Isolation, identification and pathogenicity of fungi isolated from mouthparts of coconut bug, Pseudotheraptus wayi Brown (Hemiptera: Coreidae) to litchis in South Africa

The coconut bug, Pseudotheraptus wayi, is a sap-feeding insect known to damage a wide range of host plants. Its feeding mechanism allows it to inject toxic saliva into plant tissue, and potentially, to transmit fungal pathogens. This study aimed to isolate and characterise fungal species associated with the coconut bug mouthparts, and to assess the pathogenicity of the fungal isolates on litchi fruits. A total of 29 fungal species were identified from 16 bugs. Morphological differences in colony colours, patterns and textures further distinguished these isolates. A total of 300 litchi fruits were inoculated with five fungal species, namely: Pestalotiopsis microspora, Xylaria sp., Nigrospora oryzae, Cladosporium cladosporioides, and Purpureocillium lilacinum. Three parameters (weight loss, colour change and disease severity) were assessed on the fruits over 14 days. The results indicated that the weight loss ranged from 21.58% to 18.67% and disease severity from very severe to slight. Pestalotiopsis microspore and Purpureocillium lilacinum were the pathogens with the most and least pathogenicity, respectively. These findings highlight the potential significant threat posed by fungal pathogens and emphasise the need to monitor and control the coconut bug to maintain litchi fruit quality and reduce post-harvest losses. Future research should explore the actual role and transmission dynamics in natural litchi–insect systems (field-based pathogenicity trials) to confirm the findings of this study.