Diversity of stink bugs (Pentatomidae) and associated egg parasitoids in macadamia orchards in South Africa

Abstract

The aim of this dissertation was to synthesise information on stink bug diversity and their associated wasp egg parasitoids, with a focus on the species present in macadamia orchards in South Africa. The work presented in this dissertation includes an overview of the diversity, importance and management of stink bugs associated with nut crops. A survey in which the diversity of stink bug species present in macadamia orchards was determined over three seasons in Limpopo (2017-2020) and one season (2019-2020) in KwaZulu-Natal and Mpumalanga was also conducted. This included a phylogenetic analysis of these species and other closely related species and/or species previously associated with nut crops, a sequence divergence analysis and the development of a mtDNA cytochrome c oxidase subunit 1 (COI) sequence and DNA database linked to morphology. Finally, a survey to identify wasp parasitoids parasitizing Bathycoelia distincta eggs in the Limpopo province and the testing two different molecular diagnostic approaches to identify these parasitoids was also conducted. Based on available literature, at least 19 Pentatomidae species have been associated with nut crops worldwide, with five species commonly associated with macadamia specifically in South Africa. Barcoding gene sequence availability on online databases is lacking for many of these species. The macadamia industry requires the implementation of effective integrated pest management (IPM) strategies and a reduction in yield loss due to stink bug damage to accomplish long-term sustainability. Successfully implementing strategies such as biological control using parasitoid wasps requires accurate identification of the stink bugs and their native parasitoids. A total of 20 stink bug species were identified across all three growing regions in this study and COI sequences for 16 of these species were made newly available on online databases. Bathycoelia distincta was the dominant species in all three regions and Boerias spp. were also found to be dominant in KwaZulu-Natal. Sequence divergence analysis confirmed the presence of cryptic species in the Boerias spp. and Pseudatleus raptorius groups. This is the first report of Boerias spp. on macadamia. The novel association of these species with macadamia and the fluctuation in species presence, both over time and across growing regions, highlights the need for ongoing monitoring of these pests. Monitoring will allow for the implementation of species-specific IPM strategies, ultimately leading to a reduction in the use of broad - spectrum insecticides. Monitoring relies on accurate pest identification and the COI DNA, sequence and photo database developed in this study will assist in future identifications. Based on a COI DNA barcoding approach, two native wasp parasitoids parasitizing B. distincta eggs in Limpopo were identified as Psix striaticeps and Trissolcus sp. Family-specific primers to analyze unemerged parasitized eggs were tested against COI primers for emerged adult parasitoids to determine the best method for identification. The COI sequencing using the standard primers on emerged parasitoids was deemed the most reliable approach. Future work should focus on the impact and management of the Boerias spp. in KwaZulu-Natal, include surveys to determine parasitoid species presence in other growing regions and assess the effectiveness of native parasitoids as biological control agents of stink bugs.