Future-proofing pastures from an insect sleeper pest

Tropical armyworm, Spodoptera litura (Lepidoptera: Noctuidae), has caused sporadic damage in Aotearoa New Zealand since its establishment in the 1970s. It is thought to be a ‘sleeper pest’ that is likely to become increasingly important due to predicted changes in climate, particularly increases in temperature. Larval S. litura are known to feed on hundreds of broad-leaf species worldwide but there are large gaps in our understanding of its host preferences in this country, especially with respect to agricultural pasture plants.

Plant species such as plantain, chicory, red clover and white clover are anticipated to increase in abundance in pasture swards in response to changes in climate and farming practice. We therefore assessed their suitability as host plants for S. litura by feeding individually caged larvae with known quantities of cut herbage from one of each plant species. Our results showed that larvae can complete development on all these species but food intake, growth and feeding efficiency varied between hosts. This variation can lengthen development time or decrease pupal bodyweight, and in turn affect female egg-laying. Plant host thus has intergenerational and population level implications for S. litura.

Our work seeks to identify useful plant species and fitness traits for future forages that are less vulnerable to S. litura, and to understand the potential genetic basis of these traits. Knowledge gained will provide an important basis for decision making around pasture planting under future climate change conditions, and for developing robust future forages.