| dc.description.abstract | Agricultural intensification can reduce landscape complexity, leading to decreased biodiversity and pest control services in agricultural landscapes. One approach to address this issue is habitat manipulation through the introduction of refugia, such as flowering plants, into maize fields. Refugia can restore biodiversity and provide additional ecosystem services by attracting and supporting natural enemies. However, the effectiveness of habitat manipulation is strongly influenced by surrounding landscape conditions. This study aims to 1) analyze the effect of refugia and their distance from the field on the diversity and abundance of pests and natural enemies in maize crops, 2) examine the impact of refugia at the landscape scale on the diversity and abundance of natural enemies, as well as their effectiveness in suppressing pest populations, and 3) investigate the influence of refugia and landscape composition on the structure of pest-parasitoid food webs in maize crops.
This study was conducted in eight maize fields in Bogor. The fields were divided into two main treatment groups: four treated fields planted with refugia and four control fields without refugia. In the treated fields, three observation transects were established based on the distance from the refugia: 0, 10, and 20 m. Pest observation and natural enemy collection were performed in all fields at 2, 4, 6, and 8 weeks after maize planting. Natural enemies were collected using yellow traps and pitfall traps. Pests in the egg, larval, and pupal stages were collected directly from 100 maize plants. The pests are then reared in the laboratory to observe the occurrence of parasitization and the emergence of parasitoid imago. The collected insects and emerging parasitoids from the reared pests are being identified based on morphological characteristics to the morphospecies level. Landscape composition was determined using Sentinel-2 images processed using the Google Earth Engine cloud computing platform. The classification input consisted of a combination of the original bands, including bands 2, 3, 4, 5, 6, 7, 8, 8A, 11, and 12. The training sample included built-up land, water bodies, trees, rice fields, dryland agriculture, shrubs, and vacant land. The classification was carried out using a machine learning algorithm, specifically a random forest, and accuracy testing. The landscape parameters used were class area (CA) and the number of patches (NumP) for agricultural land and semi-natural habitats, as well as landscape shape index (LSI).
The study identified 42 insect pest families across six orders, 25 predator families across six orders, and 23 parasitoid families across two orders. No significant differences were observed in the abundance or richness of pests, predators, or parasitoids between the fields with and without refuge plants. The positive effects of refugia planting were observed in several groups of parasitoids, but their influence decreased significantly as the maize aged.
A significant negative correlation was found between distance from refugia and predator abundance and richness. Causality analysis indicated that higher predator abundance was associated with reduced pest abundance and richness. Additionally, while increased parasitoid abundance seemed to enhance the parasitization rates of Lepidoptera and Fall Armyworm, it did not correlate with increased parasitoid richness. These results underscore the challenges in farmland management in establishing suitable habitats for predators and parasitoids, ultimately enhancing natural pest control through ecological engineering practices.
This study found that at the landscape scale, planting refugia along maize field edges did not significantly increase the abundance or richness of parasitoids, nor did it increase predator richness. The landscape was relatively heterogeneous with more than 20% semi-natural habitat fragmented into small, dispersed patches separated by an extensive agricultural matrix. This structure appears to obscure the effect of refugia on boosting natural enemy populations, as natural enemy supply and movement are driven more by connectivity among patches than by local enrichment. Landscape variables such as the number of patches and the class area of semi-natural habitat negatively affected parasitoid abundance and richness, whereas semi-natural habitats positively affected predator abundance. Despite this complexity, refugia can increase pest parasitism even under complex landscape conditions. These findings highlight geographic variability in the amount of semi-natural habitat needed for effective local conservation. It is essential to consider refugia and semi-natural areas collectively to enhance pest control, and multi-year studies are needed to maximize the landscape-scale benefits of refugia.
Bipartite network analysis identified nine host morphospecies (Lepidoptera) in maize fields, with eight in fields without refugia and six in fields with refugia. Eight primary parasitoids were observed in both field types, with Paratetracnemoidea sp.1 and T. remus dominating fields without refugia, whereas T. remus was most prevalent in refugia-planted fields. Speices of S. frugiperda emerged as the primary host in both settings, with Paratetracnemoidea sp.1 and T. remus recognized as potential biological control agents. These results indicate that refugia can enhance food web metrics such as Shannon diversity and linkage density. Landscape structure and composition can mask the effects of refugia, resulting in simplified food chain structures as agricultural land areas increase. This study highlights the importance of landscape context in influencing plant-pest-parasitoid interactions, providing valuable insights for agricultural landscape management focused on natural enemy conservation and promoting sustainable pest control strategies. | |
