Moniuszko Hanna, Mąkol Joanna
Department of Invertebrate Systematics and Ecology, Institute of Biology, Wrocław University of Environmental and Life Sciences, Kożuchowska 5b, 51-631, Wrocław, Poland.
Parasit Vectors. 2016 Feb 2;9:61. doi: 10.1186/s13071-016-1339-2.
The time-extended contact of trombiculid larvae with hosts poses a question of its ecological determinants. The phenomenon, which may facilitate the overwintering of larvae in the temperate zone, was previously observed in few parasitengone taxa, but not confirmed for mammal-associated trombiculids. The study aims at tracing the phenology of larvae of Hirsutiella zachvatkini and at verifying the hypothesis of contact with the host, extending beyond the parasitic phase.
Apodemus agrarius, Apodemus flavicollis and Myodes glareolus, trapped during 2-year studies, were checked for the presence of trombiculid larvae. Larvae of H. zachvatkini served for the studies. The degree of mites' engorgement was checked over time in order to estimate the duration of feeding phase and to measure the maximum size increase. The experimental rearing aimed at ascertaining the relations between the level of engorgement and successful transformation of larva into subsequent instar.
The mass appearance of larvae on hosts fell on autumn and winter, with a decrease observed in spring, leading to an almost total absence in early and mid summer. The highest intensity, attained in late autumn or in winter, was not followed by further increase in the number of host-associated larvae. The percentage of unengorged larvae on hosts was disproportionately small, irrespective of the season. The size increase of larva was 12.6-fold at maximum. Engorged or partly engorged larvae, observed from the beginning of mass appearance over the entire period of host-parasite association in the field, transformed into subsequent instar when removed from host.
An increase in intensity observed from the onset of appearance of larvae on hosts, through autumn and winter months, at rarity of observations of unengorged larvae and absence of engorged larvae off-host, indicates a prolonged contact with hosts, aimed at synchronisation of life cycle, conditioned by food resources available for active postlarval forms and constitutes a strategy enabling larvae to survive the unfavourable winter conditions. The proportion of engorged and partly engorged vs. unfed larvae, observed over the survey, along with their ability to transform into subsequent instars, indicates a relatively short feeding phase. The lack of continuous increase in abundance and intensity towards spring and summer suggests a gradual detachment of partly and fully engorged larvae which attained the readiness to subsequent development. The size increase of larvae during their parasitic phase does not corroborate the neosomy in H. zachvatkini. Host-associated differences in topic preferences of the chiggers become less obvious at maximum infection rates. Quantitative descriptors of parasite population place M. glareolus among the most infected hosts of H. zachvatkini in contrast to Apodemus mice collected in the same habitat.
恙螨幼虫与宿主的长时间接触引发了其生态决定因素的问题。这种可能有助于温带地区幼虫越冬的现象，此前在少数寄螨类群中被观察到，但尚未在与哺乳动物相关的恙螨中得到证实。本研究旨在追踪扎氏赫氏螨幼虫的物候，并验证与宿主接触超出寄生阶段这一假说。
在为期两年的研究中捕获的黑线姬鼠、黄颈姬鼠和林姬鼠，检查是否存在恙螨幼虫。以扎氏赫氏螨幼虫作为研究对象。随着时间推移检查螨的饱食程度，以估计取食阶段的持续时间并测量最大体型增长。实验饲养旨在确定饱食程度与幼虫成功转化为后续龄期之间的关系。
幼虫在宿主上大量出现集中在秋季和冬季，春季数量减少，导致在夏初和仲夏几乎完全没有。在深秋或冬季达到的最高强度之后，与宿主相关的幼虫数量并未进一步增加。无论季节如何，宿主上未饱食幼虫的比例都出奇地小。幼虫的体型最大增加了12.6倍。从大量出现开始在野外宿主 - 寄生虫关联的整个时期观察到的饱食或部分饱食的幼虫，在从宿主移除后会转化为后续龄期。
从幼虫在宿主上出现开始，经过秋冬季节，未饱食幼虫的观察稀少且离开宿主后没有饱食幼虫，观察到的强度增加表明与宿主的接触时间延长，目的是使生命周期同步，这取决于可供活跃的幼虫后形态利用的食物资源，并且构成了一种使幼虫能够在不利的冬季条件下存活的策略。在调查中观察到的饱食和部分饱食与未取食幼虫的比例，以及它们转化为后续龄期的能力，表明取食阶段相对较短。向春季和夏季丰度和强度没有持续增加，表明部分和完全饱食的幼虫逐渐脱离，它们已准备好进入后续发育阶段。幼虫在寄生阶段的体型增加并不支持扎氏赫氏螨的新体现象。在最大感染率时，恙螨在宿主上偏好部位的宿主相关差异变得不那么明显。寄生虫种群的定量描述表明，与在同一栖息地收集的姬鼠属小鼠相比，林姬鼠是扎氏赫氏螨感染最严重的宿主之一。
