Larval diet affects development and reproduction of East Asian strain of the fall armyworm,Spodoptera frugiperda

In December 11,2018,the fall armyworm(FAW),Spodoptera frugiperda invaded China and has since impacted local maize,sorghum and other crops.Here,we draw on laboratory experiments to show how different host crops(i.e.,maize,sorghum,wheat and rice)and artificial diet affect larval growth and adult reproduction of one local FAW strain.Larval diet affected development duration,pupation rate,survival and emergence rate of pupae,and S.frugiperda adult fecundity.FAW attained the slowest larval development(19.4 days)on sorghum and the fastest(14.1 days)on artificial diet,with larvae attaining 99.6%survival on the latter food item.On rice,FAW larvae attained survival rate of 0.4%and were unable to pupate successfully.Pupation rate and pupal survival varied substantially between artificial diet and live plantlets at different phenological stages.Pupal weight was the highest(0.26 g)on artificial diet and the lowest(0.14 g)on sorghum,while FAW females reached the highest fecundity(699.7 eggs/female)on 2-leaf stage maize.Egg hatching rate equaled 93.6%on 4-or 5-leaf stage maize and 36.6%on artificial diet.FAW intrinsic rate of natural increase and the finite rate of increase varied between larval diets,reflecting how young maize leaves are the most suitable diet.Our findings can help to refine laboratory rearing protocols,devise population forecasting models or guide the deployment of‘area-wide’integrated pest management(IPM)modules in FAW-invaded areas of China and other Asian countries.

Laboratory-based flight performance of the fall armyworm,Spodoptera frugiperda

In late 2018,the fall armyworm(FAW)Spodoptera frugiperda Smith(Lepidoptera:Noctuidae)made its arrival in China and its populations have since proliferated across most of eastern Asia.While S.frugiperda exhibits a considerable dispersal capacity and engages in long-distance migration,there’s only scant information on the species’flight capability.Here,we empirically assessed S.frugiperda flight activity under varying climatic conditions using a flight mill.More specifically,under laboratory conditions,FAW exhibited superior flight performance at 20-25℃ and 60-90%relative humidity(RH).When quantifying flight performance over five consecutive nights(i.e.,10 h/night),all flight parameters initially increased and then gradually dropped and FAW adults attained a total flight distance,duration and velocity equal to 63.73 km(48.42-94.12 km)(median,quartile range),24.12 h(20.87-27.73 h)and 2.73 km h^(-1)(2.13-3.33 km h^(-1)),respectively.Our work constitutes a first comprehensive assessment of S.frugiperda flight performance and provides baseline information for future efforts to forecast spatiotemporal changes in its geographical distribution,movement patterns and invasion trajectories.Such can ultimately permit a timely and targeted deployment of area-wide pest management measures against this newly-invasive pest in China and across eastern Asia.

Population life tables for the invasive fall armyworm,Spodoptera frugiperda fed on major oil crops planted in China

The fall armyworm(FAW),Spodoptera frugiperda,is a newly invasive,widespread agricultural pest in China.Understanding the suitability of the main field crops in Chinese agricultural system as host for this polyphagous herbivore is especially important for making control strategy.Here,after FAWs were fed three important oil-bearing crops(oilseed rape,soybean and sunflower)planted in China and resultant population parameters were compared using the age-stage,two-sex life table method,survival of larvae on soybean was significantly lower than that on oilseed rape and sunflower.Developmental duration of larvae on soybean was also the longest(23.3 days).The highest pupation rate was recorded on sunflower.The highest pupal mass(0.19 g)was attained on oilseed rape,significantly higher than on the other host plants;the lowest mass was on soybean(0.15 g).On soybean,oilseed rape and sunflower,respectively,the average generation period was 42.21,39.10 and 40.44 d;the intrinsic rate of increase(r)was 0.0844,0.1041 and 0.1134;the finite rate of increase(λ)was 1.0881,1.1098 and 1.1202.While the most suitable host plant overall was sunflower,S.frugiperda completed development and increased its population on all three host plants.Thus,soybean,oilseed rape and sunflower were all suitable for FAW,and population monitoring and management of FAW in these crops should be increased.

Flight activity promotes reproductive processes in the fall armyworm,Spodoptera frugiperda

The fall armyworm(FAW),Spodoptera frugiperda(Lepidoptera:Noctuidae),has invaded many countries in Africa and Asia since 2016,posing a major threat to world food security.Long-distance migration and strong reproductive ability form the biological basis of its rapid population expansion,but the relationship between the flight and reproduction of FAW has not been studied in depth.Here,an empirical assessment of this relationship in an invasive FAW population in China found that 1-3-day-old adults which had undergone 10-h tethered flights had a significantly shorter pre-oviposition period and greater oviposition synchronization,but did not show any differences in fecundity,oviposition period,mating percentage or other reproductive variables.Further studies on moths after 1.25-15-h tethered flights indicated that the reproductive process of adults could be fully triggered by flight activity longer than 2.5 h.Dissection of the reproductive organs also showed that tethered flight promoted ovarian and testicular development of FAW.These results show that appropriate moth flight activity significantly speeds up the reproductive process of FAW,which increases our knowledge on its migratory biology in relation to regional outbreaks.

Adult nutrition affects reproduction and flight performance of the invasive fall armyworm,Spodoptera frugiperda in China

Floral resources,such as carbohydrate-rich nectar or pollen,can bolster fitness and raise reproductive output of adult lepidopterans.Here,we used laboratory experiments to assess how those plant-derived foods impact adult fecundity,reproductive physiology and flight performance of an invasive strain of the fall armyworm,Spodoptera frugiperda(FAW;Lepidoptera:Noctuidae)in China.More specifically,supplementary feeding on bee pollen and honey enhanced FAW flight duration,testis size,ovarian development,longevity and adult fecundity.FAW adults attained the longest pre-oviposition(10.8 days)and oviposition period(6.8 days)and longevity(19.2 days)on 5%acacia honey.Upon access to 2.5%acacia honey and 2.5‰pine pollen,S.frugiperda attained the highest mating rate(79.7%),fecundity(644.9 eggs/female)and egg hatching rate(82.3%).Feeding on honey further delayed decay of male testes,while ovarian development was enhanced when female moths were allowed access to 2.5%honey and 2.5‰pine pollen.Upon feeding on 5%honey solution,S.frugiperda engaged in flight over the longest duration(9.5 h),distance(29.9 km)and speed(3.1 km h-1).Honey had a comparatively greater effect on the above parameters than pollen.Our findings help decipher FAW invasion patterns and population dynamics,facilitate the development of nutritional attractants,and contribute to integrated pest management of this newly-invasive pest in eastern Asia.

Searchlight trapping reveals seasonal cross-ocean migration of fall armyworm over the South China Sea

The fall armyworm(FAW),Spodoptera frugiperda,is a migratory noctuid pest that has recently invaded eastern Asia.From 2017 up till 2020,searchlight trapping was used to assess the extent of FAW migration across the South China Sea.Molecular and morphology-based identification confirmed that FAW made its first appearance on Yongxing Island on 11 April 2019,with most trapped individuals belonging to the S.frugiperda"corn-strain".Carbon isotope analysis further showed that FAW moths originated from C4 host plants,while trajectory analyses revealed that migratory S.frugiperda adults are able to cross the South China Sea and enter China's Mainland.This long-distance migration process plausibly results in frequent genetic mixing between domestic FAW populations and those of neighboring Southeast Asian countries.Overall,this work provides unique insights into FAW migration across eastern Asia and ultimately can help advance pest forecasting,risk assessment and area-wide pest management.

Two-way predation between immature stages of the hoverfly Eupeodes corollae and the invasive fall armyworm(Spodoptera frugiperda J.E.Smith)

Since its 2018 invasion of eastern Asia,the fall armyworm Spodoptera frugiperda(Lepidoptera:Noctuidae)has become a key pest in local maize production.Though pesticides have been widely used to mitigate the initial S.frugiperda attack,biological control is receiving ample attention as a desirable,environmentally-sound alternative to chemical control.Hoverflies(Diptera:Syrphidae)are abundant natural enemies in Chinese maize fields and have been observed to consume S.frugiperda larvae.In this study,we use laboratory assays to study the two-way interaction between immature stages of S.frugiperda and the endemic syrphid Eupeodes corollae.To mimic natural conditions,assays were performed in the presence of fresh maize leaves.Those 2 nd or 3 rd instar larvae of E.corollae preyed on 1 st and 2 nd instar S.frugiperda larvae with a Holling type III response,consuming a respective theoretical maximum of 43.48 and 83.33 larvae over a 24-h period.Conversely,once S.frugiperda larvae reached 3 rd instar,they exhibited aggressive behavior and equally preyed on syrphid larvae with a Holling type III response.Those 5 th and 6 th instar larvae of S.frugiperda consumed a respective 16.39-19.23,6.02-19.61 and 6.76-8.26 of 1 st,2 nd and 3 rd instar E.corollae larvae per day.Though our results await field-level validation,S.frugiperda agonistic(i.e.,defensive)and consumptive behavior towards resident natural enemies such as E.corollae possibly degrades biotic resistance and raises its invasion potential.Our findings shine new light on the interaction between lepidopteran herbivores and their natural enemies,and can help advance the development of conservation biological control and other integrated pest management(IPM)strategies against S.frugiperda in China and abroad.

The Role of Natural and Human-Mediated Pathways for Invasive Agricultural Pests:A Historical Analysis of Cases from Brazil

Information about the geographic distribution of agricultural pests is the basis for all pest-related agricultural and environmental protection policies. However, often the pest’s records are incomplete and uncertain. Even with limitations, the pest records are needed for any country to organize a system for agriculture protection and to mobilize surveillance efforts. The first point is to identify the imminence of biological invasions, which can be accomplished through the collection of data on pest distribution. The basic information to evaluate the predictability of an invasion is geographic distribution and the identification of pathway types associated with the potential invader. Thus, the level of the risk of introduction is assessed more objectively. In this article, cases of introduction of pests were analyzed from published reports in Brazil in terms of their geographic distribution at the time of their introduction. Taking into consideration the country’s extensive terrestrial borders, this study attempts to elucidate the role played by different pathways in each bioinvasion. This analysis recognized the limitations of the historical method and underlying uncertainties of each invasion event. Human-mediated pathways were the main source of agricultural pest invasions in Brazil and the country was more a disperser than a receptor of exotic agricultural pests and diseases in South America. A new geographical hotspot (Northern South America and Caribbean Region) for possible invasions was identified.

Multiple mechanisms in woodland plant species invasion

Aims A plethora of theories explain species invasion,yet when tested in isolation,support or falsification becomes contingent on study species,system and approach.Our objective was to examine com-munity-level species invasion as a function of multiple competing hypotheses.Methods We used data from>3500 woodland plant species in 2750 plots in 49 national parks in eastern US deciduous forests to test multiple competing theories of species invasion:competition,empty niche,propagule pressure and latitude matching.We also tested interac-tions with residence time to account for non-native species naturali-zation and spread since arrival.Important Findings The non-native herbs generally thrived at latitudes similar to those from which they originated,but not necessarily where they were originally introduced to the eastern US.Overall,we found that each hypothesis explained at least some aspect of woodland plant species invasion,but examining them simultaneously allowed assessment of their relative strengths and interactions.Our results suggested that residence time is a strong predictor of non-native woodland plant success,particularly as it interacts with other mechanisms of inva-sion,such as competition(abundance of native woodland plants),climate matching(similar invaded latitude as home range),prop-agule pressure(distance to putative seed sources)and empty niche(relatedness to native plants).We found that initial barriers,such as distance from propagule source or suboptimal habitat,were over-come,as was resistance from native relatives.However,the biggest challenge for the non-native woodland plants appeared to be time,as they declined after~1 to 2 centuries.

Evolutionary ecology of microsporidia associated with the invasive ladybird Harmonia axyridis

Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity and the economy. It is unclear why some species can become successful invaders, whereas most （even if closely related） remain noninvasive. We previously proposed a hypothesis that parasites associated with invading species can promote their invasive success if they are harmless toward the invaders but harmful to their competitors and/or predators in the newly colonized habitat. Here we discuss whether microsporidia that have recently been discovered in the invasive ladybird Harmonia axyridis contribute to its invasive success. We show that all H. axyridis beetles sourced from diverse collection sites all over the world carry abundant microsporidia. This suggests that both native and invasive H. axyridis populations are associated with these tolerated parasites, which were likely to have existed in native populations before expansion rather than being acquired in newly colonized areas. We describe the pathogenesis of the microsporidia during different developmental stages of H. axyridis and we address the possibility that the predation of its infected eggs and larvae by competing native ladybird species may lead to their infection and ultimately to their decline. Finally, we discuss our initial hypothesis： microsporidia that are tolerated by an invasive vector insect can be active against susceptible native competitors and/or predator species.