Host plant (Solanum carolinense L.) inbreeding affects larval growth, adult flight metabolism, and gene expression of a specialist herbivore (Manduca sexta L.)

Herbivores are challenged with a variety of plant produced physical and chemical defenses during leaf feeding. Therefore, holometabolous insects have the ability to fine-tune their growth and development in response to changes in host plant quality. Insects use this strategy to maximize growth and fitness during suboptimal feeding conditions. At the cellular level, alternative gene splicing is a key mechanism used by these insects to respond to their environment, via changes in the insect’s internal biochemistry. One factor hypothesized to affect the quality of a host plant is inbreeding. Inbreeding changes leaf volatile profiles and reduces trichome density compared to outbred plants. This suggests that inbreeding could alter a plant’s chemical and physical defenses making inbred plants more palatable to herbivores. We tested this hypothesis by rearing a specialist herbivore, Manduca sexta, on inbred and outbred Horsenettle (Solanum carolinense L.) plants. We measured different fitness parameters of the insects such as: larval growth, adult body size, adult flight metabolism, and the relative abundances of the longer isoforms (A & C) of Troponin t (Tnt), a thin filament regulatory complex expressed in insect flight muscle. Our results show larvae that fed on the inbred plants have improved growth, larger pupae size, and higher adult flight metabolism compared to larvae reared on outbred plants. This study demonstrates how natural variation in a host plant’s genetic background translates to observed changes in the morphology, physiology and behavior of a specialist insect herbivore.