粘虫发生规律的研究Ⅴ——粘虫季节性远距离迁飞的一个模式

本文提出了一个粘虫季节性远距离迁飞的模式图。粘虫在广东、广西省1—2月間发生一个世代,为害小麦。这一代羽化的成虫(可能还有湖南、福建等地越冬幼虫羽化的成虫)于3—4月間向北迁飞:绝大多数迁到江苏、安徽、河南及山东南部地区,并在該地繁殖为害,产生第二代;一部分可能迁至河北、山东北部、山西、豫北等地,在这些地区也能繁殖一代,但因环境条件不适合,基本上不为害;一小部分甚至于可以迁至更北地区,如东北中北部,但在这些地区不能生存繁殖。在江苏北部、河南等地繁殖后的第二代成虫,在5—6月间又向北迁飞,这就成为东北地区的主要为害世代。在河北、山西等地,除了有这批迁移来到的蛾子外,尚有当地繁殖的后代,因而有世代重迭現象。在东北为害世代的成虫在7—8月間向南迁飞:一部分可能在东北南部(如錦州等地)再繁殖为害一代;但多数迁到河北、山东、山西等地。这一代的成虫在9月間再迁向南方,到湖南、福建、广东、广西等地,为害晚稻。在湖南、湖北、福建等地,该代的幼虫越冬,在广东、广西地区,再繁殖一代。一般说来,在粘虫迁飞后的地区,虫量大为減少,以至几乎不能找到,春季向北迁移与秋季向南迁移可能有所不同。在向北迁移中,每代迁移之后、数量都有增加;而在向南迁移中,数量增加是不显著的;这可能是由于迁移中有稀释或分散至更大地区的原因。根据这一模式图,許多有关粘虫发生的現象可以获得解释:如不同地区猖獗世代的不同,猖獗时間的不同,东北地区早春蛾子发生的特点,蛾子发生高峯的类型,各地区的世代数等。本文并根据这一模式图討論了对于数量变动及預测預报的意义。

STUDIES ON THE REGULARITIES OF THE OUTBREAK OF THE ORIENTAL ARMYWORM (LEUCANIA SEPARATA WALKER) V. A Model for Seasonal Long-distance Migration of the Oriental Armyworm

A hypothetical model for the seasonal long distance migration of the Oriental Armyworm (Leucania separata Walker) was proposed. The general scheme is (Figure 1):The first generation occurs in Kwangtung, Kwangsi in January and February causing damage to spring wheat; moths of this generation and those from the overwintering larvae in Fukien, Hunan and their vicinities migrate northward in March and April; they arrive at Kiangsu, Anwhei, Honan and southern Shantung and multiply for the second generation causing damage to wheat there. A part of them migrate further north to Hopei, northern Shantung and Shansi where they may poorly survive as the second generation; and still others may eventually migrate still farther north, but they generally fail to produce another generation. From Kiangsu, Anwhei, Honan, etc., moths of the second generation migrate northward in May and June, they constitute the most important and injurious generation in the Northeast. In Hopei, Shansi, etc., this so-called second generation may consist of local descendents of the preceding migrants, but the immigrating moths of the second generation are preponderant. Moths of the third generation migrate southward in July and August from the Northeast; part of them may establish themselves in the southern part of the Northeast (e.g., Chinchow), becoming the so-called autumn generation of that district; but most of them migrate farther south to Hopei, Shansi, etc.. Moths of the fourth generation migrate in September to Hunan, Hupei, Fukien, Kwangsi and Kwangtung, where they bring damage to late rice crops. In Hunan and Hupei, the larvae of this generation overwinter in rice fields and other grass fields; in Kwangtung, probably also Kwangsi, they produce another generation. In general, when armyworm moths migrate out from one place, the number of insects left in that place becomes very greatly reduced or so rare as can hardly be found. In the spring northward migration, the number of insects increases in succeeding generations, but in the autumn southward migration, the number of insects increases but little, owing probably to the dispersal to larger areas. If this hypothetical model is accepted a number of phenomena can be easily explained, such as the differences of the numbers of outbreaks and differences in the time of outbreak in different regions from south to north, the failure to find overwintering insects and the long duration in the appearance of adult moths in early spring in the Northeast, the number of generations and the apparent lack of continuity in the different generations in South China. Further implications of this hypothetical model on the relative abundance and its significance on forecasting were discussed.