The effectiveness of plant volatile defenses against insect herbivores

Abstract

Love it or hate it, a signature fragrance of summertime is the scent of a freshly mowed lawn, but that scent is much more than just a lovely bouquet of chemicals released by cutting the grass. When plants are attacked by insects or damaged by other means, they emit a variety of airborne volatile chemicals, or "volatiles" for short, which induce chemical defenses in leaves and roots, signal neighboring plants to pre-emptively initiate their defenses (called "priming" for defense), and attract predators and parasitoids that attack the insect herbivores. However, increased volatile concentrations within a field may also signal the presence of suitable hosts and attract herbivores that specialize on these plants. We have developed two mathematical models of the interactions between goldenrod (Solidago altissima) and one of its insect enemies to explore how plant defense strategies and herbivore behavior influence important components of fitness (reproductive success) of plants in a simulated field over a single month and over a full growing season. Using these models, we have been able to determine reasonable ranges of volatile emission rates for deterring insect herbivores. We have also determined that plant priming for defense is not always effective, which has led to further investigation of the range of conditions under which priming for defenses can reduce herbivore damage. We have also investigated the effects of variable wind speed and direction on the dispersal of volatiles through the field, the effectiveness of priming, and the spatial dynamics resulting from plant-herbivore interactions.