Thirsty plant calling for help: Impact of drought on the ability of plant to attract enemies of plant-feeding insect

In many cases, plant attracts natural enemies of plant-feeding insect when attacked by these insects to defend themselves. This phenomenon is mediated through the emission of specific plant volatile compounds indicating the status of attack (i.e. plant crying for help). Natural enemies that feed on these plant-feeding insects are able to identify these scents and locate plant-feeding insects efficiently, which keep the plant-feeding insect in check. The successful perception and attraction of natural enemies in often very important in agricultural system where plant-feeding insect could lead to tremendous loss.

However, the emission and production of plant volatile is known to be sensitive to environmental changes, such as light, temperature, water availability etc. Since environmental stress such as drought is predicted to increase during the next decades because of current climate change regime, it is important to understand how drought affects the interaction between plant, plant-feeding insect, and their natural enemies. By conducting controlled field experiment in Taiwan and Japan, Po-An aims to understand the basic biology of such interaction and unravel unknown phenomenon that could not be detected in lab settings.

A crucifer weed, Rorippa indica, commonly grows in the field of Taiwan and Japan; cabbage white butterfly, Pieris rapae, that feed on R. indica were selected as the study system. In contrary to the former believes that drought stressed plant is bad for plant-feeding insect, Po found that drought stress of R. indica has an unexpected impact on the survival of cabbage white butterfly, which is mediated through the change in natural enemy diversity and abundance between well-watered and drought stressed R. indica. Detail analysis of volatiles emitted by plant under different water status will be conducted in Penn State University after the end of field work in October.

So far it seems that when plant are thirsty, the ability for them to call for help was also compromised and in some aspect beneficial for plant-feeding insects. However, more studies are required to unravel the underlying mechanisms.

*This collaborative project is partially supported by INTAD competitive research grant, Dr. Chuan-Kai Ho (National Taiwan university), and Dr. Natsuko Kinoshita (University of Tsukuba).

Article submitted by Po-An Lin.