Cranberry plants produce volatiles when attacked by herbivorous insects, which can be used by beneficial insects, such as predators and parasitoids, to find food or hosts. Synthetic volatiles could potentially attract additional beneficial insects to cranberry fields, reducing insect damage and resulting in reduced yield losses. These volatiles could be used also to monitor the abundance of beneficial insects in agro-ecosystems.

At the P.E. Marucci Blueberry & Cranberry Research Center, a study by Drs. Elvira de Lange, Jordano Salamanca, James Polashock, and Cesar Rodriguez-Saona looked in detail at the emission of volatiles in different cranberry varieties (Figure 1), as well as the effects of synthetic volatiles on attraction of natural enemies of herbivores.

To study plant volatile emissions, we placed greenhouse-grown cranberry plants in bags, and sucked air out of the bags with small pumps (Figure 2). The air passed through a trapping filter with an adsorbent material, trapping the volatiles. Analysis revealed that volatile emissions in response to herbivory differed among cranberry genotypes. At the molecular level, we studied the expression of genes that are involved in the biosynthesis of these volatiles. We harvested leaf material, and found that the expression of two genes associated with volatile biosynthesis did not differ among the cranberry genotypes. These results indicate that other, not yet identified, genes may play a role in regulating volatile emissions in cranberry plants.

In the field, we placed yellow sticky traps (Figure 3), with or without a vial containing synthetic volatiles. We found that the volatile methyl salicylate, alone or in combination with other volatiles, increased the number of syrphid flies captured on the sticky traps by 6-fold. However, methyl salicylate repelled some natural enemies (i.e., megaspilid wasps). Similarly, the volatile

Figure 1. Cranberry genotypes

(Z)-3-hexenyl acetate repelled ladybeetles. Thus, the responses of natural enemies to synthetic volatiles in cranberry beds varied from repellency to attraction.

Experimentally changing plant volatile emissions may have some positive effects on biological control by attracting natural enemies, but can also have some serious negative consequences. Not only beneficial insects could be attracted, but herbivorous insects could be attracted as well. Also, certain natural enemies could be repelled. There is a possibility that when volatiles are present, but prey or hosts are absent, natural enemies learn to stop responding to the presence of volatiles. Our results indicate that, when practiced with care, synthetic volatiles may contribute to sustainable pest management practices in cranberry through the monitoring and recruitment of desirable natural enemies.

Figure 2. Volatile collection apparatus

This study is published in the Journal of Chemical Ecology: https://doi.org/10.1007/s10886-018-1043-0.

We thank technicians Vera Kyryczenko-Roth, Rob Holdcraft, and Kristy Adams, as well as the summer students in 2014 and 2015, for assistance with the experiments. Funding was provided by Hatch Project No. NJ08192 and the New Jersey Blueberry and Cranberry Research Council Inc., Cranberry Institute, Cape Cod Cranberry Growers Association, Canadian Cranberry Growers Coalition, and Ocean Spray Cranberries, Inc.

Figure 3. Sticky trap baited with synthetic volatiles