Abstract
Insects infected with entomopathogenic fungi, experience physiological changes that influence their growth and immune defence. The potential of nine isolates of entomopathogenic fungi was evaluated after determining percent germination and relative conidial hydrophobicity. However, nutritional indices were evaluated after immersing eighth-instar Rhynchophorus ferrugineus larvae into each isolate suspension (1 × 107 conidia/mL). The results showed that isolates B6884 and M9374 had 44.51% and 39.02% higher conidial hydrophobicity compared with isolate I03011 (least virulent). The results of nutritional index assays revealed a significant reduction in growth indices after infection with different isolates. Compared with control, B6884 and M9374 greatly decreased larval growth by reducing the efficacy of conversion of ingested food (36%–47%) and Efficacy of conversion of digested food (50%–63%). Furthermore, only isolate B6884 induced 100% mortality within 12 days. Compared with control, isolate I03011, possessing the lowest conidial hydrophobicity, only reduced 0.29% of the efficacy of conversion of ingested food (ECI) and 0.48% of the efficacy of conversion of digested food (ECD). Similarly, transcriptomic analysis of genes related to the Red palm weevil (RPW) immune response, including pathogen recognition receptors (C-type lectin and endo-beta-1,4-glucanse), signal modulator (Serine protease-like protein), signal transductors (Calmodulin-like protein and EF-hand domain containing protein) and effectors (C-type lysozyme, Cathepsin L., Defensin-like protein, Serine carboxypeptidase, and Thaumatin-like protein), was significantly increased in larval samples infected with B6884 and M9374. These results suggest that for an isolate to be virulent, conidial hydrophobicity and germination should also be considered during pathogen selection, as these factors could significantly impact host growth and immune defence mechanisms.
Highlights
Red palm weevil (RPW) is an exotic highly destructive pest of palms, Phoenix dactylifera, in different geographical areas worldwide
Non-significant differences in conidial germination were observed among all the isolates, except I7284, B3H203, and I03011 (F = 97.3; df = 8, 36; p < 0.0001)
Results obtained from the virulence-determining traits evaluated in the current study enable us to suggest that germination percentage and relative conidial hydrophobicity significantly affect the virulence of the tested isolates
Summary
Red palm weevil (RPW) is an exotic highly destructive pest of palms, Phoenix dactylifera, in different geographical areas worldwide. The legless, creamy white larvae (grubs) of Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) are the most destructive stage of the weevil. These insects feed on tender soft palm tissues and move toward the centre of the infested host palm. The control of the RPW primarily relies on the frequent use of synthetic pesticides [1]. These practices are not sustainable, endanger biological diversity, and deteriorate environmental quality. These setbacks have led to the search for alternative methods of RPW control, bio-control agents. The initial step toward the development of mycoinsecticides should involve laboratory evaluation to grade the tested isolates in terms of virulence [9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
