Joost P Houston, Backus Elaine A, Morgan David, Yan Fengming
Department of Entomology, University of Riverside, Riverside, CA 92521, USA.
J Insect Physiol. 2006 Mar;52(3):327-37. doi: 10.1016/j.jinsphys.2005.11.012. Epub 2006 Jan 19.
Glassy-winged sharpshooter, Homalodisca coagulata (Say), is an efficient vector of Xylella fastidiosa (Xf), the causal bacterium of Pierce's disease, and leaf scorch in almond and oleander. Acquisition and inoculation of Xf occur sometime during the process of stylet penetration into the plant. That process is most rigorously studied via electrical penetration graph (EPG) monitoring of insect feeding. This study provides part of the crucial biological meanings that define the waveforms of each new insect species recorded by EPG. By synchronizing AC EPG waveforms with high-magnification video of H. coagulata stylet penetration in artifical diet, we correlated stylet activities with three previously described EPG pathway waveforms, A1, B1 and B2, as well as one ingestion waveform, C. Waveform A1 occured at the beginning of stylet penetration. This waveform was correlated with salivary sheath trunk formation, repetitive stylet movements involving retraction of both maxillary stylets and one mandibular stylet, extension of the stylet fascicle, and the fluttering-like movements of the maxillary stylet tips. Waveform B1 was ubitquious, interspersed throughout the other waveforms. B1 sub-type B1w was correlated with salivation followed by maxillary tip fluttering. This tip fluttering also occurred before and during B1 sub-type B1s, but was not directly correlated with either the occurrence or frequency of this waveform. Waveform B2 was correlated with sawing-like maxillary stylet movements, which usually occurred during salivary sheath branching. Waveform C was correlated with ingestion. Fluid outflow was also observed as a mechanism to clear the maxillary tips from debris during waveform C. This detailed understanding of stylet penetration behaviors of H. coagulata is an important step toward identifying the instant of bacterial inoculation which, in turn, will be applied to studies of disease epidemiology and development of host plant resistance.
玻璃翅叶蝉（Homalodisca coagulata (Say)）是木质部难养菌（Xylella fastidiosa, Xf）的高效传播媒介，Xf是桃叶穿孔病以及杏仁和夹竹桃叶焦病的致病细菌。Xf的获取和接种发生在口针穿透植物的过程中的某个时间点。该过程主要通过对昆虫取食进行电穿透图（EPG）监测来进行深入研究。本研究提供了部分关键生物学意义，这些意义定义了通过EPG记录的每种新昆虫物种的波形。通过将交流EPG波形与高倍视频同步，该视频展示了玻璃翅叶蝉口针在人工饲料中的穿透过程，我们将口针活动与之前描述的三种EPG途径波形A1、B1和B2以及一种取食波形C相关联。波形A1出现在口针穿透开始时。该波形与唾液鞘主干形成、涉及上颚口针和一个下颚口针回缩的重复性口针运动、口针束的伸展以及上颚口针尖端的类似颤动的运动相关。波形B1普遍存在，穿插于其他波形之中。B1亚型B1w与唾液分泌随后上颚尖端颤动相关。这种尖端颤动也发生在B1亚型B1s之前和期间，但与该波形的出现或频率没有直接关联。波形B2与类似锯切的上颚口针运动相关，这种运动通常发生在唾液鞘分支期间。波形C与取食相关。在波形C期间，还观察到液体流出是一种清除上颚尖端碎屑的机制。对玻璃翅叶蝉口针穿透行为的这种详细理解是朝着确定细菌接种时刻迈出的重要一步，这反过来将应用于疾病流行病学研究以及宿主植物抗性的开发。
