Euwallacea Fornicatus (eichhoff, 1868) and Associated Novel Fungal Symbiont, Fusarium Sp.: A Potential Cause of Wilting in Cocoa, Theobroma Cacao in India

Cocoa is a commercially important beverage crop that faces new challenges in the context of climate change, which can alter pest and disease dynamics in cocoa plantations. In the Dakshina Kannada district of Karnataka, India, an abrupt increase in cocoa wilt was observed during the 2017-18 and 2018-19 periods. Systematic examination of affected trees revealed consistent attacks of Euwallacea fornicatus (Eichhoff, 1868; Coleoptera: Curculionidae: Scolytinae. In-depth studies of the wilted trees revealed the association of the plant pathogenic fungus Fusarium sp. with Euwallacea fornicatus. The identity of the obtained pure culture from the insect and infected tree was confirmed as Fusarium sp. using amplification of ribosomal DNA, RNA polymerase II largest subunit (RPB1) and translation elongation factor 1 (Tef1) genes. Notably, this study reports a remarkable case of mutualistic association between ambrosia beetles and Fusarium sp., belonging to the Fusarium solani species complex (FSSC), rather than the Ambrosia Fusarium clade (AFC). This finding highlights the intriguing diversity of mutualistic relationships in nature and sheds new light on the complex interactions between organisms. The present study also investigated the impact of rainfall on the colonization and spread of the Euwallacea-Fusarium complex. The findings revealed that rainfall was identified as a predisposing factor for the incidence and spread of attacks. Additionally, the study conducted a comprehensive analysis of the modeling of Euwallacea-Fusarium complex spread over a specific period of time.