Data from: The role of host phenology in determining the incidence of an insect sexually transmitted infection

Changes in the timing of life history events within the year alter the degree to which the activity patterns of different species coincide, making the dynamics of interspecific interactions sensitive to the phenology of the interacting parties. For parasites, the availability of suitable hosts to infect represents a crucial determinant of dynamics, and changes in the host (and parasite) phenology may thus alter disease epidemiology and the conditions for disease maintenance. We tested the hypothesis that the incidence of a sexually transmitted mite infection, Coccipolipus hippodamiae, in Adalia bipunctata ladybird beetles in Sweden was determined by host phenology, namely presence/absence of sexual contact between cohorts of the host. We observed that the pattern of mite presence/absence across Swedish A. bipunctata populations was highly reproducible between years, implying a persistent biological/ecological basis underlying the incidence. Further, ladybirds from populations where the mite was absent were able to acquire mites during copulation, develop a mite infection, and transmit infection onward, indicating an ecological (rather than biological) driver of mite incidence. Observations of ladybird phenology in natural populations provided evidence of sexual contact between overwintered and new cohort adults in populations where the mite was present. In contrast, new cohort ladybirds in the two northern Swedish populations where the mite was not present had not had sexual contact with the overwintered generation, creating a ‘hard stop’ to mite transmission. We conclude that variation in host phenology may be an important driver of the incidence of sexually transmitted infections (STIs) by determining the presence/absence of sexual contact between generations. More generally, we hypothesize that sensitivity to variation in host phenology will be highest for parasites like STIs that infect one host species, one host life stage and are directly transmitted on contact between host individuals.年内生活史事件的时间节律改变，会改变不同物种种群活动模式的重合程度，使得种间相互作用动态对互作双方的物候（phenology）敏感。对于寄生物而言，适宜宿主的可获得性是其种群动态的关键决定因素，因此宿主（以及寄生物自身）的物候变化可能会改变疾病流行病学特征与疾病维持的条件。我们检验了如下假说：瑞典双斑瓢虫（Adalia bipunctata）种群内的性传播螨类感染（Coccipolipus hippodamiae）发生率，由宿主物候决定，具体而言即宿主不同世代间是否存在性接触。我们观察到，瑞典双斑瓢虫种群的螨类感染有无模式在年间具有高度可重复性，这暗示感染发生率背后存在稳定的生物学/生态学基础。进一步研究发现，未感染螨类的种群来源的瓢虫，可通过交配获得螨类、发展出螨类感染，并将感染传播给其他个体，这表明螨类发生率的驱动因素为生态学层面（而非生物学层面）。对自然种群中瓢虫物候的观测表明，在存在螨类的种群中，越冬代成虫与新世代成虫之间存在性接触。与之相对，瑞典北部两个未发现螨类的种群中，新世代瓢虫并未与越冬代发生性接触，这为螨类传播设置了“硬性阻断”。我们由此得出结论：宿主物候的差异可通过决定世代间性接触的有无，成为性传播感染（sexually transmitted infections, STIs）发生率的重要驱动因素。更广泛而言，我们提出假说：对于仅感染单一宿主物种、单一宿主生活史阶段，且依赖宿主个体间直接接触传播的寄生物（如性传播感染），其对宿主物候变化的敏感性将达到最高。