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

研究了两种孤立的体外寄生蜂--小蜂和短尾小蜂性比操纵与寄主大小关系的时空格局。这两个物种都将皮层下甲虫寄生在日本松树的树干上。A.Initiator的平均体重是S.brevicaudis的8倍，产卵器的长度是S.brevicaudis的3.7倍。在两种寄生蜂中，羽化蜂的大小与寄主大小均呈正相关，但三种主要寄主种类的寄主/黄蜂大小回归均呈线性关系，而在短尾小蜂中，较大的寄主种类则呈对数回归。不同寄主种类的两种寄生蜂的性比(雄蜂比例)均随寄主大小的增加而降低，但各寄主种类的总性比在启动器上是偏向男性的，而在短尾小蜂上是偏向雌性的。寄主的消耗比例随寄主大小的变化而变化，对于同一寄主种类，两种寄生蜂间的比例也不同。在田间调查中，从一棵枯树上出现的两种寄生蜂的大小和性别比与寄主大小密切相关。但两种寄生蜂的空间分布取决于树干的树皮厚度。这些数据表明，寄主大小和产卵器长度的相对评价的差异可能使两种寄生蜂共存。在另一次对枯死松树的调查中，皮下小蜂上的寄生蜂的垂直分布被认为是由松树树皮厚度和黄蜂的飞行能力共同决定的，皮下小蜂在离地面3-5m的树干上最多。

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.