Gypsy moth damage delays parasite attachment to cranberry hosts

Background/Question/Methods

Plants experience a myriad of interactions with other species that often occur sequentially. Herbivory may induce defenses involving jasmonic acid (JA) and salicylic acid (SA) signaling pathways that can directly affect preference and performance of subsequent herbivores, pathogens and even parasitic plants. Parasitic plants are present in most ecosystems, and can alter community dynamics and cause major economic damage in agricultural systems. For example, in heavily infested cranberry patches, the parasite dodder (Cuscuta sp.) can cause 80-100% yield loss. Although host plant nutritional quality can affect dodder foraging preference, the effects of herbivore damage to host plants on dodder preference remain unknown. Such information could potentially be used to simulate herbivory if previous herbivory confers resistance to dodder parasitism, offering producers an alternative management strategy for dodder control. Understanding how herbivore damage affects parasite preference also adds to our understanding of how single interactions structure subsequent community dynamics. Cultivated cranberry is genetically very similar or identical to native wild genotypes, making research with agricultural cultivars very relevant to understanding ecological interactions in native systems.

We conducted a greenhouse study to ask (1) Does gypsy moth damage (Lymantria dispar) affect subsequent dodder (Cuscuta pentagona) preference on cranberry hosts?  (2) Do cranberry cultivars differ in levels of phytohormones and phenolics, and does such variation correspond with dodder preference? and (3) Does gypsy moth damage induce phytohormones or phenolics in cranberry cultivars that may affect dodder preference? We used three cranberry cultivars: Mullica Queen, Stevens and Howes, to assess dodder preference. We measured dodder preference as the number of dodder stems attached and number of days to attachment.  In a separate experiment, we measured overall and induced chemical defenses for each cultivar, including phenolics and phytohormones, using HPLC and LC-MS/MS. 

Results/Conclusions

Gypsy moth damage reduced the number of dodder that attached by more than 50%, and also delayed attachment of dodder to cranberry host by approximately 2 days.  Cultivars varied in overall levels of some phenolics but not in phytohormone levels.  Gypsy moth damage marginally increased induced changes in the flavonol galactoside-3-quercetin, suggesting a possible mechanism of cranberry defense to dodder parasitism. These results indicate that a host plant’s single interaction with one herbivore species alters subsequent interactions with a prevalent parasitic plant, broadening our knowledge about community dynamics.