Abstract
We studied the role of plant primary and secondary metabolites in mediating plant-insect interactions by conducting a no-choice single-plant species field experiment to compare the suitability, enzyme activities, and gene expression of Oedaleus asiaticus grasshoppers feeding on four host and non-host plants with different chemical traits. O. asiaticus growth showed a positive relationship to food nutrition content and a negative relationship to secondary compounds content. Grasshopper amylase, chymotrypsin, and lipase activities were positively related to food starch, crude protein, and lipid content, respectively. Activity of cytochrome P450s, glutathione-S-transferase, and carboxylesterase were positively related to levels of secondary plant compounds. Gene expression of UDP-glucuronosyltransferase 2C1, cytochrome P450 6K1 were also positively related to secondary compounds content in the diet. Grasshoppers feeding on Artemisia frigida, a species with low nutrient content and a high level of secondary compounds, had reduced growth and digestive enzyme activity. They also had higher detoxification enzyme activity and gene expression compared to grasshoppers feeding on the grasses Cleistogenes squarrosa, Leymus chinensis, or Stipa krylovii. These results illustrated Oedaleus asiaticus adaptive responses to diet stress resulting from toxic chemicals, and support the hypothesis that nutritious food benefits insect growth, but plant secondary compounds are detrimental for insect growth.
Highlights
Half of all insect species are herbivores[1, 2]
The main chemical traits of three nutritive components and five secondary compounds for four food plants were measured by high performance liquid chromatography (HPLC)
We used single-plant no-choice field cage trials to compare the suitability of four plant species with different chemistry to O. asiaticus
Summary
Half of all insect species are herbivores[1, 2]. Co-adaptations between herbivorous insects and host plants have been studied in depth. The question of which selective factors have driven the evolution of host adaptability by insect herbivores is of great interest Ecological factors such as susceptibility to predation and aspects of habitat association are important in selection but plant chemistry is critical and includes nutrition, nutritional barriers, and secondary compounds[2, 11, 12]. Fecundity, fitness, and population levels usually increase when they feed on plants of optimal quality and low toxin concentrations[12, 31, 32] The availability of such plants may increase the probability of pest population outbreaks, whereas reduced access to key nutrients or increased levels of secondary compounds may have the opposite effect[14, 28]
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