对于蚂蚁的幼蚁和蛹而言，患病就等于接到死亡判决。当成年蚂蚁从它们一尘不染的巢穴中辨认出一只生病的衰弱蚂蚁后，它们仅仅会将病蚁搬出巢穴，让其自生自灭。
就像专业术语说的那样，这种极端的“卫生行为”是在拥挤的昆虫巢穴中，抑制疾病暴发的一种有效方式。但是，研究人员在《BMC进化生物学》上报道说，一些蚂蚁蛹找到了一种方法，使得它们能避免被巢穴驱逐——通过在防止细菌的茧蛹中生长，并以此躲避疾病。
一直以来，科学家希望能够知道，为何在一些蚂蚁物种中，蛹会吐丝结茧，包裹起自己的身体，然而在其他蚂蚁种群中，蛹却是裸露的。在一些奇怪的案例中，蚂蚁甚至还能左右逢源：在相同的蚂蚁种群里，一些蛹会建造茧，但是其他一些却没有。
当研究人员利用致命真菌感染了不同的蚂蚁物种后（有茧的、裸露的或“犹豫不决”的蛹），成年蚂蚁很快将生病的卵搬出巢穴。
但是，结果显示，有茧的蛹通常被留了下来，并且即使它们仍然暴露在真菌中，这些蚂蚁蛹也不会生病。
研究人员推测，这些茧就像是盾牌，帮助蛹抵御真菌的入侵。对于蚂蚁而言，这真是一个双赢的局面：蛹不会牺牲，而蚂蚁群体也能免于流行病的威胁。(生物谷Bioon.com)
生物谷推荐的英文摘要
BMC Evolutionary Biology doi:10.1186/1471-2148-13-225
Pupal cocoons affect sanitary brood care and limit fungal infections in ant colonies
Simon Tragust, Line V Ugelvig, Michel Chapuisat, Jürgen Heinze and Sylvia Cremer
Background
The brood of ants and other social insects is highly susceptible to pathogens, particularly those that penetrate the soft larval and pupal cuticle. We here test whether the presence of a pupal cocoon, which occurs in some ant species but not in others, affects the sanitary brood care and fungal infection patterns after exposure to the entomopathogenic fungus Metarhizium brunneum. We use a) a comparative approach analysing four species with either naked or cocooned pupae and b) a within-species analysis of a single ant species, in which both pupal types co-exist in the same colony.
Results
We found that the presence of a cocoon did not compromise fungal pathogen detection by the ants and that species with cocooned pupae increased brood grooming after pathogen exposure. All tested ant species further removed brood from their nests, which was predominantly expressed towards larvae and naked pupae treated with the live fungal pathogen. In contrast, cocooned pupae exposed to live fungus were not removed at higher rates than cocooned pupae exposed to dead fungus or a sham control. Consistent with this, exposure to the live fungus caused high numbers of infections and fungal outgrowth in larvae and naked pupae, but not in cocooned pupae. Moreover, the ants consistently removed the brood prior to fungal outgrowth, ensuring a clean brood chamber.
Conclusion
Our study suggests that the pupal cocoon has a protective effect against fungal infection, causing an adaptive change in sanitary behaviours by the ants. It further demonstrates that brood removal?originally described for honeybees as ?hygienic behaviour??is a widespread sanitary behaviour in ants, which likely has important implications on disease dynamics in social insect colonies.
