Infection of the Red Palm Weevil (Rhynchophorus ferrugineus) by the entomopathogenic fungus Beauveria bassiana: A SEM study

Abstract

The Red Palm Weevil (Rhynchophorus ferrugineus) is a devastating pest of palms in the Mediterranean, Middle East, and Eastern countries. No effective control measures are available. R. ferrugineus has been found naturally infected by the entomopathogenic fungus Beauveria bassiana, but its infection process in this host is unknown. We have studied the infection of R. ferrugineus larvae and adults by B. bassiana using dry conidia and conidia suspensions using scanning electron microscopy (SEM). In early stages, SEM revealed acquisition of B. bassiana conidia by cuticle ornamentation in legs, antennae, and elytra of R. ferrugineus adults. Subsequently, conidia germinated and frequent episodes of hyphal/conidial fusion were found. Appressoria, signs of adhesion and cuticle degradation led to penetration (even direct) and colonization of R. ferrugineus hosts by the fungus. B. bassiana conidiophores were found in a R. ferrugineus cuticle, which indicate the completion of the life cycle of the fungus in the insect host. SEM has proven that dry conidia of B. bassiana is an adequate inoculum for R. ferrugineus infection. SEM revealed that conidia of B. bassiana attached to the cuticle of R. ferrugineus can germinate and differentiate appressoria.

Effects of Combining Microbial and Chemical Insecticides on Mortality of the Pecan Weevil (Coleoptera: Curculionidae)

“…Since the insect cuticle does not provide nutrients to conidia of entomopathogenic fungi-but starves them and reduces germination (St. Leger et al 1992)-dry inocula should be more efficient for host penetration and infection. In fact, dry B. bassiana conidia performed better than conidial suspensions at degrading RPW cuticle and developing abundant infection structures such as appressoria (Güerri-Agulló et al 2010). …”

The electron microscopic examination of fungal distortions in the adult red flour beetle, Tribolium castaneum H. (Coleoptera: Tenebrionidae)

“…The insects were finally washed three times in a 100% acetone solution. The critical point drying using CO2 followed and the last stage of preparation was the gold-palladium coating for 120 s (Güerri-Agulló et al, 2010). The examination and photography were performed through a Joel Scanning Electron Microscope (JSM-T 330 A) equipped with image recording and processing system (Sem Afore).…”

Polymer/Layered Silicate Nanocomposite as Matrix for Bioinsecticide Formulation

“…These suspensions were filtered through sterile gauze to remove the mycelium and conidial concentration was determined in a Neubauer's chamber (hemocytometer) (New Optik, Brazil) using an optical microscope (MetrimpaxHungary/PZO-Labimex, Poland). [11,12] Suspension Viability The viability of the suspensions obtained was assessed by seeding 150 mL aliquots in Petri plates containing 5mL of PDA culture medium and incubating at 28 (AE1) C and 12-hour photophase. After a 17-hour period, the plates were withdrawn and the conidia observed with the aid of an optical microscope with a 40x objective.…”