Histopathological observations in the midgut and behaviour of olive fruit fly (Bactrocera oleae Gmelin) adults treated with a strain of Bacillus thuringiensis Berliner

Ultrastructural changes are usually observed in the midgut of various insect species after feeding on diets containing specific toxins from different Bacillus thuringiensis strains. A spore-crystal suspension of a Bacillus thuringiensis strain, previously known to be toxic against Olive Fruit Fly adults, was used to study the post-ingestion effects on the midgut ultrastructure of treated flies compared to untreated ones. Observations were carried out at different time intervals, until 72 h after feeding the bacterial suspension. Transmission electron micrographs showed a typical symptomathology involving a general disruption or disorganization of the midgut epithelial cells often ending in the cell lysis. Similar pathological changes in the intestine are known for other insect species belonging to the orders Lepidoptera, Coleoptera and Diptera. Behavioural observations were also carried out comparing treated to untreated flies. In the post feeding period, treated adults went through a progressive symptomatology which involved a general reduction in the activity, sluggish and shaky behaviour until general paralysis and death. The behavioural symptoms of intoxication paralleled the histopathology observed in the midgut of treated flies. Untreated adults looked healthy and did not show any pathological symptoms.