Do opposing components of plant quality interact to influence feeding dynamics in the true armyworm, Pseudaletia unipuncta? A case for nitrogen and silicon

Background/Question/Methods

While increased nutrient availability can significantly enhance plant palatability and resource quality for herbivores, many plants employ physical defenses such as tissue silicification, which act to deter consumers and reduce plant digestibility. Little is known regarding how these opposing components of plant quality interact to influence patterns of herbivory, particularly in agroecosystems where extensive N application may substantially reduce the effects of defenses in silicon accumulators such as corn.  The aim of this study was to determine the effects of variation in leaf tissue quality on feeding dynamics in the true armyworm, Pseudaletia unipuncta. Nitrogen and silicon treatments were applied to corn plants in full factorial combination to quantify their interactive effects on insect diet choice and performance.

Results/Conclusions

Both feeding rate and larval development time were significantly reduced by silicon addition, while pupal weight was unaffected. Interestingly, when give a choice larvae preferred the low N diet, which may have resulted from a reduction in plant water content under the N fertilization treatment. Overall, we found that under no-choice feeding assays silicon addition had a substantial influence over armyworm feeding dynamics regardless of N application, and that when presented multiple diets, plant water content was likely an important determinant of feeding choice. Our findings suggest that nutrient addition has little influence over the effects of physical defenses such as silicon accumulation on the feeding dynamics of armyworm crop pests.