D3299: Exploring how landscape simplification influences plant defensive strategies as mediated by shifts in herbivore populations

As populations rise, so does agricultural demand, driving the continued conversion of natural landscapes to agriculture, also known as landscape simplification. While prior research has demonstrated that simplified landscapes are associated with decreased pollinator abundance and diversity, trends for herbivorous insects have been less predictable. When looking at herbivorous insect damage inflicted on the wild cruciferous plant Barbarea vulgaris, preliminary field surveys found that plants from complex landscapes incurred significantly greater damage than those from simple landscapes. This suggests that wild plants may experience differential herbivore pressure in simple versus complex landscapes, potentially driving changes in plant defensive strategies. Here we explored how wild plant defensive strategies were affected by landscape mediated shifts in herbivore populations, investigating the inducibility of two defensive secondary metabolites, glucosinolates and saponins. We hypothesized that there would be greater inducibility of secondary metabolites in simple landscapes where less herbivore damage was observed, while in complex landscapes, where herbivore pressure is high, we expected greater expression of constitutive defenses. We conducted a choice bioassay using Phyllotreta cruciferae and an HPLC-MS analysis to evaluate both insect choice and plant defenses. When comparing choice in uninduced simple and complex plants, P. cruciferae showed a preference for plants from simple landscapes, yet unexpectedly there was no difference in glucosinolates and saponin levels between landscape types. Next steps include investigating what else could be influencing herbivore choice, such as physical defenses or other chemical defenses not considered here.