Hare James F, Eisner Thomas
Section of Neurobiology and Behavior, Cornell University, Seeley G. Mudd Hall, 14853-2702, Ithaca, NY, USA.
Oecologia. 1993 Oct;96(1):9-18. doi: 10.1007/BF00318024.
To examine the chemical defense of lepidopteran eggs towards ant predators, eggs of the arctiid moth Utetheisa ornatrix were offered to laboratory colonies of the ant Leptothorax longispinosus. The ants rapidly devoured Utetheisa eggs produced by parents reared on an alkaloid-free diet, but left eggs that had been endowed with parental alkaloid largely unmolested. That defense can be attributed directly to the presence of a pyrrolizidine alkaloid since topical application of monocrotaline in either its free base or N-oxide state conferred protection on otherwise palatable eggs. The N-oxide and free base were not equally effective in conferring protection however; free-base treated eggs were subject to greater predation than N-oxide treated eggs after 24 h. The emergence of differential alkaloid effectiveness only after prolonged exposure is consistent with the notion that chemical protection is seldom absolute. That difference was resolved only when the otherwise food-deprived ants exceeded a certain threshold of hunger. The efficacy of applied monocrotaline as a predator deterrent increased with increasing concentration of N-oxide, but was lowest for eggs treated with an intermediate concentration of free base. The latter concentration effect likely represents an artefact of the behaviour of the ant colonies offered eggs treated with an intermediate concentration, as those colonies were the most voracious predators in reference tests with palatable eggs. In addition to the immediate deterrent value of pyrrolizidine alkaloid, ant colonies that had been exposed to alkaloid-laden eggs subsequently avoided even palatable, unprotected eggs offered 33 days later. Our data provide the first demonstration of such long-term avoidance of chemically protected lepidopteran prey by an invertebrate. The discovery of a mechanism promoting learned avoidance on the part of ant predators has important ramifications to egg-laying strategies of female Utetheisa, both in terms of the dispersion of eggs, and the extent to which eggs are provisioned with alkaloid.
为了研究鳞翅目昆虫卵对蚂蚁捕食者的化学防御，将灯蛾Utetheisa ornatrix的卵提供给长刺蚁Leptothorax longispinosus的实验室群体。蚂蚁迅速吞食了以无生物碱饮食饲养的亲本所产的Utetheisa卵，但对含有亲本生物碱的卵基本未加侵扰。这种防御可直接归因于吡咯里西啶生物碱的存在，因为以游离碱或N-氧化物形式局部施用野百合碱可为原本可口的卵提供保护。然而，N-氧化物和游离碱在提供保护方面的效果并不相同；24小时后，经游离碱处理的卵比经N-氧化物处理的卵遭受更多捕食。仅在长时间暴露后才出现生物碱效果差异，这与化学保护很少是绝对的观点一致。只有当原本缺乏食物的蚂蚁超过一定饥饿阈值时，这种差异才会消除。施用的野百合碱作为捕食者威慑剂的功效随着N-氧化物浓度的增加而增加，但对于用中等浓度游离碱处理的卵，其功效最低。后一种浓度效应可能代表了用中等浓度处理的卵所提供给蚁群行为的一种假象，因为在对可口卵的参考测试中，那些蚁群是最贪婪的捕食者。除了吡咯里西啶生物碱的直接威慑价值外，接触过含生物碱卵的蚁群随后甚至会避开33天后提供的可口、未受保护的卵。我们的数据首次证明了无脊椎动物对化学保护的鳞翅目猎物有这种长期回避行为。发现一种促进蚂蚁捕食者学习回避的机制，对雌性Utetheisa的产卵策略具有重要影响，无论是在卵的分散方面，还是在卵中生物碱的供应程度方面。
