Parasitism patterns of parasitoid wasps in forests and the spatiotemporal structure of the host-parasitoid systems.

本文研究了两种寄生蜂（膜翅目，小蜂科）资源利用的时空格局和性比操纵与寄主大小的关系。这两种寄生虫都寄生在日本松树树干的皮层下甲虫上。发起者的平均体重是短尾螺的8倍，产卵者的长度是短尾螺的3.7倍。在这两种寄生蜂中，羽化蜂的大小与寄主的大小均呈正相关，但三种主要寄主的大小与羽化蜂的大小均呈线性关系，而在较大的寄主中，羽化蜂的大小与羽化蜂的大小呈对数关系。两种寄主的性别比（雄性比例）均随寄主大小的增加而降低，但在各寄主上的总体性别比均表现为雄性偏雄，而短叶假丝蛾则表现为雌性偏雄。寄主消耗的比例如何随寄主大小的变化而变化，并在同一种寄主的两种拟寄主之间存在差异。在野外调查中，从一棵死树中出现的两种寄生蜂的大小和性别比例与寄主的大小密切相关。两种寄生蜂的空间分布与树干的树皮厚度有关。这些数据表明，寄主大小和产卵器长度的相对评价差异可能是两种寄生蜂共存的原因。在对枯死松树的调查中，寄生蜂在皮层下甲虫上的垂直分布由松树的树皮厚度和寄生蜂的飞行能力共同决定，其中在离地3 ~ 5m高的树干上寄生蜂最多。

Spatiotemporal patterns of resource utilization and sex ratio manipulation in relation to host size were investigated for two solitary ectoparasitoid wasps, Atanycolus initiator and Spatius brevicaudis (Hymenoptera, Braconidae). Both species parasitize subcortical beetles on the trunks of Japanese pine trees. A.initiator is on average 8 times larger in body weight and has an ovipositor that is 3.7 times longer than that of S.brevicaudis. In both parasitoids, the size of emerging wasps was positively correlated with host size, but the host/wasp size regressions were linear for all three major host species in A.initiator, whereas in S.brevicaudis the regression was logarithmic for a relatively large host species. The sex ratios (proportion of males) of both parasitoids emerging from different host species decreased with increasing host size, but the overall sex ratio on each host species was male-biased in A.initiator, while female-biased in S.brevicaudis. How the proportion of host consumed changed in response to host size and differed between the two parasitoids for the same host species. In the field survey, the size and sex ratio of the emerging two parasitoids from a dead tree were closely related to host size. However, the spatial distribution of the two parasitoids depended on the bark thickness of the trunk. The data suggested that differences in the relative evaluation of host size and in ovipositor lenght may enable to the coexistence of the two parasitoid wasps. In another survey on dead pine trees, the vertical distribution of parasitoid wasps on subcortical beetles, which wasps occurred most abundantly on the trunk of 3-5m high above the ground, was suggested to be determined by both bark thickness of pine trees and flight ability of the wasps.