An Agricultural Balancing Act:
A look at the biological control consequences of crop domestication
In terms of biological control, there are numerous top-down and bottom-up factors that play a role in the dynamic balance between plants and herbivores. Top-down factors are regulating mechanisms in which herbivore population numbers are controlled through upper trophic level organisms such as predators, natural enemies and parasitoids. In response to a lack of mobility, plants have developed an array of bottom-up mechanisms with which they can resist attack. Bottom-up controls are synergistically balanced with top-down controls in natural systems for overall suppression of herbivore populations. Plants utilize bottom-up mechanisms directly, through chemical and physical features used to resist damage and indirectly, by signaling to predators of an ongoing attack. These cries for help are in the form of volatiles (herbivore-induced plant volatiles, or HIPVs) that predators and parasitoids can respond to, finding food and reproductive hosts while simultaneously defending the plant. The HIPVs influence both bottom-up and top-down controls in this tri-trophic interaction.
Dr. Rodriguez-Saona seeks to understand these tri-trophic interactions with managed agricultural systems. He stresses that meaningful progress in pest management must include evaluation of human domestication as a factor influencing plant-mediated defense. Exploiting the availability of recently domesticated cranberry crop, its related varieties and its wildtype ancestor, Dr. Rodriguez-Saona was able to critically examine effects of domestication in a controlled setting. In a greenhouse study of five different cranberry varieties, Dr. Rodriguez-Saona applied a combination of jasmonic acid and gypsy moth caterpillars to investigate interactions between plant yield and the gypsy moth pest damage. He observed that the moth caterpillars did not perform as well on the jasmonic acid treated cranberries. This outcome was to be expected, as jasmonic acid is a signaling pathway that initiates plant defense in response to herbivore feeding. The five different cranberry varieties were then assessed for nutritional content, digestibility and HIPV production. He observed that bottom-up controls conferred through plant nutrition, digestibility, and HIPV production are altered by domestication as seen in the wild versus domesticated varieties (Rodriguez-Saona 2011b). Ultimately, bottom-up defense emanating from plants in hybridized/domesticated varieties were significantly reduced in the selection of higher yields with larger, more uniform fruit.
Kaplan, I. 2012. Attracting carnivorous arthropods with plant volatiles: The future of biocontrol or playing with fire? Biological Control 60(2): 77–89.
Rodriguez-Saona, C., Kaplan, I., Braasch, J., Chinnasamy, D., and Williams, L. 2011(a). Field responses of predaceous arthropods to methyl salicylate: A meta-analysis and case study in cranberries. Biological Control 59: 294-303.
Rodriguez-Saona, C., Vorsa, N., Singh, A., Johnson-Cicalese, J., Szendrei, Z., Mescher, M., and Frost, C.J. 2011(b). Tracing the history of plant traits under domestication in cranberries: potential consequences on anti-herbivore defenses. J. Exp. Bot. 62: 2633-2644.
Jessica is a master’s student in Dr. Lamp’s lab focusing in integrated pest management. She currently is working with kudzu bug’s cold tolerance in Maryland. For more on Jessica visit the Lamp Lab page.
Lauren is a master’s student in Cerruti R.R. Hooks’ lab who is conducting research on sustainable agricultural practices. She is currently studying effects of habitat manipulation as a pest control tactic in organically managed cropping systems.