The North Wind Epub Download

[Quinton Hebenstreit]

FromGary Paulsen, the author of Hatchet, comes another high-stakes survival story about a young boy on the edge between life and death, where the high seas meet a coastal wilderness.

This stunning historical adventure, set along a rugged coastline centuries ago, does for the sea what Hatchet did for the woods, as it relates the story of a young person's battle to stay alive against the odds.

When a deadly plague decimates his fishing village, an orphan named Leif is forced to take to the water in a cedar canoe. He flees northward, following a wild, fjord-riven shore, navigating from one danger to the next. The deeper into his journey he paddles, the closer he comes to his truest self as he connects to the heartbeat of the ocean, the pulse of the landscape.

With hints of Nordic mythology and an irresistible narrative pull, Northwind is Gary Paulsen at his captivating, adventuresome best.

In warm regions or seasons of the year, the planetary boundary layer is occupied by a huge variety and quantity of insects, but the southward migration of insects (in East Asia) in autumn is still poorly understood.

We collated daily catches of the oriental armyworm (Mythimna separata) moth from 20 searchlight traps from 2014 to 2017 in China. In order to explore the autumn migratory connectivity of M. separata in East China, we analyzed the autumn climate and simulated the autumn migration process of moths.

Southward migration (in the Northern Hemisphere) in autumn was more rarely observed than northward migration, which puzzled early workers [9]. Some researchers believed seasonal poleward shifts to exploit temperate ecosystems represent a population sink from which progeny seldom return [10]. But more recently, increasingly more species have been confirmed to show return migrations in autumn [11,12,13,14,15,16]. For example, using the mark-release-recapture method, Showers et al. [16] proved that black cutworms (Agrotis ipsilon) in America can complete a southward migration of nearly 2000 km in autumn. Chapman et al. [7] estimated through insect trajectory analyses that 80% of the Silver Y moths (Autographa gamma) from the UK can reach warmer latitudes around the northern fringe of the Mediterranean, from approximately 50 N to 40 N. But several independent observations of different migratory insects have shown that the cumulative year-round observations of populations at low latitudes are significantly lower than those at mid-high latitudes [7, 17,18,19]. So, the question arises as to what's affecting the southward migration of insects in the autumn?

Here, we study the oriental armyworm (Mythimna separata Walker), one of the main agricultural pests that undertakes seasonal, long-distance, multigeneration roundtrip and meridional migration in East Asia [24, 25]. Its migration route in China has been clarified through many large-scale mark-release-recapture experiments in the 1960s and 1980s. Each spring, M. separata moths from their overwintering area (south of 0 C isotherm in January) migrate northward into North China, and further into Northeast China (Fig. 1). From mid to late July onwards, part of the M. separata populations from Northeast China have the opportunity to migrate south [24]. The autumn migration of this pest has been observed in August and September by a scanning radar located on an island in the Bohai Gulf, and migrating moths were moving to the southwest [12, 13, 26], but their autumn migration has not been studied at other places. Mythimna separata larvae are most destructive to crops in summer [27], but it is puzzling that larval outbreaks rarely occur in autumn in southern China, despite the huge numbers of the previous generation.

Map of the study area in China. Twenty searchlight traps were set up in 2014, ten of them were located in the overwintering area of M. separata (red points, to the south of 33 N), and other ten were located in the summer breeding area of this pest (blue points)

Currently, insect migrations over large spatial scales are hard to quantify [7, 28]. This study used widely deployed searchlight traps to compare the seasonal population dynamics of M. separata moths at different latitudes, with the aim of elucidating the role of autumn migration in the regulation of the annual migration cycles in this species (and perhaps other migrants in the region).

To monitor the population dynamics of M. separata, the China National Agro-Tech Extension and Service Center has used 19 vertical-pointing searchlights as a monitoring network in different regions of the country since 2014 [29]; at the same time, we also set up a searchlight trap in Ningjin, Shandong province (Fig. 1). Based on years of understanding of the occurrence pattern of M. separata [24, 25, 27], searchlight traps were mainly placed along the migratory route and in the main outbreak areas of M. separata.

We used the HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory Model, ) to simulate the autumn migration of moths. This model was developed to analyze the transport and diffusion of atmospheric pollutants but it has also been used to simulate the migration trajectories of insects such as fall armyworm (Spodoptera frugiperda) and mosquitoes in recent years [18, 32]. Its principle is to regard the insect as a particle that moves with the airflow.

To express the success rate of the southward migration objectively, we estimated two success rates based on the results of trajectory simulation. (1) From the population point of view, we regard the daily captured moths as an emigrating population, and estimated the success rate of this population (i.e., the proportion of endpoints south of 33 N/30 N to the total endpoints from 2014 to 2017). This method may reflect the long-term trend of the success rate more accurately. (2) From the individual point of view, the number of daily catches in the searchlight trap varies greatly during the autumn migration, so each endpoint represents a different number of moths. We estimated the proportion of individuals that successfully returned back to South China in the total catch from the north; this method can reflect the size of the return population more exactly, and there may be large inter-annual differences.

Based on the seasonal characteristics of the searchlight trap catches of M. separata moths in different regions from 2014 to 2017, the seasonal movement in China can be characterized by four waves of migration (Fig. 2A). In the first and second waves, M. separata moths migrated northward and expanded the distribution of the species from its overwintering areas (to the south of 33 N) in South China and the Yangtze River Valley into North China and even Northeast China. Then, the third migration wave occurred between Northeast China and North China in July and August. In the fourth migration wave (from 16 August onwards), moths migrated southward, as shown by the increased catches in the Yangtze Valley and South China (Fig. 2A).

The southernmost endpoints of the trajectories indicated the greatest potential for southward migratory distance, and we hypothesized that moths actively stopped migrating when these endpoint locations were reached. Among these 222 trajectories, 64.9% (144/222) of their southernmost endpoints were located to the south of their origins (Luanxian and Ningjin), and the distance of these southernmost endpoints from their origins were about 2.25 of latitude on average, and no more than 7 of latitude in maximum (Fig. 4C, D). Finally, only 6 trajectories (2.70%) reached the overwintering area (south of 33 N), and none of them reached south of 30 N where moths can breed in winter (Fig. 4C, D). If the daily catches are taken as an indication of emigrant population size and used as a weighting factor, the success rates of M. separata populations returning to the overwintering area were 3.52% and 5.03% in Luanxian and Ningjin, respectively. Not only that, the success rates of return migration estimated from trajectory simulations are close to those from the catches at searchlight traps (Figs. 2, 4). This agreement of the two results, i.e., trajectory simulations and the trap catches, confirms that migrating M. separata moths from North China in the G4 period failed to reach their overwintering area due to unsuitable wind patterns.

Populations of M. separata emerging in late-summer or autumn at high latitudes need to migrate a linear distance of at least 600 km to return to the south of 33 N (Fig. 3B), which is undoubtedly a considerable challenge. Migratory insects have evolved a range of behavioral and physiological strategies to maximize their chances of successfully completing long-range movements to more favorable climes as local conditions deteriorate [28]. For example, numerous migratory insects select favorably-directed tailwinds for southward autumn migrations [3, 6, 7, 28], and newly-emerged rice leaf roller moths (Cnaphalocrocis medinalis), a major pest of rice in southern China, respond to deteriorating conditions such as food shortage by increasing their likelihood of migration in the next few nights compared to well-fed adult moths [36]. By contrast, however, M. separata moths respond to low temperatures and starvation within the first 24 h post-eclosion by shortening their pre-oviposition period (i.e., effectively reducing their window for migration, as the period of greatest flight activity is restricted to the pre-oviposition period) and increasing their fecundity [37]. This suggests that when autumn emigrant M. separata are carried in the wrong direction by prevailing winds, they may terminate their migration and bet-hedge against the risk of harsh environments by increasing the level of reproductive investment. This kind of strategy may explain why so few of the autumn generation of M. separata emigrants reach the permanent winter-breeding region.

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