Effects of insect herbivory on phytoestrogen concentrations in three Trifolium species

Abstract Phytoestrogens are plant-produced secondary compounds believed to play a protective role against environmental stress. When consumed by animals, phytoestrogens can influence animal health and reproductive function; hence, there is interest in identifying factors that trigger their production in agricultural crops. We conducted two experiments to determine if leaf tissue herbivory by corn earworm ( Helicoverpa zea Boddie) induces phytoestrogen accumulation in three clover species commonly utilized as livestock forage. In experiment I, insects were fed on red clover ( Trifolium pratense L.) and kura clover ( T. ambiguum L.) for 7 days. Herbivory increased total phytoestrogen levels by 112% in red clover, while levels in kura clover were extremely low and not influenced by herbivory. In experiment II, herbivory was applied to two red clover cultivars and one white clover cultivar ( T. repens L.) for 9 days followed by a 9-day recovery period or for 18 days without recovery. After 9 days of herbivory and a 9-day recovery period, total phytoestrogen levels in red clover increased by 84%. Compared to the control, there were no differences in total phytoestrogen concentration when herbivory was applied to red clover for 18 days; however, additional sampling revealed concentrations were over 112% higher in undamaged compared to insect damaged tissues. Herbivory did not influence total phytoestrogen concentrations in white clover. These findings highlight the role insect herbivory can play in modifying the phytoestrogen status of red clover, and therefore a potentially novel mechanism by which insect herbivory may indirectly influence agricultural livestock health and reproductive function.