The notoriously destructive potato stalk borer (Trichobaris trinotata) has negligible impact on its native host, Solanum carolinense (horsenettle)

While herbivores can have a wide range of impacts on their host plants, instances in which herbivore damage is truly beneficial are rare. Thus, it was surprising that damage by the potato stalk borer (PSB) was associated with increased fitness of its native host plant (horsenettle) in a recent field study, particularly because this insect can have such severe negative effects on potato crops. A controlled experiment with potted horsenettle was conducted to investigate the impact of damage by PSB to see if it has any negative impacts on the plants, or whether horsenettle truly overcompensates for its damage. Damage by PSB had negligible impact on sexual reproduction and potential future vegetative propagation through root production in this experiment. Additionally, PSB damage did not exacerbate the negative fitness impact of heavy leaf damage by the eggplant lace bug. The lack of positive impacts in the potted horsenettle study suggests that selection for decreased resistance to PSB in the field study was due to correlated selection for increased plant vigor, rather than to overcompensation. That is, when given options, PSB females may preferentially oviposit on larger, healthier plants that are likely to be better hosts for their larvae. An important implication of these results is that a wild weed’s high tolerance of a natural herbivore can compound the weed’s potential to serve as a reservoir from which the herbivore can switch to closely related agricultural plants that are not tolerant of its damage.