PS 28-93 - Towards improved plant defenses in maize: how herbivory and flooding shape emitted plant volatiles and growth of fall armyworm

Background/Question/Methods

Flooding events are increasing in frequency and severity due to climate change, resulting in acute stress to plants. Devastation to crops is compounded when insect pests arrive. These combined stressors impact plants in various ways, reducing plant nutritional quality and altering production of Volatile Organic Compounds (VOCs). VOCs mediate a wide range of interactions between plants, insects and their natural enemies. To date, our understanding of how dual stressors of flooding and herbivory shape plant and insect interactions remains limited.

In our study, we examined the impact of flooding, herbivory, and their interactions on the emission of defensive plant chemistry and plant nutritional quality. We further evaluated how flooding-stress-induced plant changes may impact growth and performance of the destructive fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), an important insect pest of maize (Zea mays). Across five greenhouse studies, two hybrid maize varieties, conventional and organic, were exposed to three treatment groups: no flood control, flooded, and post-flood recovery (flooded seven days and allowed to recover). After seven days of flooding, one caterpillar per plant fed on leaves, and insect weighs were recorded every two days until pupation. Headspace VOCs and plant nutritional quality were collected from the final treatment group.

Results/Conclusions

Results showed caterpillars feeding on flooded conventional maize and non-flooded organic maize had the greatest weight gains. Results showed that combinatorial stressors affected the emissions of herbivore-induced VOCs in maize. Overall, 38 VOCs were identified in detectable quantities. As predicted, VOC emissions differed by variety, with the highest emissions of almost all compounds under combined stress (herbivory and flooding). The organic hybrid emitted larger quantities of VOCs than conventional hybrid. Flooding and herbivory influenced maize plant volatile emissions in variable ways. Our findings strongly suggest that combined abiotic and biotic stresses interactions impact plant quality and defensive chemistry with consequences for insect plant interactions as well as herbivore insect performance.

The implication of this finding should be considered particularly considering the looming climate crises, including flooding events and invasion of agricultural pests that will challenge our food supply. The focus on chemical ecology is crucial, as many herbivores and their natural enemies are known to use plant VOCs as host location cues. More understanding of these mechanisms could help lower the need for pesticide applications while improving yields and reducing insect damage to crop plants. This work is important because it could help identify novel approaches to pest management.