Effects of genotype and host environment on the cuticular hydrocarbon profiles of Lysiphlebus parasitoids and aggression by aphid-tending ants

Parasitoids in the genus Lysiphlebus specialize on ant-tended aphids and have previously been reported to mimic the CHC profiles of their aphid hosts to avoid detection by ants. However, the precise mechanisms that mediate reduced ant aggression toward Lysiphlebus spp. are not known, nor is it clear whether such mechanisms are broadly effective or specialized to particular aphid hosts. Here we explore the effects of wasp genotype and host environment on Lysiphlebus cuticular hydrocarbon (CHC) profiles and ant aggression. Rearing asexual Lysiphlebus lines in different host aphid environments revealed effects of both wasp line and aphid host on wasp CHCs. However, variation in genotype and host affected different features of the CHC profile, with wasp genotype explaining most variation in linear and long-chain methyl alkanes, while aphid host environment primarily influenced short-chain methyl alkanes. Subsequent behavioral experiments revealed no effects of host environment on ant aggression, but stronger evidence for genotypic effects. The presence of genotypic variation in experienced ant aggression and relevant chemical traits is particularly relevant in light of recent evidence for genetic divergence among Lysiphlebus parasitoids collected from different aphid hosts.

裂头蚜茧蜂属（Lysiphlebus）的寄生蜂专性寄生受蚂蚁抚育的蚜虫，此前已有研究报道该类群可模拟其蚜虫寄主的表皮碳氢化合物（cuticular hydrocarbon, CHC）谱，以躲避蚂蚁的探测。然而，介导裂头蚜茧蜂属物种降低蚂蚁攻击行为的精确机制仍未阐明，且目前尚不清楚此类机制是具备广谱有效性，还是仅对特定蚜虫寄主具有专一性。本研究探究了裂头蚜茧蜂的基因型与寄主环境对其表皮碳氢化合物谱及蚂蚁攻击行为的影响。在不同蚜虫寄主环境中饲养无性系裂头蚜茧蜂品系的实验结果表明，寄生蜂品系与蚜虫寄主均会对蜂类的表皮碳氢化合物谱产生显著影响。不过，基因型与寄主环境分别作用于表皮碳氢化合物谱的不同特征：寄生蜂基因型可解释直链及长链甲基烷烃的绝大多数变异，而蚜虫寄主环境则主要影响短链甲基烷烃的变异。后续开展的行为学实验未发现寄主环境对蚂蚁攻击行为存在影响，但却为基因型的作用提供了更为有力的证据。鉴于近期研究发现从不同蚜虫寄主中采集的裂头蚜茧蜂寄生蜂类群存在遗传分化，寄生蜂在蚂蚁攻击行为相关化学性状上的基因型变异具有尤为重要的研究价值。