Fig. 4

Role of salt-related PPKs during feeding. A Experimental design for feeding experiments. The feeding activity of four groups of insects was tested in the artificial feeder: uninjected, dsRNA-ctrl, dsRNA-Rproppk014276, and dsRNA-Rproppk28. The artificial feeder was connected to an electromyographic recording system, where the recording electrode was linked to a metallic mesh supporting the insect, and the reference electrode was immersed in the feeding solution. Once the insect inserted its mouthparts into the feeder, the electrical circuit closed, generating a base conductance. Changes in the baseline signal were attributed to contractions produced by the sucking muscles when the insect initiated feeding. Recorded signals were amplified, digitized, and stored in a PC. All four experimental groups were offered with a + NaCl/ + ATP solution. A control group of uninjected insects was tested with a − NaCl/ + ATP solution. B Example of electromyographic recordings of the muscles involved in feeding. Uninjected, dsRNA-ctrl and dsRNA-Rproppk28 groups exhibited similar responses to the + NaCl/ + ATP solution, showing a regular pumping behavior. In contrast, dsRNA-Rproppk014276 insects, when offered with + NaCl/ + ATP or uninjected insects offered with − NaCl/ + ATP solution, displayed low and scattered pumping activities relative to the other groups. C Pumping frequency during feeding of treated and uninjected insects on the + NaCl/ + ATP or − NaCl/ + ATP solutions. No differences were found between uninjected, dsRNA-ctrl and dsRNA-Rproppk28 groups. However, dsRNA-Rproppk014276 insects showed significantly lower frequency values than the other groups. Notably, the dsRNA-Rproppk014276 group offered with the appetitive solution + NaCl/ + ATP showed no differences from uninjected insects fed on − NaCl/ + ATP solution. Scatter plots are displayed, and bars represent the mean pumping frequency (mean ± s.e.m.). Asterisks indicate significant differences of each group to uninjected insects fed on the + NaCl/ + ATP solution (p < 0.001) (+ NaCl/ + ATP groups: uninjected, n = 14; dsRNA-ctrl, n = 15; dsRNA-Rproppk28, n = 19; dsRNA-Rproppk014276, n = 13; and − NaCl/ + ATP uninjected group, n = 10)