Summary• The ability of the nematode-trapping fungus Arthrobotrys oligospora and the nematode egg parasite Verticillium chlamydosporium to colonize barley ( Hordeum vulgare ) and tomato ( Lycopersicum esculentum ) roots was examined, together with capability of the fungi to induce cell wall modifications in root cells.• Chemotropism was studied using an agar plate technique. Root colonization was investigated with light microscopy and scanning electron microscopy, while compounds involved in fungus-plant interactions were studied histochemically.• Only A. oligospora responded chemotropically to roots. Colonization of barley and tomato by both fungi involved appressoria to facilitate epidermis penetration. V. chlamydosporium colonized tomato root epidermis and produced chlamydospores. Papillae, appositions and lignitubers ensheathing hyphae on tomato were also found. Phenolics (including lignin), protein deposits and callose were present in papillae in both hosts. Both fungi were still present in epidermal cells 3months after inoculation.• Nematophagous fungi colonized endophytically monocotyledon and dicotyledon plant roots. Arthrobotrys oligospora seemed to be more aggressive than V. chlamydosporium on barley roots. Both fungi induced cell wall modifications, but these did not prevent growth. The response of root cells to colonization by nematophagous fungi may have profound implications in the performance of these organisms as biocontrol agents of plant parasitic nematodes.

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.

We have used Galleria mellonella (Linnaeus, 1758) larvae as a bait for detecting insect pathogens in soils from Alicante(SE Spain). Soil from 61 sites was collected including agricultural fields, forests and a mediterranean shrub(Nerium oleander L.) growing under natural or garden environments. The most frequently insect pathogens found werefungi (32.8% soils), being Beauveria bassiana (Bals.) Vuill (21% soils) the species most abundant. Metarhiziumanisopliae (Metschn.) Sorok (6.4%) and Lecanicillium lecanii (Zimm.) Gams [= Verticillium lecanii Zimm.] (4.8%)were less frequent. B. bassiana also scored the highest infection percentage in a single soil sample (ca. 90% of insectsinfected), and was also the most frequent (77.8%) entomopathogenic fungus detected in soils under N. oleander.

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