance to insecticides and resulting control failure. A coordinated resistance management program needs to be implemented with the involvement of pesticide industry, local pesticide regulatory authorities, scientists and farmers. The judicious use of chemicals in conjunction with other control measures (e.g. biological control agents, resistant varieties, proper fertilization rates) is the best way to manage DBM and other pests of cruciferous crops. Introduction of glucosinolate-sulphatase inhibitors as plant-incorporated-products or sprayable material may also lead to a novel pest management strategy.     

Can microbial-based insecticides replace chemical pesticides in agricultural production?

Extensive use of chemical insecticides to control insect pests in agriculture has improved yields and production of high-quality food products. However, chemical insecticides have been shown to be harmful also to beneficial insects and many other organisms like vertebrates. Thus, there is a need to replace those chemical insecticides by other control methods in order to protect the environment. Insect pest pathogens, like bacteria, viruses or fungi, are interesting alternatives for production of microbial-based insecticides to replace the use of chemical products in agriculture. Organic farming, which does not use chemical pesticides for pest control, relies on integrated pest management techniques and in the use of microbial-based insecticides for pest control. Microbial-based insecticides require precise formulation and extensive monitoring of insect pests, since they are highly specific for certain insect pests and in general are more effective for larval young instars. Here, we analyse the possibility of using microbial-based insecticides to replace chemical pesticides in agricultural production.     

Sampling a weighted pest complex: caterpillars in North Korean cabbage (Brassica oleracea var. capitata) crops

The lepidopteran pests Plutella xylostella L. (Plutellidae) and Pieris rapae L. (Pieridae: Pierini) are responsible for major yield losses of cabbage, Brassica oleracea L. (Brassicaceae), in North Korea. Preliminary integrated pest management (IPM) programmes using economic thresholds (ETs) to schedule insecticide applications have proved promising and have demonstrated marked increases in yield compared to standard farming practice, which relies heavily on synthetic insecticides. To use ETs effectively on a routine basis, farmers need efficient yet sufficiently precise methods of surveying crops for pests. Here we construct and validate binomial sequential sampling plans for the two-species pest complex and for P. rapae alone. The recommended plans would be practical to implement, demanding maximum sample sizes below 50 plants, and proved very slightly conservative with respect to classifying the population relative to the ET (i.e., they were slightly more likely to suggest control at the ET than not).     

天敌昆虫抗药性研究进展

天敌昆虫抗药性研究在协调害虫化学防治和生物防治中有着重要的理论和现实意义,其研究的最终目的在于更好地推进抗性天敌在害虫综合治理(IPM)中的应用。抗药性天敌昆虫具有潜在的巨大价值。鉴于此,本文系统地综述了天敌昆虫抗药性最新研究进展,包括杀虫剂对天敌昆虫的影响、天敌昆虫抗药性现状、抗药性机理和限制天敌昆虫抗药性发展因素等。文章最后还对抗药性天敌昆虫的应用前景进行了展望。     

Managing resistance with multiple pesticide tactics: theory, evidence, and recommendations

Sequences, mixtures, rotations, and mosaics are potential strategies for using more than one pesticide to manage pest populations and for slowing the evolution of pesticide resistance. Results from theoretical models suggest that, under certain conditions, mixtures might be especially effective for resistance management. The assumptions of such models, however, are probably not widely applicable. Potential disadvantages associated with mixtures that are usually not considered in modeling studies include disruption of biological control, promotion of resistance in secondary pests, and intense selection for cross-resistance. Results from limited experimental work suggest that pesticide combinations do not consistently suppress resistance development. More thorough evaluation of tactics that seek to optimize benefits of more than one insecticide will require rigorous experiments with the particular pest and pesticide combinations. Because of the difficulty in generalizing results across systems and the potential negative effects of multiple insecticide use, emphasis on minimizing insecticide use is recommended.     

昆虫抗药性产生机制

杀虫剂是害虫防治的有效途径之一,但随着杀虫剂长期和广泛的使用,昆虫种群对各种杀虫剂的敏感性降低,产生了抗药性,如何克服昆虫的抗药性是害虫综合治理的重要问题。近年来,借助基因组测序和遗传操作技术的发展,对昆虫抗药性的研究已经深入到细胞水平和分子水平,取得诸多重要的突破,为害虫抗性的控制奠定了理论基础。本文从常见杀虫剂的历史沿革及作用机理切入,从靶标抗性、代谢抗性和穿透抗性3个方面阐述了杀虫剂抗性产生的机制:杀虫剂作用位点的突变降低了靶标与杀虫剂的亲和力,细胞色素P450酶系和谷胱甘肽转移酶系的激活增加了杀虫剂的降解,表皮结构成分的变化和ABC转运蛋白的增加有效阻挡了杀虫剂的渗入。利用基因操作手段或抑制剂,对上述3种抗性机制的关键步骤进行调控可能成为未来杀虫剂抗性控制的新策略。     

Insecticides suppress natural enemies and increase pest damage in cabbage

Intensive use of pesticides is common and increasing despite a growing and historically well documented awareness of the costs and hazards. The benefits from pesticides of increased yields from sufficient pest control may be outweighed by developed resistance in pests and killing of beneficial natural enemies. Other negative effects are human health problems and lower prices because of consumers' desire to buy organic products. Few studies have examined these trade-offs in the field. Here, we demonstrate that Nicaraguan cabbage (Brassica spp.) farmers may suffer economically by using insecticides as they get more damage by the main pest diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), at the same time as they spend economic resources on insecticides. Replicated similarly sized cabbage fields cultivated in a standardized manner were either treated with insecticides according common practice or not treated with insecticides over two seasons. Fields treated with insecticides suffered, compared with nontreated fields, equal or, at least in some periods of the seasons, higher diamondback moth pest attacks. These fields also had increased leaf damage on the harvested cabbage heads. Weight and size of the heads were not affected. The farmers received the same price on the local market irrespective of insecticide use. Rates of parasitized diamondback moth were consistently lower in the treated fields. Negative effects of using insecticides against diamondback moth were found for the density of parasitoids and generalist predatory wasps, and tended to affect spiders negatively. The observed increased leaf damages in insecticide-treated fields may be a combined consequence of insecticide resistance in the pest, and of lower predation and parasitization rates from naturally occurring predators that are suppressed by the insecticide applications. The results indicate biological control as a viable and economic alternative pest management strategy, something that may be particularly relevant for the production of cash crops in tropical countries where insecticide use is heavy and possibly increasing.     

History and Contemporary Perspectives of the Integrated Pest Management of Soybean in Brazil

The integrated pest management (IPM) of soybean developed and implemented in Brazil was one of the most successful programs of pest management in the world. Established during the 1970s, it showed a tremendous level of adoption by growers, decreasing the amount of insecticide use by over 50%. It included outstanding approaches of field scouting and decision making, considering the economic injury levels (EILs) for the major pests. Two main biological control programs were highly important to support the soybean IPM program in Brazil, i.e., the use of a NPVAg to control the major defoliator, the velvet bean caterpillar, Anticarsia gemmatalis Hübner, and the use of egg parasitoids against the seed-sucking stink bugs, in particular, the southern green stink bug, Nezara viridula (L.). These two biological control programs plus pests scouting, and the use of more selective insecticides considering the EILs supported the IPM program through the 1980s and 1990s. With the change in the landscape, with the adoption of the no-tillage cultivation system and the introduction of more intense multiple cropping, and with the lower input to divulge and adapt the IPM program to this new reality, the program started to decline during the years 2000s. Nowadays, soybean IPM is almost a forgotten control technology. In this mini-review article, suggestions are made to possibly revive and adapt the soybean IPM to contemporary time.     

Biological control and sustainable food production

The use of biological control for the management of pest insects pre-dates the modern pesticide era. The first major successes in biological control occurred with exotic pests controlled by natural enemy species collected from the country or area of origin of the pest (classical control). Augmentative control has been successfully applied against a range of open-field and greenhouse pests, and conservation biological control schemes have been developed with indigenous predators and parasitoids. The cost-benefit ratio for classical biological control is highly favourable (1:250) and for augmentative control is similar to that of insecticides (1:2-1:5), with much lower development costs. Over the past 120 years, more than 5000 introductions of approximately 2000 non-native control agents have been made against arthropod pests in 196 countries or islands with remarkably few environmental problems. Biological control is a key component of a 'systems approach' to integrated pest management, to counteract insecticide-resistant pests, withdrawal of chemicals and minimize the usage of pesticides. Current studies indicate that genetically modified insect-resistant Bt crops may have no adverse effects on the activity or function of predators or parasitoids used in biological control. The introduction of rational approaches for the environmental risk assessment of non-native control agents is an essential step in the wider application of biological control, but future success is strongly dependent on a greater level of investment in research and development by governments and related organizations that are committed to a reduced reliance on chemical control.     

Effects of induced plant resistance on soybean looper (Lepidoptera: Noctuidae) in soybean

Soybean looper, Chrysodeixis includens (Walker), is one of the most destructive pests of soybean in the southern U.S. Soybean looper defoliation exceeding 20% from R3 (pod initiation) to R5 (pod fill) can result in significant yield loss. In addition, soybean looper is highly resistant to many insecticides. An alternative to insecticide control is induced host plant resistance. In this study, a total of four experiments over 2 years were conducted in which three different elicitors of SAR (systemic acquired resistance), Actigard 50WG (acibenzolar-S-methyl), Regalia (extract of Reynoutria sachalinensis), and methyl jasmonate (MeJA), were applied to soybean at different plant stages to determine if these chemicals could induce plant resistance and lower soybean looper fitness. None of the elicitors of SAR significantly affected soybean looper mortality. However, Actigard 50WG, MeJA, and Regalia had adverse effects on developmental time, defoliation, and pupal weight of soybean looper. Induced effects by Regalia on soybean looper were very limited compared to Actigard 50WG and MeJA. A single application of MeJA reduced pupal weight by 6.8% and delayed larval development by 14.3%. Soybean seed production was not affected by application of elicitors. In conclusion, the results suggest that exogenous elicitors applied in the field can trigger plant resistance against herbivores and this low level of host plant resistance may effectively lessen pest pressure by favoring natural enemy population regulation without reducing seed production.     

Effects of insecticides on behavior of adult Bactericera cockerelli (Hemiptera: Triozidae) and transmission of Candidatus Liberibacter psyllaurous

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a serious pest of potatoes (Solanum tuberosum L.) that can cause yield loss by direct feeding on crop plants and by vectoring a bacterial pathogen, Candidatus Liberibacer psyllaurous. Current pest management practices rely on the use of insecticides to control the potato psyllid to lower disease incidences and increase yields. Although many studies have focused on the mortality that insecticides can cause on potato psyllid populations, little is known regarding the behavioral responses of the potato psyllid to insecticides or whether insecticides can decrease pathogen transmission. Thus, the objectives of this study were to determine the effects of insecticides on adult potato psyllid behaviors, the residual effects of insecticides on potato psyllid behaviors over time, and effects of these insecticides on Ca. L. psyllaurous transmission. Insecticides tested included imidacloprid, kaolin particle film, horticultural spray oil, abamectin, and pymetrozine. All insecticides significantly reduced probing durations and increased the amount of time adult psyllids spent off the leaflets, suggesting that these chemicals may be deterrents to feeding as well as repellents. Nonfeeding behaviors such as tasting, resting, and cleaning showed variable relationships with the different insecticide treatments over time. The insecticides imidacloprid and abamectin significantly lowered transmission of Ca. L. psyllaurous compared with untreated controls. The implications of our results for the selection of insecticides useful for an integrated pest management program for potato psyllid control are discussed.     

Spatial and Temporal Potato Intensification Drives Insecticide Resistance in the Specialist Herbivore,Leptinotarsa decemlineata

Landscape-scale intensification of individual crops and pesticide use that is associated with this intensification is an emerging, environmental problem that is expected to have unequal effects on pests with different lifecycles, host ranges, and dispersal abilities. We investigate if intensification of a single crop in an agroecosystem has a direct effect on insecticide resistance in a specialist insect herbivore. Using a major potato pest, Leptinotarsa decemlineata, we measured imidacloprid (neonicotinoid) resistance in populations across a spatiotemporal crop production gradient where potato production has increased in Michigan and Wisconsin, USA. We found that concurrent estimates of area and temporal frequency of potato production better described patterns of imidacloprid resistance among L. decemlineata populations than general measures of agricultural production (% cropland, landscape diversity). This study defines the effects individual crop rotation patterns can have on specialist herbivore insecticide resistance in an agroecosystem context, and how impacts of intensive production can be estimated with general estimates of insecticide use. Our results provide empirical evidence that variation in the intensity of neonicotinoid-treated potato in an agricultural landscape can have unequal impacts on L. decemlineata insecticide insensitivity, a process that can lead to resistance and locally intensive insecticide use. Our study provides a novel approach applicable in other agricultural systems to estimate impacts of crop rotation, increased pesticide dependence, insecticide resistance, and external costs of pest management practices on ecosystem health.     

Tandem use of selective insecticides and natural enemies for effective,reduced-risk pest management

Selective chemical insecticides have become the dominant approach for management of recalcitrant and resistant insect pests, and the prospects for use of these chemicals in combination with biocontrol agents are on the rise. These chemical compounds, when used in combination with an effective natural enemy, may provide more comprehensive prophylactic and remedial treatments in the context of an integrated pest management program (IPM) than either approach alone. Many of these compounds have promise for a diversity of applications, including sustainable agriculture, control of urban pests, and invasive species eradication. Unfortunately, there are only a limited number of studies in which the effect of these insecticides on natural enemies has been examined. In this article, we examine the risk of several classes of insecticidal compounds to non-target animals, particularly natural enemies and pollinators, and review the most promising compounds for combined deployment with biological agents.     

Population dynamics and "outbreaks" of diamondback moth (Lepidoptera: Plutellidae) in Guangdong province, China: climate or failure of management?

Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), became the major pest of Brassica vegetable production in Guangdong, a province in southeastern China, in the late 1980s and has continued to challenge growers, particularly during the spring and autumn. Control has relied on insecticides and, as has happened in other parts of the world, resistance to these has evolved and subsequent field control failures have occurred. We review and summarize the history of diamondback moth management in Guangdong. We show that the geographic distribution of the pest in China is well described by a simple climate niche model. Our model predicts the seasonal phenology and some of the variation in abundance among years in Guangdong. Discrepancies may reflect migration and insecticide use at a landscape level. The scale of the pest problem experienced varies with management practices. Local production breaks, and strict post harvest hygiene are associated with lower pest pressure on large-scale production units. As more and more insecticides become ineffective the need to implement an insecticide resistance management strategy, as well as basic integrated pest management practices, will become more pressing. The potential use and development of a better forecasting system for diamondback moth that will assist these developments is outlined.     

The evolution of insecticide resistance: Have the insects won?

While insecticides have greatly improved human health and agricultural production worldwide, their utility has been limited by the evolution of resistance in many major pests, including some that became pests only as a result of insecticide use. Insecticide resistance is both an interesting example of the adaptability of insect pests, and, in the design of resistance management programmes, a useful application of evolutionary biology. Pest susceptibility is a valuable natural resource that has been squandered; at the same time, it is becoming increasingly expensive to develop new insecticides. Pest control tactics should therefore take account of the possibility of resistance evolution. One of the best ways to retard resistance evolution is to use insecticides only when control by natural enemies fails to limit economic damage. This review summarizes the recent literature on insecticide resistance as an example of adaptation, and demonstrates how population genetics and ecology can be used to manage the resistance problem.     

Landscape simplification increases vineyard pest outbreaks and insecticide use

Diversifying agricultural landscapes may mitigate biodiversity declines and improve pest management. Yet landscapes are rarely managed to suppress pests, in part because researchers seldom measure key variables related to pest outbreaks and insecticides that drive management decisions. We used a 13‐year government database to analyse landscape effects on European grapevine moth (Lobesia botrana) outbreaks and insecticides across c. 400 Spanish vineyards. At harvest, we found pest outbreaks increased four‐fold in simplified, vineyard‐dominated landscapes compared to complex landscapes in which vineyards are surrounded by semi‐natural habitats. Similarly, insecticide applications doubled in vineyard‐dominated landscapes but declined in vineyards surrounded by shrubland. Importantly, pest population stochasticity would have masked these large effects if numbers of study sites and years were reduced to typical levels in landscape pest‐control studies. Our results suggest increasing landscape complexity may mitigate pest populations and insecticide applications. Habitat conservation represents an economically and environmentally sound approach for achieving sustainable grape production.     

An aphid-dip bioassay to evaluate susceptibility of soybean aphid (Hemiptera: Aphididae) to pyrethroid, organophosphate, and neonicotinoid insecticides

Since the discovery of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in North America in 2000, chemical control has been the most effective method to manage aphid outbreaks. Increased insecticide use in soybean raises the possibility of developing insecticide resistance in soybean aphid, and monitoring insecticide susceptibility is essential to maintain pesticide tools. We developed a simple and reliable aphid-dip bioassay by using a tea strainer that resulted in -90% survival in controls. Using this technique, we tested susceptibility of a greenhouse strain of soybean aphid that has never been exposed to insecticides, and field-collected aphid strains from two counties in Michigan. Aphid susceptibility was tested for five insecticides by dipping groups of five aphids in each insecticide dose for 10 s. After 48 h, aphids were classified as dead or alive, and counted. Aphids from all strains were highly susceptible to chlorpyrifos, lambda-cyhalothrin, esfenvalerate, and dimethoate, with LC50 and LC90 values well below the recommended application rates. However, aphids showed less susceptibility after 48 h to neonicotinoid imidacloprid, with higher LC90s and wider fiducial limits. This illustrated the potential limitation of using a 48-h assay to evaluate insecticides with longer-term, sublethal impacts. Nevertheless, this study made use of a simple aphid-dip method to test and compare insecticide susceptibility of soybean aphid. In the event of a field failure, the aphid populations involved can be tested in comparison to a susceptible greenhouse strain to determine the extent of resistance development.     

Role of biodiversity in integrated fruit production in eastern North American orchards

• 1 Diversifying agricultural ecosystems to enhance biological control is a promising way of promoting sustainable pest management.
• 2 In the present study, monoculture apple and peach with standard insecticide treatments were compared with three biodiverse treatments (polyculure, monoculture with companion plants and polyculture with companion plants) with reduced standard insecticide use.
• 3 Abundance of insect predators was increased by both the presence of companion plants and extrafloral nectar but parasitism of the leafroller Platynota idaeusalis was not affected.
• 4 There were no consistent effects of biodiversity treatment on either tree growth or fruit yield. Insect injury to Empire apple and peach fruit was not consistently affected by the biodiversity treatments. Granny Smith apples were harvested later than Empire and had more fruit injury in the biodiverse treatments than the standard insecticide control.
• 5 A reduction in pesticides with added biodiversity proved to be a viable alternative to standard chemical insecticide management for temperate tree fruit. Increases in the natural control of pests resulting from increased plant diversity has promise for reducing the reliance on chemical insecticides for pest suppression.

     

Optimum timing for integrated pest management: Modelling rates of pesticide application and natural enemy releases

Many factors including pest natural enemy ratios, starting densities, timings of natural enemy releases, dosages and timings of insecticide applications and instantaneous killing rates of pesticides on both pests and natural enemies can affect the success of IPM control programmes. To address how such factors influence successful pest control, hybrid impulsive pest-natural enemy models with different frequencies of pesticide sprays and natural enemy releases were proposed and analyzed. With releasing both more or less frequent than the sprays, a stability threshold condition for a pest eradication periodic solution is provided. Moreover, the effects of times of spraying pesticides (or releasing natural enemies) and control tactics on the threshold condition were investigated with regard to the extent of depression or resurgence resulting from pulses of pesticide applications. Multiple attractors from which the pest population oscillates with different amplitudes can coexist for a wide range of parameters and the switch-like transitions among these attractors showed that varying dosages and frequencies of insecticide applications and the numbers of natural enemies released are crucial. To see how the pesticide applications could be reduced, we developed a model involving periodic releases of natural enemies with chemical control applied only when the densities of the pest reached the given Economic Threshold. The results indicate that the pest outbreak period or frequency largely depends on the initial densities and the control tactics.     

DDT, pyrethrins, pyrethroids and insect sodium channels

The long term use of many insecticides is continually threatened by the ability of insects to evolve resistance mechanisms that render the chemicals ineffective. Such resistance poses a serious threat to insect pest control both in the UK and worldwide. Resistance may result from either an increase in the ability of the insect to detoxify the insecticide or by changes in the target protein with which the insecticide interacts. DDT, the pyrethrins and the synthetic pyrethroids (the latter currently accounting for around 17% of the world insecticide market), act on the voltage-gated sodium channel proteins found in insect nerve cell membranes. The correct functioning of these channels is essential for normal transmission of nerve impulses and this process is disrupted by binding of the insecticides, leading to paralysis and eventual death. Some insect pest populations have evolved modifications of the sodium channel protein which prevent the binding of the insecticide and result in the insect developing resistance. Here we review some of the work (done at Rothamsted Research and elsewhere) that has led to the identification of specific residues on the sodium channel that may constitute the DDT and pyrethroid binding sites.