Genotypic variation and phenotypic plasticity in gene expression and emissions of herbivore-induced volatiles, and their potential tritrophic implications, in cranberries

Authors: DELANGE, ELVIRA - University Of California, Davis; SALAMANCA, JORDANO - National Center For Agriculture And Forestry Technologies (CENTA); Polashock, James; RODRIGUEZ-SAONA, CESAR - Rutgers University

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2018
Publication Date: 1/3/2019
Citation: Delange, E.S., Salamanca, J., Polashock, J.J., Rodriguez-Saona, C. 2019. Genotypic variation and phenotypic plasticity in gene expression and emissions of herbivore-induced volatiles, and their potential tritrophic implications, in cranberries. Journal of Chemical Ecology. 45(3):298-312. https://doi.org/10.1007/s10886-018-1043-0.
DOI: https://doi.org/10.1007/s10886-018-1043-0

Interpretive Summary: Plant-eating insects pose a threat to cranberry production. Use of chemical pesticides is effective for control, but non-target insects are also impacted. Some of the non-target insects are beneficial as they prey on or parasitize the plant-eating insects. Therefore, we studied cranberry-produced chemicals that might attract beneficial insects. Attraction of beneficial insects to prey on the plant-eating insects may reduce the need for chemical pesticides. In a greenhouse, we tested nine different cranberry varieties for production of chemical attractants. In an experimental field, we tested whether baiting insect traps with potential chemical attractants would bring in beneficial insects. The results showed that different cranberry varieties vary in the chemicals they produce. Some of those were tested for their ability to attract beneficial insects. While some were found to be good attractants, others were found that were repellent. Understanding how to augment natural plant defenses, may contribute to the development of more sustainable pest management practices in crops, including cranberries. The information presented will be useful to scientists that study the plant chemicals that impact insect behavior.

Technical Abstract: Herbivorous insects are an important problem in cranberry (Vaccinium macrocarpon Ait.) production. Use of chemical pesticides is common practice, but beneficial insects such as the natural enemies of herbivores (e.g. predators and parasitoids) could be affected as well. Therefore, we studied the defensive mechanisms that cranberry plants themselves use to combat insect pests, focusing on herbivore-induced plant volatiles (HIPVs), which can be used by predators and parasitoids foraging for prey or hosts. Then, we used synthetic HIPVs to test the attraction of natural enemies. In a greenhouse, we assessed nine different cranberry genotypes for constitutive and induced expression of genes involved in HIPV biosynthesis and/or emission of HIPVs. In an experimental field, we assessed whether baiting traps with individual HIPVs or combinations of these HIPVs increased attractiveness to natural enemies. The results showed that different cranberry genotypes vary in their emission of monoterpenes and sesquiterpenes but not in their expression of two genes associated with terpene biosynthesis. Induction with methyl jasmonate (MeJA) or herbivore (i.e., gypsy moth) feeding increased expression of these terpene-related genes and emission of HIPVs. The HIPV methyl salicylate (MeSA) increased attraction of syrphids in the field by 6-fold, when alone or in combination with other HIPVs, while (Z)-3-hexenyl acetate and MeSA repelled ladybeetles and megaspilid wasps, respectively. Linalool and ß-caryophyllene had no effects on natural enemies. Elucidating mechanisms of pest resistance, as well as experimentally augmenting plant defenses like HIPVs, may contribute to the development of more sustainable pest management practices in crops, including cranberries.