Massive seasonal high-altitude migrations of nocturnal insects above the agricultural plains of East China

Protected area coverage of the full annual cycle of migratory butterflies

Effective conservation of migratory species relies on habitat protection throughout their annual cycle. Although protected areas (PAs) play a central role in conservation, their effectiveness at conserving habitats across the annual cycle of migratory species has rarely been assessed. We developed seasonal ecological niche models for 418 migratory butterfly species across their global distribution to assess whether they were adequately represented in the PAs across their full annual cycle. PA coverage was inadequate in at least one season for 84% of migratory butterflies, adequate for only 17% of species in one season, and inadequate for 45% of species in all seasons. There was marked geographic variation in PA coverage: 77% of species met representation targets in Sri Lanka, for example, but only 32% met targets in Italy. Our results suggest that coordinated efforts across multiple countries will be needed to develop international networks of PAs that cover the full annual cycle of migratory insects and that conservation measures, in addition to the establishment and maintenance of PAs, are likely to be needed to effectively conserve these species.

Transboundary Dispersal Dynamics of Ceracris kiangsu: From Source Regions to Migration Corridors

Yunnan is located on the southwest border of China, with a complex geographical environment and rich biodiversity, which is the first stop for many migratory pests to enter China. In recent years, Ceracris kiangsu has migrated into China through the China-Laos border line. The migratory C. kiangsu has shown typical characteristics of migratory locusts, which has seriously jeopardized the ecological security, biosecurity and food security of China. In order to prevent and control C. kiangsu from the source as soon as possible, this study used hotspot analysis and trajectory analysis to clarify the migration dynamics, source regions and migration corridors of C. kiangsu. The results showed that the migratory C. kiangsu was mainly distributed in the towns of Jiangcheng County, and the source regions were concentrated in Phongsaly, Laos. There are three cross-border migration corridors of C. kiangsu, among which the Laos-Niuluohe border migration corridor running through the entire migration cycle is the most important corridor. The study answered three key questions about the prevention and control of C. kiangsu. Ascertaining when C. kiangsu arrived at Yunnan, where it came from, and where the population then went will greatly improve the efficiency of the prevention and control of C. kiangsu as well as provide a theoretical basis for subsequent monitoring and early warning.

Characteristics and seasonal variation of fall armyworm migratory behavior in their year-round breeding areas in South China

BACKGROUND

The occurrence of migratory takeoff behavior is the essential first step for long-distance migration of insects. However, its characteristics, frequency of occurrence, and the identity of environmental and physiological factors influencing this process remain largely unknown.

RESULTS

We investigate the global pest fall armyworm (FAW, Spodoptera frugiperda) as an exemplar species to investigate the behavioral traits associated with migratory takeoff of nocturnally migrating moths in year-round breeding areas. Our studies of FAW were carried out in Yunnan (2020-2022) and Hainan (2023) provinces of South China. Most migratory FAW moths were observed to takeoff at the age of Day (D)1-3, with the highest migratory proportion on D2, whereas mating behavior mostly happened during the first half night on D1. Typically, the migratory individuals took off within 40 min after sunset when the illumination fell below 2.7 lx, reaching its peak within 15 min. The optimal conditions for their takeoff are warm and dry weather with gentle winds. Yunnan and Hainan field populations showed a similar seasonal pattern in their migratory proportion, with the highest proportion in spring, and then decreasing as the seasons progress. Additionally, FAW moths emerging from caterpillars fed on maize plants at V14-R1 stages showed a higher migratory proportion than those from larvae fed on maize plants at other growth stages. Compared with nonmigratory individuals, migratory ones had slightly longer forewings (marginally significant) and flew faster, with higher wingbeat frequency, but other morphological characteristics and flight parameters were similar.

CONCLUSION

The study of FAW moths in Yunnan and Hainan from 2020 to 2023 found that migratory moths take off under specific conditions and show a seasonal pattern, with those from certain maize stages having higher migratory proportion, longer forewings and faster flight. These findings advance our understanding of the migratory takeoff behavior of FAW and, thus, provide a basis for the accurate prediction and management of the migratory dynamics. © 2025 Society of Chemical Industry.

First high-resolution vertical-looking radar for long-term automatic observation of high-flying insects in Asia

BACKGROUND

The increasing occurrence of migrant insect pests poses a serious threat to the sustainability of agriculture and to food security. Continuous monitoring of high-flying insects plays a crucial role in developing effective pest management strategies and implementing successful control measures.

RESULTS

The present study established vertical-looking radar (VLR) monitoring of insects in Henan Province, China, with a unit incorporating up-to-date high frequency digitization technology and rapid target-finding procedures. This radar produced detailed information on target identification (size, shape, wingbeat frequency) and flight behavior (flight time, height, track speed, track direction, body alignment, and climb rate) for insects flying at altitudes of from 70 m to 1810 m above the ground. The lowest detection range for insects is lower than that (150 m) normal in previous VLR systems. The VLR-inferred tracking of small insects could also provide accurate estimates of wind velocity.

CONCLUSION

The VLR achieved long-term automatic observation of high-flying insects for the first time in Asia. This provided a unique tool for automatic long-term monitoring of high-flying insects to help to answer some basic scientific questions, such as the impacts of climate change on insect populations, and provide surveillance information for insect pest control in this region. The three-step target identification method and the performance calibration protocol for the VLR established in this study are both straightforward and reliable. These methods can be easily implemented and adapted for use in other settings, making them valuable tools for enhancing radar-based entomological research and monitoring. © 2025 Society of Chemical Industry.

Climate change is leading to an ecological trap in a migratory insect

Many insect migrants rely on favorable seasonal winds to carry out long-range latitudinal migrations. In East China, the annual advance and retreat of the East Asian summer monsoon produces ideal conditions for seasonal range expansion and contraction of many migratory crop pests. However, climate-induced changes in the strength, timing, and location of the monsoon are impacting wind systems which may, in turn, affect migration patterns. We investigated these questions in the rice leafroller (RLR) moth, a severe pest of rice that annually invades the Lower Yangtze River Valley (LYRV) of China from winter-breeding areas further south. Using a 24-y dataset of RLR population dynamics from 31 monitoring stations across Southeast China, we investigated the impact of changes in monsoon wind regimes on fall migration patterns of the pest. Historically, RLR emigrated from the LYRV to South China on the favorably directed winds produced by the retreat of the monsoon at the end of the outbreak season (from mid-August onward). We show that in the recent 12-y period, prevailing late-season winds remain northward for longer than previously, preventing locally produced moths from emigrating southward. Additionally, winds now facilitate mass late-season immigrations into the LYRV, creating an ecological trap, as immigrants do not have time to produce another generation. As a consequence of the changing wind patterns, pest pressure is declining, and climate-induced changes to the East Asian summer monsoon result in seasonal migration becoming a riskier strategy. Such changes in insect migration patterns have severe implications for the population dynamics of windborne migrants, ecosystem functioning, and pest management strategies.

The East Asian Insect Flyway: Geographical and Climatic Factors Driving Migration Among Diverse Crop Pests

The East Asian Insect Flyway is a globally important migration route stretching from the Indochina Peninsula and the Philippines through East China to Northeast China and northern Japan, although most migrants utilize only part of the flyway. In this review, we focus on long-range windborne migrations of lepidopteran and planthopper pests. We outline the environment in which migrations occur, with emphasis on the seasonal atmospheric circulations that influence the transporting wind systems. Northward movement in spring is facilitated by favorable prevailing winds, allowing migrants to colonize vast areas of East Asia. Migrants may be subject to contemporary natural selection for long flights as succeeding generations progressively advance northward. Overshooting into far northern areas from which there is little chance of return seems common in planthoppers. Moths are less profligate and have evolved complex flight behaviors that can facilitate southward transport in autumn, although timely spells of favorable winds may not occur in some years.

The use of visual and olfactory cues by adult Spodoptera frugiperda (Lepidoptera: Noctuidae) while foraging

The fall armyworm Spodoptera frugiperda (J.E. Smith; Lepidoptera: Noctuidae) is a notorious invasive insect pest. It is very important to understand the foraging behavior of this pest to develop more effective lures to monitor the immigration of this pest. In this study, the use of visual and olfactory cues in the foraging behavior of S. frugiperda was investigated through an attraction experiment in which color (produced from 8 different colored artificial flowers), odor (produced from honey water), and odorous color (produced from artificial flowers supplemented with honey water) were used. When we used 8 different colors to elicit adult responses, S. frugiperda showed a significant color preference despite limited activity (i.e., the total number of visits to the attractant), with black being the most preferred color, followed by orange preferred by both sexes and blue and green preferred only by females. When honey water was used as an attractant, S. frugiperda had relatively greater odor activity than color activity. When we sprayed the artificial flowers with honey, S. frugiperda showed even greater activity in terms of odor color than in terms of color or odor. Compared with male S. frugiperda, female adult S. frugiperda presented greater activity in response to all types of attractants. These findings suggest that S. frugiperda adults rely primarily on olfaction for foraging, with vision as a secondary sense, and that the combined use of olfactory and visual cues increases foraging efficiency. These results provide reference data for designing trapping strategies to monitor and control S. frugiperda.

Pathogens spread by high-altitude windborne mosquitoes

Recent studies have revealed that many mosquito species regularly engage in high-altitude windborne migration, but its epidemiological significance was debated. The hypothesis that high-altitude mosquitoes spread pathogens over large distances has not been directly tested. Here, we report for the first time that high-altitude windborne mosquitoes are commonly infected with arboviruses, protozoans, and helminths affecting vertebrates and humans, and provide the first description of this pathogen-vector aerial network. A total of 1,017 female mosquitoes (81.4%, N=1,249) intercepted on nets suspended from helium balloons at altitudes of 120-290 m above ground over Mali and Ghana were screened for infection with arboviruses, plasmodia, and filariae, using pan-genus qPCR analyses followed by sequencing of positive samples. The mosquito fauna collected at altitude comprised 61 species, across 9 genera, dominated by Culex, Aedes, and Anopheles. Infection and infectiousness rates of high-altitude migrant mosquitoes were 7.2% and 4.4% with plasmodia, 1.6% and 0.6% with filariae, 3.5% and 1.1% with flaviviruses, respectively. Nineteen mosquito-borne pathogens were identified, including three arboviruses: dengue, West Nile and M'Poko viruses, 13 putative plasmodia species including Plasmodium matutinum and P. relictum, three filariids, including Pelecitus spp., 27 insect-specific viruses and 5 non-mosquito-borne pathogens (e.g., Trypanosoma theileri). Confirmed head-thorax (disseminated) infections of multiple pathogens in multiple mosquito species, eg., Culex perexiguus, Coquilletidia metallica, Mansonia uniformis, and Anopheles squamosus provides evidence that pathogens carried by high-altitude windborne mosquitoes are infectious and likely capable of infecting naïve hosts far from their starting location. This traffic of sylvatic pathogens may be key to their maintenance among foci as well as initiating outbreaks away from them.

Seasonal Migratory Activity of the Beet Armyworm Spodoptera exigua (Hübner) in the Tropical Area of China

The beet armyworm Spodoptera exigua (Hübner), a global pest, feeds on and affects a wide range of crops. Its long-distance migration with the East Asian monsoon frequently causes large-scale outbreaks in East and Southeast Asia. This pest mainly breeds in tropical regions in the winter season every year; however, few studies have investigated associations with its population movements in this region. From 2017 to 2023, we monitored its population dynamics in a tropical site, located in Hainan Province of China, using a searchlight trap. Dissection of the ovaries of female S. exigua moths captured from the air revealed that most of them were reproductively mature and could be classified as a transit migratory population. Migration occurred most often in summer and least often in winter, with an increasing trend over the years. According to a trajectory model analysis based on the Weather Research and Forecasting (WRF) model, S. exigua migrated from Hainan Island to mainland China in the spring, primarily moved from the areas of Southeast Asia to Hainan and mainland China during the summer, and returned from China to Southeast Asia in the autumn and winter. Overall, our research defines the movement paths of S. exigua in the tropical area of China, establishing a theoretical foundation for its regional monitoring, early warning, and management in China and Southeast Asian countries.

Interactions between migration and immunity among oriental armyworm populations infected with the insect pathogenic fungus, Beauveria bassiana

BACKGROUND

Migration and immunity are behavioral and physiological traits that protect organisms from environmental stressors or pathogen infection. Shifting from migration to residency has become more common in some wildlife populations owing to environmental changes. However, other biological shifts, such as interactions between migration and immunity among populations within a species are largely unexplored for many agricultural migratory pests. In the field, entomopathogenic fungi infection and transmission, particularly Beauveria bassiana, can cause reduced fitness and population declines across a broad range of insect species.

RESULTS

Here, we investigated migration-immunity interactions between migrant and resident populations of the oriental armyworm, Mythimna separata, infected with B. bassiana (the sole fungus used in this work). We found that migratory M. separata exerted stronger pathogen resistance, faster development and lower pupal weight than residents. High-dose infections (5.0 × 105 and 5.0 × 106 conidia mL-1) led to seriously decreased reproductive capacity in migrants and residents. Low-dose infections (1.0 × 104 and 5.0 × 104 conidia mL-1) led to significantly increased host flight capacities. Consecutive flight tests showed that five flight nights inhibited the reproduction of paternal infected M. separata populations. The flights also led to far-reaching transgenerational impairment of larval development and immune defense among offspring populations. By contrast, two flight nights enhanced the reproductive capacities of both M. separata populations and did not exert negative transgenerational effects on offspring populations, which may facilitate migration.

CONCLUSIONS

This study provides insights into interactions between migration and immunity among M. separata populations. These insights will guide development of future monitoring and management technologies of this pest. © 2024 Society of Chemical Industry.

Courtship Behavior of Adult Spodoptera frugiperda (Lepidoptera: Noctuidae) Observed Using Track 3D Trajectory Tracking

Spodoptera frugiperda, also known as the fall armyworm (FAW), is classified by the Food and Agriculture Organization of the United Nations (FAO) as a major agricultural pest. By gaining a more nuanced understanding of the fall armyworm's courtship behavior, simpler and more environmentally friendly methods of controlling this pest can be developed. This study used the Track 3D system to meticulously record and describe the activity characteristics and patterns of adult males and females during courtship. The results show that adult FAWs engaged in a variety of activities during courtship that were either discrete (flying, flapping, moving, and crawling), continuous (flapping + flying, flapping + crawling, and flying + crawling), or combined (flapping + touching + flapping; flying + touching + flying). Flying and flapping were the most common activities, with observed flight patterns consisting of parabolic, circular, and zigzag trajectories. The peak activity times for adult FAWs are mainly concentrated at 11:00 p.m., 3:00 a.m., and 5:00 a.m., providing fundamental data for the precise attraction and control of adult FAWs at later stages.

Invasion and spread of the neotropical leafhopper Curtara insularis (Hemiptera: Cicadellidae) in Africa and North America and the role of high-altitude windborne migration in invasive insects

Invasive insects threaten ecosystem stability, public health, and food security. Documenting newly invasive species and understanding how they reach into new territories, establish populations, and interact with other species remain vitally important. Here, we report on the invasion of the South American leafhopper, Curtara insularis into Africa, where it has established populations in Ghana, encroaching inland at least 350 km off the coast. Importantly, 80% of the specimens collected were intercepted between 160 and 190 m above ground. Further, the fraction of this species among all insects collected was also higher at altitude, demonstrating its propensity to engage in high-altitude windborne dispersal. Its aerial densities at altitude translate into millions of migrants/km over a year, representing massive propagule pressure. Given the predominant south-westerly winds, these sightings suggest an introduction of C. insularis into at least one of the Gulf of Guinea ports. To assess the contribution of windborne dispersal to its spread in a new territory, we examine records of C. insularis range-expansion in the USA. Reported first in 2004 from central Florida, it reached north Florida (Panhandle) by 2008-2011 and subsequently spread across the southeastern and south-central US. Its expansion fits a "diffusion-like" process with 200-300 km long "annual displacement steps"-a pattern consistent with autonomous dispersal rather than vehicular transport. Most "steps" are consistent with common wind trajectories from the nearest documented population, assuming 2-8 hours of wind-assisted flight at altitude. Curtara insularis has been intercepted at US ports and on trucks. Thus, it uses multiple dispersal modalities, yet its rapid overland spread is better explained by its massive propagule pressure linked with its high-altitude windborne dispersal. We propose that high-altitude windborne dispersal is common yet under-appreciated in invasive insect species.