| Insects can spread up to hundreds or thousands of meters above ground due to the power of wings. Many agricultural insect pests were found wind-borne and outbreaks were recorded in regions hundreds or thousands of kilometers away from where these insects bred or overwintered. For better understanding the structure of insect community aloft and how it interacted with the insect community near the ground, especially the effects of the wind-borne migration, observations were conducted with a searchlight trap on an island (38 23.200' N, 120 54.500' E) in Changdao, at the center of Baohai channel, in 2002, and with a digital entomological radar and a twin light-trap (simultaneously operated searchlight trap and ground light-trap) at a site in Langfang (39 30'42" N, 116 36'07" E, 28 m asl) , in the vicinity of Beijing, in 2001 and 2002.The present study described the structure of insect community aloft in northern China. It was the first trial to employ the newly equipped migration data acquisition and analysis system for the scanning entomological radar and, a twin light-trap developed in China for, systematic long-term observations of migration of the beet armyworm Spodoptera exigua, beet webworm Loxostege sticticalis and cotton bollworm Helicoverpa armigera in northern China The study provided direct evidence for the migration of 5". exigua in China, many parameters of migratory behaviour of the three species of insects, a better understanding of the relationship between migratory behaviour and wind or temperature field. The results enriched the theory of migration and provided new scientific knowledge for pest management in China.The majority of insect populations trapped on the island were brought from the mainland by winds with several species locally bred. The beet armyworm S. exigua, oriental armyworm Pseudaletia (=Mythimna) separata, cotton bollworm H. armigera and black cutworm Agrotis ipsilon were dominant pest species immigrated into the island, however they emigrated without finding crops. Ladybird Propylaeajaponica & Harmonia axyridis, ground beetle Pseudoophonus griseus and ant lion Chrysopidae were dominant natural enemies migrating with insect pests. Many other species of insect were found to be wind-borne migrants and might produce significant migration. The variation of sex ratio (female to male) with day and time suggested the female moth more powerful in migrating than male S. exigua, P. separata, H. armigera and A. ipsilon.The searchlight trap was found to be an efficient tool for trapping migrants and, operated alongside a ground light-trap, could distinguish migrant from locally-flying species. The ground based light-trap caught large numbers of L. sticticalis on the next evening, after an immigration event, so priority of catching peaks in searchlight trap to ground based light-trap was a good indication of migration.It was confirmed that S. exigua and some other species were high-altitude nocturnal wind-borne migrants in September and October in northern China. Maximum density of moths typically occurred below 500 m, and strong layers were often observed at about 200 m above ground level in airflows which would carry the moths towards the south. Spodoptera exigua descent in the vicinity of the radar site in later September was often associated with rain.The long distance high-altitude wind-borne migration of the beet webworm moths L. sticticalis and short distance dispersal were observed in 2001 and 2002. Catches in both light traps suggested there were five flight periods during our study. Ovary development stage of females in catches and radar observation indicated that L. sticticalis migrated to northeast in early June, to southwest in August and September, and locally-bred moths dispersed over shorter distances in July and August. Collective orientation by the moths was often present in the spring and autumn migration, and the direction of orientation was towards the northeast in spring but to the southwest in autumn.Multi-level layering of migrants was seen every...
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