Comparison of the life history of a native insect Laelia coenosa with a native plant Phragmites australis and an invasive plant Spartina alterniflora

The invasion of Spartina alterniflora into saltmarsh ecosystems has resulted in a host transfer of a native generalist insect, Laelia coenosa. Currently, the life history of L. coenosa on S. alterniflora is unclear, although this information is of great importance for evaluating if the native insect can permanently use S. alterniflora. To compare the differences in life history dynamics of L. coenosa between its native host plant Phragmites australis and the invasive host plant S. alterniflora, we investigated the insect occurrence on the two plant habitats in a saltmarsh of the Yangtze River estuary in Chongming, Shanghai. We found that the insect occurred in three generations and overwintered as larvae on both S. alterniflora and P. australis. The larvae started overwintering about 20 days later on the invasive plant than on the native plant, and emerging duration of the insect at most stages of other generations was also approximately 10 days later on the invasive than on native plant. These results suggest that following S. alterniflora invasion the duration of the moth's appearance on the invasive plant is prolonged however the number of annual generations does not change. We speculate that the differences in growth and development of L. coenosa between S. alterniflora and P. australis may be related to resource availability between plant habitats and the nutritional and defensive levels between plant species.