Piercing and sucking behaviors monitoring
We monitored the HI lineage’s piercing and sucking behaviors on fresh
and pre-infected cucumber leaf using electrical penetration graph system
(EPG) (Tjallingii et a., 1988). Cucumber leaf and aphid were made parts
of an electrical circuit in this system. An electrode attached to a gold
wire (diameter 20 μm) was inserted into leaf petiole, and the other end
of the gold wire was attached to aphid dorsum using electric-conducting
glue. When the aphid started probing plant cells, the circuit was closed
and electrical signals generated. EGP signals (referred to as waveforms)
were the result of voltage fluctuations correlating to the stylet
locations within leaf mesophyll (Tjallingii and Esch 1993). Piercing and
sucking behaviors of 5-d-old aphids were monitored constantly for 6 h
under 22±2 °C. Three treatments were set: the HI lineage on fresh
cucumber (HI_fre_F1), the HI lineage on pre-infected cucumber
(HI_fre_F1) and the CU lineage on fresh cucumber (CU_fre_F1). Each
treatment replicated more than 10 successful recordings. Data were
analyzed by Stylet+a v1.25 software. Four typical waveforms were
analyzed: (1) C waveform,
reflecting stylet contacting with
the epidermis and penetrating epidermis and mesophyll cells, (2) G
waveform, reflecting active sap ingestion from xylem elements. When the
stylet reached plant phloem, two types of waveforms occur: (3) E1 and
(4) E2 waveform. E1 is often a short phase of stylet secreting saliva
into phloem element. E2 is the
phloem sap ingestion phase that
can last for hours or days on suitable host plants.