Rank Nathan Egan
Department of Zoology, University of California-Davis, 95616, Davis, CA, USA.
The White Mountain Research Station, University of California, 93514, Bishop, CA, USA.
Oecologia. 1994 Apr;97(3):342-353. doi: 10.1007/BF00317324.
Several species of willow leaf beetles use hostplant salicin to produce a defensive secretion that consists of salicylaldehyde. Generalist arthropod predators such as ants, ladybird beetles, and spiders are repelled by this secretion. The beetle larvae produce very little secretion when they feed on willows that lack salicylates, and salicin-using beetles prefer salicylate-rich willows over salicylate-poor ones. This preference may exist because the larvae are better defended against natural enemies on salicylate-rich willows. If this is true, the larvae should survive longer on those willows in nature. However, this prediction has not been tested. I determined the larval growth and survival of Chrysomela aeneicollis (Coleoptera: Chrysomelidae) on five willow species (Salix boothi, S. drummondiana, S. geyeriana, S. lutea, and S. orestera). These species differed in their salicylate chemistries and in leaf toughness but not in water content. The water content varied among the individual plants. Larval growth of C. aeneicollis did not differ among the five species in the laboratory, but it varied among the individual plants and it was related to the water content. In the field, C. aeneicollis larvae developed equally rapidly on the salicylate-poor S. lutea and on the salicylate-rich S. orestera. Larval survival was greater on S. orestera than on S. lutea in one year (1986), but there was no difference between them during three succeeding years. In another survivorship experiment, larval survival was low on the medium-salicylate S. geyeriana, but high on the salicylate-poor S. boothi and on S. orestera. Larval survival in the field was related to the larval growth and water content that had been previously measured in the laboratory. These results showed that the predicted relationship between the host plant chemistry and larval survival did not usually exist for C. aeneicollis. One possible reason for this was that the most important natural enemies were specialist predators that were unaffected by the host-derived defensive secretion. One specialist predator, Symmorphus cristatus (Hymenoptera: Eumenidae), probably caused much of the mortality observed in this study. I discuss the importance of other specialist predators to salicin-using leaf beetles.
几种柳叶甲虫利用寄主植物中的水杨苷来产生一种由水杨醛组成的防御性分泌物。像蚂蚁、瓢虫和蜘蛛等多食性节肢动物捕食者会被这种分泌物驱赶。当甲虫幼虫取食缺乏水杨酸盐的柳树时，它们分泌的物质很少，而且利用水杨苷的甲虫更喜欢富含水杨酸盐的柳树，而不是水杨酸盐含量低的柳树。这种偏好可能存在是因为幼虫在富含水杨酸盐的柳树上能更好地抵御天敌。如果这是真的，那么幼虫在自然环境中应该在那些柳树上存活更长时间。然而，这一预测尚未得到验证。我测定了铜绿叶甲（鞘翅目：叶甲科）在五种柳树（博思柳树、德拉蒙德柳树、盖耶柳树、黄柳树和奥雷斯特柳树）上的幼虫生长和存活情况。这些柳树在水杨酸盐化学组成和叶片韧性上存在差异，但在含水量上没有差异。不同植株之间含水量有所不同。在实验室中，铜绿叶甲的幼虫生长在这五个柳树品种间没有差异，但在不同植株间存在差异，并且与含水量有关。在野外，铜绿叶甲幼虫在水杨酸盐含量低的黄柳和水杨酸盐含量高的奥雷斯特柳上发育速度相同。在一年（1986年）里，奥雷斯特柳上的幼虫存活率高于黄柳，但在随后的三年里它们之间没有差异。在另一个存活实验中，水杨酸盐含量中等的盖耶柳上幼虫存活率低，但水杨酸盐含量低的博思柳和奥雷斯特柳上幼虫存活率高。野外幼虫的存活与之前在实验室中测量的幼虫生长和含水量有关。这些结果表明，对于铜绿叶甲来说，寄主植物化学组成与幼虫存活之间预测的关系通常并不存在。一个可能的原因是最重要的天敌是专食性捕食者，它们不受寄主衍生的防御性分泌物的影响。一种专食性捕食者，晶形胡蜂（膜翅目：蜾蠃科），可能是本研究中观察到的大部分死亡的原因。我讨论了其他专食性捕食者对利用水杨苷的叶甲虫的重要性。
