The foliar trichomes of horsenettle damage the peritrophic membrane of Manduca sexta larvae and negatively affect their consumption and growth rates

Previous studies have shown that inbred horsenettle plants produce fewer stellate trichomes constitutively than outbred plants and that the ability to induce additional trichomes upon herbivore damage is compromised in inbred plants. Consequently, we examined the effects of trichomes on the on the foliar consumption rate and growth rate of Manduca sexta larvae and we examined the impacts of foliar trichomes on the peritrophic membrane of larvae after consuming horsenettle leaves. We found that first instar larvae took longer to take their first bite and grew more slowly on the leaves of outbred plants that had higher trichome density. In a series of experiments in which larvae were given leaf discs in which the trichomes had been removed (shaved off) or unshaved we found that there was no difference in the consumption or growth rates of larvae on shaved leaf discs of inbred and outbred plants; that larvae consumed more and grew faster on shaved leaf discs compared to unshaved discs and on unshaved inbred leaf discs compared to unshaved outbred leaf discs. When we added the shaved trichomes to artificial diet, we found that larval mortality was greater and growth rates were reduced on diet containing the shaved trichomes. Finally, light microscopy and SEM revealed that foliar trichomes damaged the peritrophic membrane of 3^rd instar larvae which could alter digestion, nutrient absorption, and potentially expose the larvae to pathogenic microbes in the gut.  This is one of the few studies to demonstrate that non-glandular trichomes function to deter chewing insects.