西藏飞蝗蝗蝻群集迁移特性及其群集效应

西藏飞蝗Locusta migratoria tibetnsis Chen暴发成灾的重要原因之一是蝗蝻具有群集迁移危害习性。为阐明西藏飞蝗灾变的行为机制，为西藏飞蝗的监测预警和防治提供科学依据，利用视频跟踪技术测定了自然环境中西藏飞蝗蝗蝻群集迁移的运动速度、方向，建立自推进粒子模型模拟蝗蝻群集迁移行为，分析群集迁移效应。结果表明，①不同自然环境中的西藏飞蝗蝗蝻在群集迁移过程中，群体内个体的运动表现出定向集体运动，群集迁移速度为0.1256 m/s，0.2 m以内的个体蝗蝻方向趋向一致。沙滩、翻耕农田和草地蝗蝻群运动一致性参数均较高，分别为0.8502、0.7870和0.6987。②西藏飞蝗蝗蝻群由分散运动转变为群集迁移存在临界密度，密度较低时群体内个体分散运动，当蝗蝻密度达到12-15头/m²时，蝗蝻群体由分散运动转变为高度一致的群集迁移运动。③蝗蝻群通过群集迁移可以显著增加迁移距离，随机运动蝗蝻1 d扩展只有70-80 m，而群集迁移1 d最大距离可达2.5 km。蝗蝻群集迁移可以提高发现特别是远距离食物等资源的概率，使群体中更多的个体受益。④尽管未发现室外蝗蝻群存在先验个体，但模拟发现在群集迁移群体中，只需要少数先验个体（3%-5%）即可引导整个蝗蝻群运动。

Effects of migration and aggregation of Locusta migratoria tibetnsis nymphs

One of the important reasons for severe infestations of Locusta migratoria tibetnsis Chen was that the locust nymphs have the habit of aggregation migration. In order to elucidate the mechanism of migration of locust nymphs and to provide a scientific basis for the control of this pest, we applied visual tracking to measure the speed and direction of movement of the migratory locust nymphs in the fields. Then we set a self-propelled particle model (SPP) to simulate the migratory behavior of locust nymphs, and the characteristics of migration were analyzed. The results show that the movement of individuals in the group would show the directional collective movement to a certain extent during the migration of L. migratoria tibetnsis in different natural environments such as sandy beach, grassland and farmland. The average speed of movement of migratory locust nymphs was 0.1256 m/s, and the movement direction of individual nymphs within interaction radius 0.2 m tended to be aligned. The normalized alignments of migrating movement were 0.8502 in sandy beach, 0.7870 in farmland and 0.6987 in grassland, which showed that migratory locust swarms was highly aligned in collective motion. Next, as the density of nymphs in the group increased up to the critical density 12-15 locusts/m², a transition took place from the disordered movement of individuals within the group to highly aligned collective motions. Due to the reduction of random movement, the migration distance of orderly migrating individuals could be significantly increase to about 2.5 km per day, meanwhile that of disorder movement individuals was only 70-80 m. Therefore, the orderly migrating nymphs improved the probability of achievement of food and other useful resources. When individuals were far away from food, those who moved disorderly could hardly find food. Finally, although no experienced individuals were found in outdoor locust swarm, our model revealed that only a very small proportion (about 3%-5%) of the informed individuals could guide the marching group of locust successfully.