Interaction between genetic and inductive factors controlling the expression of dispersal and dormancy morphs in dimorphic astigmatic mites

Some astigmatic mites display dimorphic deutonymphs (hypopus) which are facultatively intercalated in their development cycle between protonymph and tritonymph. Such species, among them Glycyphagus privatus and Glycyphagus ornatus show three potential developmental pathways: (1) to bypass the hypopus stage and develop directly from the protonymph to the tritonymph and the subsequent reproductive stage when conditions are favorable; (2) to leave the original site and disperse by means of a phoretic hypopus morph; or (3) to survive inimical life conditions in the natal environment by means of a sedentary hypopus morph. By producing both dispersing (and afterwards at the arrival site reproducing) and sedentary (drought-hardy and dormancy-prone) progeny each single parent attains a selective advantage through a risk-reducing insurance against irregularly fluctuating and often fatal life conditions of their temporary patch habitats. Both genetic heterogeneity and ecological plasticity for hypopus production adapt the Glycyphagus species to cope with variation in the environment. Both traits (for dispersal and survival) are extremely polymorphic with genotypes ranging from low to high propensities for production of each hypopus type. There is a substantial environmental effect on genetic expression such that expression of both morphs depends on the quality of food. This ecological response allows a fast reaction of the mite to the current trophic environment. Phoretic morphs are predominantly expressed at favorable trophic conditions and sedentary morphs at poor trophic conditions. Ecological influences may override genetic propensities and vice versa. Although selection imposed by changing environmental patterns adjusts the frequencies of genotypes over generations and provides for long-term adaptation, the short-term process of environmental induction adapts the population within a generation to transient-habitat disturbances. The interaction of genetic and ecological determinants explains the varying proportions of directly developing mites, phoretic hypopodes, and sedentary hypopodes, in a population at any moment.     

伯氏嗜木螨各发育阶段的外部形态扫描电镜观察

【目的】 观察伯氏嗜木螨Caloglyphus berlesei生活史各发育阶段外部形态和超微形态特征。【方法】 采集中华地鳖Eupolyphaga sinensis培养床上的培养料, 分离伯氏嗜木螨。将分离获得的伯氏嗜木螨双蒸水洗涤后, 一部分用于制备常规玻片标本, 光镜下直接观察; 另一部分用2.5%戊二醛溶液固定, 70%酒精再次洗涤, 临界点干燥, 置于扫描电镜下观察不同发育阶段（包括卵、 幼螨、 若螨及成螨）的超微形态特征。【结果】 电镜下伯氏嗜木螨各发育阶段的足、 刚毛和外生殖器及其附属结构的形态均清晰可辨。幼螨足3对, 足上无叶状刚毛, 基节干发达; 若螨足4对, 出现第4背毛, 生殖区发育不全; 休眠体足爪和前跗节发达, 出现叶状毛、 胫节毛及膝节毛等结构, 生殖板骨化明显, 其两侧有吸盘和刚毛各1对。吸盘板上共有4对成对的吸盘、 1个单吸盘和2对类圆形微凸。成螨生殖感觉器骨化且呈心形, 雄雌成螨生殖感觉器的刚毛数量上有明显差异。【结论】 对伯氏嗜木螨形态和超微形态特征的观察有助于对其进一步科学分类和进行生活史研究, 并可为控制伯氏嗜木螨及其引起的过敏性疾病提供参考。     

螨类休眠体的发育与治理

休眠体是螨类抵御不良环境并借助携播者进行传播的特殊形式,许多非痒螨股的无气门目螨类都有此现象。休眠体形成和解除由遗传因素决定,也受到一种或多种环境因素的影响,如温度、湿度、营养和密度等,但各种因素对不同的螨类所起的作用不同;环境与遗传基因的相互作用是决定休眠体形成与解除的关键。一些易形成休眠体的螨类是生产和生活中的重要害虫,它们表皮构造特殊、个体微小,给防治和检疫工作造成了很大困难。为此,本文对休眠体的发生、传播、生长发育和防治等方面的研究概况进行了回顾。