Impact of conservation landscapes on the abundance of insect pests and their respective natural enemies adjacent to citrus orchards

Abstract

Citrus is globally considered one of the most important fruit crops that is valued for both its economic contribution and nutritional value. South Africa stands as of the world's leading exporters of citrus, but the citrus industry in the country continues to face challenges from pathogens, insect pests, and increasingly strict phytosanitary regulations. These challenges have forced growers to adopt more intensive chemical spray programs, which endangers the long-term stability of ecosystems and beneficial arthropods within citrus agroecosystems. Recently, conservation landscapes, which are natural habitat areas within or around cropped lands, have gained attention as a possible way to boost natural enemies’ populations and lessen farmers' reliance on chemical control, offering the potential to improve wide-scale integrated pest management (IPM). This study investigated how these conservation landscapes adjacent to citrus orchards influenced adult false codling moth (FCM) populations and natural enemies of its pupal stage. In Chapter 2 of this thesis, we examined the spatial and temporal distribution of FCM across natural–orchard gradients and within an orchard system. The results showed that FCM populations were concentrated within orchard interiors, and their reproduction was strongly influenced by temperature variation, highlighting the important influence that climatic factors have on population fluctuations of this pest. Chapter 3 examined how proximity to adjacent natural habitats impacted the abundance of ground-dwelling predatory arthropods and whether increased abundance resulted in increased predation of FCM pupae. This was conducted across four citrus farms with different chemical input intensities. Predator abundance was assessed through pitfall trapping, and pupal baiting was used to see predation rates in relation to predator abundance, landscape configuration and chemical input. Our findings showed that the abundance of predators and pupal predation increased with proximity to natural habitats and were highest within orchards that had reduced chemical inputs, suggesting that natural vegetation and lower pesticide use enhance biological control potential. Overall, the results presented in this thesis demonstrate that maintaining and integrating conservation landscapes into citrus production systems can promote beneficial arthropod activity and support sustainable pest control in South African citrus agroecosystems, potentially lowering the need for heavy chemical input.