Having an estimated production of 388 million tons in 2017(FAO 2019),potato is one of the world’s most important food crops,along with rice,wheat,and maize.Potato plants can adapt to different agricultural environments and are widely grown over many latitudes and elevations(Doucheset al.2004).In addition to its consumption in Europe,North America and countries of the former Soviet Union,potato is now also popularized in Africa and Asia,especially in the developing countries including China and India.Since 2015,China has been boosting potato production to become the fourth major crop produced in the country following rice,wheat and maize (Zhanget al.2017;Xuet al.2019).And developing potato as the staple food was also included by Ministry of Agriculture and Rural Affairs of China in its important agenda.Further improvement of potato production globally could promote the sustainable development of agriculture and safeguard world’s food security in the near future.

Insect pests are one of the major constraints to commercial production of potato in the world.For over 8 000 years since its domestication in the central Andes,the potato has been plagued by a number of serious insect pests (Radcliffe 1982).These include some of the most prolific and adaptable species known to human.If left uncontrolled,the insect pests can completely destroy the affected crops.With the rapid development of international trade,many insect herbivores of crops have spread across the continents along with agricultural products,and soon outbroke and became serious pests in their colonized areas(Carrilloet al.2019).To deal with the potato insect pest problems,currently several issues remain to be solved:(1)Know these insect pests.A deep decoding of the biology and ecology of the potato insect pests is the basis for developing counter-measures to them.(2)Know how the insects come and where they will go.Figuring out the spreading of the invasive insects of potato can help achieve a better prevention and slow down their damage risks.(3)Know their helpers during the harm to crops.The co-occurrence of insects and plant pathogens in potato fields requires the raveling of how they interacts.(4)Know the integrative management strategies.Insect management in commercial potato production is heavily reliant on synthetic backlash and causing environmental pollution,and thus new strategies are needed to achieve a more ecological control of these pests.

As guest editors,we are pleased to present 12 papers about the biology,ecology and management of major insect pests damaging on the potato crop in this special focus of theJournalofIntegrativeAgriculture.We hope to improve our understanding of insect pests of potato and provide guidance for countries facing the IPM of those pests worldwide.The 12 papers are organized into the following four sections.

Section 1:Decoding potato insect pests

Insect pests are under constant evolution,in the way of adaptation and phenotypic plasticity,to the changing environments (Sgròet al.2016).Climate variation have increased the possibility of changes in insect pests’ biological and ecological patterns (Andrewet al.2013).Decoding the insect pests is thus a continuous task for entomologist under the changing scenarios.The potato tuber mothPhthorimaea operculellais one of the main pests affecting potatoes around the world (Yuanet al.2018).Since the first report ofP.operculellaand its damage on potato in South America in the early 1900s (Graft 1917),more than 700 articles have been published on diverse aspects of this insect herbivore.Rondonet al.(2020)provided an exhaustive update on the current knowledge available forP.operculella,through extracting the key information including the development,the host plant,the geographical distributions,the populations dynamics,and the management of this insect.Apparently,temperature is one of the most important factors affecting these traits (Régnièreet al.2012).It remains to see how climate change may affect the distribution and performance ofP.operculellain future.

Rondonet al.(2020)also pointed out the gap in knowledge regarding the close evolutionary link between the potatoes andP.operculella.Understanding the insectplant fundamental relationship is crucial for developing sustainable pest control strategies (Pickettet al.1997).Host plant resistance traits,which enables plant to avoid or tolerate the insects,can help reduce or stopP.operculellafrom damage (Horganet al.2013).Liet al.(2020)analyzed the olfactory responses ofP.operculellato the volatile organic compounds from tobacco plant.After screening the volatiles by gas chromatography-electroantennogram and electroantennogram recording,they found thatcis-3-hexen-1-ol,nonanal and decanal showed a significant attractant effect on the adult moths,while octanal exhibited a repellent effect on males.Moreover,four chemicals nonanal,decanal,decane and methyl hexadecanoate could promote the egg laying,while octanal and 2,6-bis(1,1-dimethylenthyl)-4-methyl phenol could inhibit the oviposition.These chemicals may serve as potential deterrents or attractants forP.operculella.The recent genome resequencing of tuber-bearingSolanumalso provided a potential path for uncovering the complex evolutionary history of cultivated potato (Hardiganet al.2017),and potential targets of domestication toP.operculellain the potato remain to be identified.

Compared to theP.operculella,the psyllidBactericera cockerelliis a more recently spread potato insect pest.Vereijssen (2020)summarized the current information on theB.cockerelliand the plant pathogenic bacteriumCandidatusthey transmit,with a special focus on the current situation of these two pests in New Zealand.The successful establishment ofB.cockerelliin New Zealand is a very recent incidence happened in the past two decades (Teulonet al.2009).Due to its serious damage to the solanaceous crop industry in New Zealand,the findings summarized by Vereijssen (2020)in this special focus may offer valuable References for the prevention of this pest in newly invaded areas globally in the near future.

Section 2:Invasive insect pests of potato:global perspectives

The promotion of solanaceous crop planting offered an unprecedented chance for potato insect pests to get in touch with their food source and find suitable eco-niches globally.In addition to the establishment of insect pest populations in un-invaded areas caused by global climate change,the rapid development of international trade also promoted the spread of many insect pests of solanaceous plants across the continents.Bactericera cockerelliand the Colorado potato beetleLeptinotarsadecemlineataare the two most dangerous invasive pests for potato and other solanaceous crops.

Since the invading ofB.cockerellito New Zealand,Asia-Pacific countries have to face an unprecedented risk of being invaded by this pest.In fact,B.cockerelliinvaded Australia soon after establishing its population in New Zealand (Walkeret al.2015).Olaniyanet al.(2020)provided a useful review onB.cockerelliwhich not only summarized the biological and ecological characters and the management strategies of this pest in a very detail way,but also discussed the integrative manners for preventing and assessing the risk of potential establishment of this dangerous pest in China and other countries.This review may provide a timely guidance for the scientists in those countries to prevent the invading of this dangerous pest in the near future.

The identification ofL.decemlineatain Northeast China indicates its successful spreading to Asian countries from Europe,which might be due to the lack of nature barrier to prevent their spreading.Understanding the invading path is the first step forL.decemlineatamanagement.Yanget al.(2020)used nine polymorphic microsatellite loci to elucidate the genetic diversity,genetic structure and gene flow amongL.decemlineatapopulations across Northwest and Northeast China.They offered evidences that multiple introductions of this invasive pest may occur in Northeast China.Since the distribution ofL.decemlineatais limited to specific regions in North China,the management of this pest in invasive frontier areas is thus important for slowing down its spreading and damage.Wanget al.(2020)summarized the management methods that are used in areas at the frontier of theL.decemlineata,and offered frameworks for the further prevention and control of the spread ofL.decemlineata.

Section 3:The interaction between potato aphids and virus

Aphids are the most widely distributed pests for the cultivated potato and aphid-transmitted potato viruses have been emerging in the potato fields around the world as a very serious problem in potato production (Radcliffeet al.2002).The most serious virus disease for potato production is potato virus Y (PVY),which is transmitted in a non-persistent manner by aphids (Scholthofet al.2011).Numerous studies have uncovered the biological characters of PVY,while the knowledge of PVY spread in the potato field remains rare.Galimbertiet al.(2020)developed a spatially-explicit model to simulate the PVY spread in the field and used it to investigate possible effects of transmission efficiency,initial inoculum levels,vector behavior,vector abundance,and timing of peak vector activity on PVY incidence at the end of a simulated growing season.This simulation mainly focuses on the intrinsic factors of the virus vector.It may offer valuable information for the pest control in the real field.

Xu and Stewart (2020)presented a more integrative review on the biological characteristics of aphids,their transmitted potato viruses,and the interaction of these two biological stress factors to potato crop in the context of variable environments.The concurrence of aphids and their transmitted potato viruses in the field likely introduces a more complicated stress response in plants in comparison to the single stress caused by one of them alone.Thus,a comprehensive view of the interactions among plants,viruses,virus vectors and the environment is necessary for elucidating the pest problems in the real nature.

Section 4:Integrative management strategies for potato insect pests

Insecticides are most widely used for the control of potato insect pests.The intensive use of pesticides not only has negative impacts on the environment,food safety and human health,but also causes the development of pesticide resistance in insects (Doğramacıet al.2008).Alternative strategies are thus required for the management of insect pests in potato.As a leaf miner or tuber miner,P.operculellacannot touch many insecticides directly.The entomopathogenic nematodeSteinememacarpocapsaehas been proved to be effective as the biological control agent against many insect pests (Shapiro-Ilanet al.2015).Yanet al.(2020)studied the pathogenic effects ofS.carpocapsaeonP.operculella.They determined the median lethal concentration ofS.carpocapsaeon the larvae and found that the fourth instar larvae are most susceptible for all observed stages.This study may promote the application of this entomopathogen in the biological control ofP.operculella.

Beside the entomopathogenic nematode,there are many different natural enemies forP.operculellain the field.Zhenget al.(2020)tested theP.operculellainfestation in potato/maize intercropping system.Interestingly,they found that intercropping potato with the non-host plant maize could reduce theP.operculellapopulation and its damage to the potato plants.This reduction is likely due to the enhanced number of parasitoids and the level of parasitism in the intercrop fields.It would be interesting to see how intercropping enhance the natural enemy population in the following studies.

In addition to the biological strategies,chemicals which can promote the physiology of crops are also promising agents not only for the plant growth but also for the insect resistance and tolerance.Mulugetaet al.(2020)introduced the application of botanicals and plant strengtheners for potato and tomato cultivation in Africa.Botanicals are defined as plant extracts,volatiles and natural oils which exhibit pest/pathogen control activities;while plant strengtheners are substances or micro-organisms which enhance nutrient uptake,nutrient efficiency,tolerance to abiotic stress,and crop quality,and they normally do not have direct action against insect pests and pathogens.This review may promote the use of botanicals and plant strengtheners in sustainable African agriculture.

RNA interference (RNAi)has been widely used in the study of gene functions inL.decemlineata.It is recently recognized as a safe,efficient,and eco-friendly potential strategy for the management of insect pests.Maet al.(2020)summarized the recent advances in the study of RNAi target genes,the RNAi delivery system,and factors affecting RNAi efficiency inL.decemlineata.With the development of double-stranded RNA (dsRNA)vast synthetic technics and chloroplast-transformation based high-efficient dsRNA delivery system,the RNAi-based control ofL.decemlineatais likely to be popularized in the near future.

The outbreak of potato herbivores has received less attentions worldwide than the outbreak of pathogen diseases.The word ‘Pests’ for potato production was commonly endowed with ‘Pathogens’ in the past.On the other hand,the rapid spreading and frequent outbreak of many serious potato insect pests is now recognized in many countries.We hope our readers will find the information presented in this special focus useful.In addition to providing a global outlook for potato insect pests,our special focus may also open a timely window for the study of potato insect pests in the new era by offering important scientific questions,and for the management of them by sharing some recent technical advances of integrative pest control.We thank the Editorial Department and Editor-in-Chief of theJournalofIntegrative Agriculturefor accepting our proposal to organize a special focus and their collaboration in inviting the peer reviewers and eventually in assembling the accepted manuscripts into this piece of work.We thank the National Key Research and Development Program of China (2018YFD0200802)and the Key R&D Plan of Zhejiang Province,China (2019C04007)and the Fundamental Research Funds for the Central Universities,China (2019FZA6013)for support in potato insect pest researches held in Hangzhou and the publication of this special focus.

GAO Yu-lin

Guest Editor

State Key Laboratory for Biology of Plant Diseases and Insect Pests,

Institute of Plant Protection,Chinese Academy of Agricultural Sciences,

Beijing 100193,P.R.China

E-mail:gaoyulin@caas.cn

ZHOU Wen-wu

Guest Editor

Key Laboratory of Molecular Biology of Crop

Pathogens and Insects,Ministry of Agriculture/Key

Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province/State Key Laboratory of Rice Biology Institute of Insect Sciences,Zhejiang University,Hangzhou 310058,P.R.China

E-mail:wenwuzhou@zju.edu.cn