Can symbiotic fungi protect plants from insect pests? A simple mathematical model

Abstract

A mathematical model is proposed for simulating and understanding the relationship between the potato plant and its most significant pest, the Colorado potato beetle, when mediated by mycorrhiza, a symbiotic plant-fungus association. From its analysis it is seen that, quite counterintuitively, an overabundant use of mycorrhiza for enhancing productivity is rather detrimental, in that it triggers persistent oscillations in the foliage and the population of the beetle, giving an instance of the paradox of enrichment. Some indications for biological pest control arise from the investigation of the bifurcations that occur in the model ecosystem. K E Y W O R D Sbifurcations, Colorado potato beetle, dynamical systems, mycorrhiza INTRODUCTIONThe Colorado potato beetle (CPB) originated from the south-west of North America, where it fed on plants of the genus Solanum in the family Solanaceae. It has now spread through most of North America, Europe, and Asia (especially Russia and China), feeding on the potato, Solanum tuberosum. The potato plant is native to the central Andes in South America, but is now an important and widely cultivated food crop. CPB is one of its most destructive and devastating insect pests. Chemical control has proven not to provide a long-term solution to the problems created by CPB, as the beetle has become resistant to a wide variety of chemicals. Biological control may represent a viable alternative. In this context, the use of mycorrhiza, a symbiotic association between the root of the plant and a fungus, has been advocated, as it shows interesting features. Mycorrhiza is indeed known to affect mineral composition of plants. 1 Mycorrhiza symbiosis influences several aspects of plant physiology: mineral nutrition uptake, plant growth, and plant resistance. 2-4 Among these we mention Ezio Venturino is a member of the INdAM research group GNCS.