PMRC home PMRC home

news library expert forum links

Further Identification


Occluded insect viruses are the most commonly found viruses.
1. Use a bright field or phase contrast microscope.
2. You should see the characteristic shining white (mono-refringent) inclusion bodies.
3. Use stains such as Giemsa and Feulgen-Schiff to confirm presence of inclusion bodies.
4. Further identification of non-occluded viruses must be done using electron microscopy and serology techniques.


1. Before the insect decomposes, examine a drop of haemolymph under a phase contrast microscope.
2. If the bacteria are saprophytic you will see bacterial cells of different shapes and sizes.
3. If there are concentrations of bacilli-form cells this indicates the possible presence of an entomopathogenic bacterium.

N.B. Insect gut normally contains saprophytic bacteria. You must take care not to mistake these for disease-causing bacteria.

Bacillus thuringiensis: Good growth on nutrient agar, catalase positive, crystal parasporal body present.

Bacillus popilliae: Little or no growth on nutrient agar, catalase negative, crystal parasporal body usually present.

Bacillus sphaericus: Spores are almost spherical. No crystalline parasporal body.


Entomopathogenic fungi sporulate on the outside of the host insect under moist conditions and on the inside of the host when the environment is too dry.

Deuteromycete fungus: indicated by the presence of masses of powdery spores.
Beauveria spp.: white spores.
Metarhizium spp.: green spores.

Prominent hyphal structures, often brightly coloured: ascomycete (sexual stage) or an asexual genera e.g. Hirsutella.

Entomophthorales: stout hyaline hyphae surrounded by haloes of white spore deposits.

N.B. You must also use the microscope to confirm identification.


It is essential to differentiate between saprophytic gut protozoans (flagellates, amoebae) which are not pathogenic, and microsporal infections which are pathogenic.

To do this, use the Giemsa stain to pick out polar filaments extruding from the spore - these are Microsporidia.

Watch out for the type of locomotor organelle and the size and structure of the spores.


Mermithids: long, whitish, several times longer than the host.

Rhabiditid nematodes: small and accompanied by Xenorhabdus bacteria.

Heterorhabditis spp.: insect turns red.