Crop production in dependence of landscape complexity, herbivore density and plant tolerance

The transition from agricultural landscapes dominated by natural habitats to landscapes dominated by agricultural areas, has directly affected herbivore abundance and plant herbivore damage. Those changes in herbivory can have profound economical consequence in terms of crop production.  Compensatory plant responses to herbivore damage, decrease the negative effects imposed by herbivores on plants. However, the effect of plant compensatory responses to herbivory in landscapes differing in their complexity (i.e. percentage of natural areas) has not been explored. In one Colombian potato variety we previously found that plants attacked by low numbers of Guatemalan potato moth (T. solanivora) larvae produce a 2.5 fold higher marketable potato yield than undamaged plants, providing a model case of herbivore-mediated overcompensatory plant responses. Previous work also showed that landscape simplification (an increase in the percentage agricultural areas) increased potato moth density and decreased plant biomass. Here we wanted to assess if the induction of plant compensatory responses would decrease the negative impact of herbivore abundance on plant biomass caused by changes in landscape simplification. We chose 15 sites differing in the percentage of agricultural area and altitude where we set up plots of overcompensating plants and non-compensating plants under insecticide and non-insecticide treatments to quantify the effect of landscape simplification mediated through changes in herbivore abundance on plant biomass. As predicted landscape simplification increased potato moth abundance and the amount of plant tissue damaged by herbivores. Across all varieties and treatments, moth abundance had a negative effect on plant biomass.  In the compensating variety, plant biomass decreased more steeply in control plots than in insecticide-sprayed plots as moth abundance increased.  Despite the negative effect of moth abundance on plant biomass, the overall biomass of the compensating variety in control plots was greater than in insecticide-sprayed plots, while the non-compensating plants had a higher biomass in insecticide sprayed plots than in control plots. Our results show that counteracting the negative effects of landscape simplification on crop productivity has not an easy solution and that although plant tolerance can help maintain a higher overall biomass in the presence of herbivores, the negative effect of landscape simplification on plant biomass and therefore agricultural production is increased.