Evaluation of Mediterranean fruit fly (Ceratitis capitata) host preference and metabolomics changes under acid-base stress to understand the biological and physiological changes

Rongrong Shi

doi:10.60867/00000087

Mediterranean fruit fly, Ceratitis capitata (Medfly), is one of the most devastating polyphagous pest species due to its broad host range and adaptability. Chemical control is still the dominant method in Medfly management, but strict regulations have banned the use of many insecticides in agriculture. A more comprehensive understanding of Medfly physiology, biology, and ecology is required to inform and develop alternative Medfly management strategies. This research project focused on understanding how the internal stages of the Medfly life respond to different acid-base conditions. Several studies have examined the development of larval instars under different pH conditions, but little is known about their limits under acid-base stress. This study indicated that Medfly eggs are the most tolerant internal life stage under extremely acidic and alkaline stress conditions, they can survive a short time treatment (10 minutes) with HCl (10 M) and NaOH (10 M) solution treatment. Our finding that Medfly eggs are the most tolerant stage to both acidic and alkaline stress can guide Medfly management. All Medfly internal life stages (eggs and larval stages) are more tolerant to alkaline (NaOH) stress compared to acidic (HCl) stress. Acid–base treatments significantly reduced overall survival but did not affect sex ratios, indicating equal tolerance between males and females. Under different acid-base conditional stresses, Medfly demonstrated significant changes in metabolic profiles. Body fatty acid content was significantly downregulated after Medfly received a highly acidic (10 M) treatment. The affected fatty acids are antibacterial fatty acids, which are the primary contributors to Medfly mortality. The antibacterial fatty acids included palmitoleic acid, n-hexadecanoic acid, and 9,12-octadecadienoic acid (Z, Z)-. Metabolic composition was further influenced by saturated salt treatments and host fruit species, with larvae fed on less acidic fruits exhibiting reduced fatty acid content. Medfly from different host fruits had significantly different metabolite profiles. Key compounds produced by larvae from the infested host fruit could serve as Medfly infestation markers to support quarantine inspection. This study demonstrated that host preference lacks a positive correlation between larval performance and adult Medfly survival. The old saying “mother knows best” does not always hold true. For example, eggs laid in a pear fruit hatched, but the 1st and 2nd instar larvae all drowned inside the host, indicating poor host choice by the mother. Host preference is affected by many factors, some of which are poorly understood, and this field deserves much greater investment in the future. Moreover, several identified compounds from infested host fruit, such as ethyl acetate, D-limonene and α-copaene, have promising potential insecticidal value. Overall, this thesis demonstrates the exceptional physiological resilience of Medfly to extreme acid-base tolerance and elucidates metabolic and chemical ecology mechanisms underlying its adaptability. This thesis paves the way for developing new methods by studying the basic physiological and biochemical and acid-base relations and impacts on different internal stages of Medfly. This thesis advanced our understanding of Medfly physiology and highlight novel opportunities for developing targeted, sustainable, and environmentally friendly pest management strategies.

Evaluation of Mediterranean fruit fly (Ceratitis capitata) host preference and metabolomics changes under acid-base stress to understand the biological and physiological changes

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