Landscape composition affects parasitoid body size in species-specific manner: A case study in Asian rice systems

Abstract

The top-down effect of natural enemies on pests is a crucial ecosystem service supporting integrated pest management. However, the variation in morphological traits of parasitoids in different landscape contexts and the differences in parasitoid emergence rate caused by this variation are still poorly known. We measured the inter-tegular distance (ITD) and body mass of three parasitoids– Cotesia chilonis (Munakata), Eriborus sinicus (Holmgren), and Microgaster russata Haliday – on overwintering larvae of Chilo suppressalis (Walker), the rice stem borer (RSB), collected from 20 rice paddies along a landscape heterogeneity gradient. Our objectives were to assess how landscape composition and landscape diversity affect functional traits (ITD and body mass) of species-specific parasitoid, and individual body size for its impact on biological control. From a total of 5002 sampled individuals of the three parasitoids, regression analysis revealed that (1) the presence of water bodies within the landscape respectively positive affected the ITD of E. sinicus and M. russata at 2000 m scales, landscape factors had yet no discernible effects on either the body size (ITD or body mass) of C. chilonis, (2) habitats with high landscape diversity had a negative effect on body size (ITD and body mass) of the solitary parasitoids E. sinicus at 200 m scales, and (3) a significantly negative correlation was found between the parasitoid emergence rate and ITD of E. sinicus. Our findings suggest that parasitoids’ body sizes may respond differently among species to landscape features. Solitary parasitoids in our study were more sensitive to variation in habitat resource-availability than was the gregarious parasitoid. We conclude that landscape habitat changes can affect the body size and parasitism of parasitoids, modifying their biocontrol services against pests.