Objectives We investigated the chemical mechanism of how silicon decreases Sitobion avenae's host selection preference by studying the influence of silicon application on the release of wheat volatiles.

Methods A hydroponic wheat experiment was conducted using the wheat cultivar ‘Zhengmai 1036’ as a test crop, Sitobion avenae as the aphid, and Hoagland as a nutrient solution. The four treatments were no Si application and no aphid infestation (CK), only aphid infestation (A), only Si application (Si), and both Si application and aphid infestation (SiA). Si was sprayed on wheat seedlings at 2-open leaves-1-sprout and 3-open leaves-1-sprout stages. The aphids were infected on wheat leaves at the 5-leaves-1-sprout stage, with 30 aphids per pot. The Y-shaped olfactory instrument was used to test the host selection behavior of aphids. Wheat volatiles were collected using the headspace adsorption method, identified, and quantitatively determined using GC-MS. Principal component and correlation analyses were used to define the influence of volatiles on the host selection preference of aphids.

Results Si application led to a (P＜0.01) difference in wheat's tropism and repellency regardless of aphid infection. Aphids were more likely to choose wheat as a host when Si was not applied. Alkanes, benzenes, and alcohols were among the volatiles found in wheat. The number and concentrations of volatile chemicals in wheat were altered by Si treatment and aphid infection. Compared with A, SiA (P<0.05) increased the relative content of the volatiles dodecamethyl, 3-hexen-1-ol (E), and D-limonene by 56.25%, 112.00%, and 117.78%, respectively; the relative content of 2,4-dimethyl-heptane was (P<0.05) reduced by 81.02%. The principal component and correlation analysis results showed that the selection of the host by Sitobion avenae was (P<0.05) positively correlated with the volatile gas 2,4-dimethyl-heptane, and (P<0.05) negatively correlated with the volatile gas dodecamethyl, 3-hexen-1-ol (E) and D-limonene.

Conclusions Si application can enhance the repellency of host wheat to Sitobion avenae by increasing the release of wheat gas volatiles dodecamethyl, 3-hexen-1-ol (E) and D-limonene and decreasing the release of 2,4-dimethyl-heptane, which together impact the host selection of Sitobion avenae.