Egg Deposition of <i>Micromelalopha sieversi</i> (Staudinger) on Clones of <i>Populus</i> from Section <i>Aigeiros</i> Induces Resistance in Neighboring Plants

Research Highlights: We demonstrated that the resistance mechanisms of plants could be used to combat damage caused by pests in forestry plantations. Background and Objectives: Poplar is the main tree species used in plantations in northern China, with Micromelalopha sieversi (Staudinger) representing a major pest species causing defoliation. Here, we investigated whether two poplar clones could resist this pest species and the physiological mechanisms involved. Materials and Methods: Two clones of Populus from section Aigeiros were used, with &#8216;108&#8217; (P. &#215; euramericana &#8216;Guariento&#8217;) being more attractive to M. sieversi than &#8216;111&#8217; (P. &#215; euramericana &#8216;Bellotto&#8217;). Three treatments were set up (oviposited plants, neighboring plants, and control plants) to determine whether resistance was induced in plants neighboring oviposited plants. Results: Significantly fewer eggs were oviposited on neighboring plants compared to control plants for both clones, with more eggs being laid on oviposited and control plants of &#8216;108&#8217; compared to &#8216;111&#8217;. &#946;-Pinene was detected in oviposited and neighboring plants, but not control plants for either clone. Significantly higher concentrations of 3-carene was present in oviposited and neighboring plants of &#8216;108&#8217; and &#8216;111&#8217; compared to control plants at 24, 48, and 72 h after oviposition. Males, females, and mated females primarily responded to electroantennogram (EAG), methyl palmitate and 2-ethylhexyl acrylate at 50 ng/&#956;L, and to 3-carene and &#946;-pinene at 5 ng/&#956;L, and to styrene at 10 ng/&#956;L in EAG assays. When using these concentrations on plant leaves, 3-carene, &#946;-pinene, and styrene significantly reduced the number of eggs laid on &#8216;108&#8217;, while 3-carene and &#946;-pinene were effective for &#8216;111&#8217;. Conclusions: Plants neighboring oviposited plants exhibited defense responses; 3-carene and &#946;-pinene were used to transmit chemical signals (volatile cues) from oviposited plants to neighboring plants; which induced neighboring plants released volatiles as a defense mechanism to prevent egg laying