Cronin James T, Strong Donald R
Am Nat. 1999 Jul;154(1):23-36. doi: 10.1086/303221.
The prediction that parasitoid foraging effort should increase with distance traversed to reach or to locate hosts has had little experimental attention. Consistent with a number of models of foraging behavior, we found that the per capita number of ovipositions by the minute fairyfly-egg parasitoid Anagrus sophiae increased significantly with dispersal distance to planthopper hosts in the field in experimental patches of many host eggs. In large continuous stands of cordgrass host plants, after dispersal of decimeters or less, female wasps laid approximately 18% of their average of 18.6 eggs. After dispersal to plants isolated 10 m from other cordgrass, they laid approximately 84%, and they laid virtually all of their eggs after dispersal of 250 m to experimental floating islands of cordgrass. The increased oviposition following dispersal tripled the CV index of aggregation of parasitism to a level theoretically sufficient to promote locally stable parasitoid-host dynamics in isolated patches. At the same time, the change in wasp behavior did not affect the relationship between parasitism and host density, which was consistently density independent. Our results suggest that increased foraging effort with distance traversed can counter Allee effects in colonization and increase spatial spread of populations of natural enemies.
关于寄生性天敌搜寻宿主的努力程度应随着到达或定位宿主所穿越的距离增加而上升这一预测，几乎没有受到实验关注。与许多觅食行为模型一致，我们发现，在许多宿主卵的实验斑块中，微小的仙女蜂卵寄生蜂索菲娅按蚊的人均产卵数随着到稻飞虱宿主的扩散距离在田间显著增加。在大片连续的互花米草宿主植物中，在扩散几分米或更短距离后，雌蜂产下了其平均18.6枚卵中的约18%。在扩散到与其他互花米草相距10米的孤立植物后，它们产下了约84%的卵，而在扩散250米到互花米草实验性浮岛后，它们几乎产下了所有的卵。扩散后产卵量的增加使寄生聚集的CV指数增加了两倍，达到理论上足以促进孤立斑块中局部稳定的寄生性天敌 - 宿主动态的水平。与此同时，黄蜂行为的变化并未影响寄生与宿主密度之间的关系，这种关系始终与密度无关。我们的结果表明，随着穿越距离增加而增加的觅食努力可以对抗定居中的阿利效应，并增加天敌种群的空间扩散。
