Host plant induced defenses affect larval growth parameters, adult flight metabolism, and gene expression of southern armyworm (Lepidoptera: Noctuidae)

Herbivores are challenged with a wide variety of physical and chemical plant defenses during leaf feeding. Previous studies found that plant produced protease inhibitors (PI) deter Lepidopteran larval leaf feeding behavior by interfering with a caterpillar’s ability to digest proteins, a critical dietary component. Holometabolous insects have the ability to fine-tune their growth and development in response to nutritional availability. At the cellular level, alternative gene splicing is a primary mechanism used by these insects to respond to variation in internal and external environmental conditions, via changes in the insect’s internal biochemistry. In this study, Southern Armyworm (Spodoptera eridania Stoll) larvae were allowed to complete their life cycle on wild type and mutant (Def1) tomato plants (Solanum lycopersicum L.). Def1 plants have a mutation in the Jasmonic Acid (JA) pathway that causes a reduction in their induced defensive production of PIs and other antinutritional proteins. We found that larvae reared on Def1 plants vs. wild type, showed a significant increase in larval growth parameters and development rate. In addition, the subsequent adult moths had greater body mass and improved flight metabolism, measured by peak CO₂ and total CO₂ output during adult flight activity. Lastly, the relative abundance of the longer isoforms (A & C) of Troponin t, a thin filament regulatory complex expressed in insect flight muscle, will be related to adult body mass, and flight metabolism. This study provides evidence that insect herbivores cope with environmental stressors, such as plant defensive chemicals, by tightly regulating body size and muscle growth.