Microbial population and diversity on the exoskeletons of four insect species associated with gorse (Ulex europaeus L.)

Fungi and bacteria on the external surfaces of four gorse-associated insect species: gorse seed weevil Apion ulicis Forster (Coleoptera: Apionidae), light brown apple moth Epiphyas postvittana Walker.(Lepidoptera: Tortricidae), gorse pod moth Cydia ulicetana Denis and Schiffermuller (Lepidoptera: Tortricidae) and gorse thrips Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), were recovered by washing and plating techniques. The isolates were identified by morphology and polymerase chain reaction (PCR) restriction fragment length polymorphism and sequencing of internally transcribed spacer (ITS) and 16S rDNA. A culture-independent technique (direct PCR) was also used to assess fungal diversity by direct amplification of ITS sequences from the washings of the insects. All insect species carried Alternaria, Cladosporium, Corallomycetella, Penicillium, Phoma, Pseudozyma spp. and entomopathogens. Ninety-four per cent of the 178 cloned amplicons had ITS sequence similarity to Nectria inauritiicola (syn. Corallomycetella repens). E. postvittana carried the largest fungal spores (spore mean surface area of 126 mu m(2)) and the most fungal colony forming units per insect. Methylobacterium aquaticum and Pseudomonas lutea were isolated from all four insect species. P. fluorescens was the most abundant bacterium on the lepidopteran insects. This study presents the diversity of microbial taxa on insect exoskeletons, and provides the basis for developing a novel mycoherbicide delivery strategy for biological control of gorse using insects as vectors of a plant pathogen.