PNAS:蜂群流失中的螨-病毒互利
意大利那不勒斯大学一项研究提出，在寄生螨与它传播的病毒之间的互惠共生关系是揭示出蜂群流失的动态的关键。人们认为寄生螨狄氏瓦螨(Varroa destructor)和这种螨的病毒乘客——蜜蜂残翅病毒与对养蜂业造成惊人伤害的广泛的蜂群流失有关。此前的研究已经发现，这种螨和它的后代以蜜蜂蛹的血淋巴为食，并且帮助传播了这种病毒，而这种病毒通过下调NF-ĸB蛋白介导的信号传导从而抑制了蜜蜂的免疫力。Francesco Nazzi及其同事测试了病毒诱导的免疫抑制是否促进了螨的觅食，导致在病媒和病原体之间的互利。由于昆虫通过把入侵的寄生虫包裹在一个妨碍它们继续觅食的涂有黑色素的囊中从而对其做出响应，这组作者在被病毒感染的五龄蜜蜂幼虫的体内植入了一个尼龙线，并且对1天之后这个线的黑色素化以及被包裹的程度进行评分。黑色素化和被包裹——以及相关基因的表达水平——与这个幼虫体内的病毒水平负相关。由病毒基因组拷贝数量和螨的后代数量揭示出了病毒水平与螨在蜜蜂蛹上的繁殖正相关，这反映了觅食的收益，提示了病毒感染增强了的螨的生殖适应度。这组作者说，这种螨-病毒的共生——这种关系促进了螨的觅食和生殖——是解开蜜蜂群流失的神秘病因的一个关键。
原文链接：
A mutualistic symbiosis between a parasitic mite and a pathogenic virus undermines honeybee immunity and health
原文摘要：
Honey bee colony losses are triggered by interacting stress factors consistently associated with high loads of parasites and/or pathogens. A wealth of biotic and abiotic stressors are involved in the induction of this complex multifactorial syndrome, with the parasitic mite Varroa destructor and the associated deformed wing virus (DWV) apparently playing key roles. The mechanistic basis underpinning this association and the evolutionary implications remain largely obscure. Here we narrow this research gap by demonstrating that DWV, vectored by the Varroa mite, adversely affects humoral and cellular immune responses by interfering with NF-κB signaling. This immunosuppressive effect of the viral pathogen enhances reproduction of the parasitic mite. Our experimental data uncover an unrecognized mutualistic symbiosis between Varroa and DWV, which perpetuates a loop of reciprocal stimulation with escalating negative effects on honey bee immunity and health. These results largely account for the remarkable importance of this mite–virus interaction in the induction of honey bee colony losses. The discovery of this mutualistic association and the elucidation of the underlying regulatory mechanisms sets the stage for a more insightful analysis of how synergistic stress factors contribute to colony collapse, and for the development of new strategies to alleviate this problem.
作者：Gennaro Di Prisco
