Susceptibility of adult Exorista larvarum (Diptera Tachinidae) to conventional and transgenic Bacillus thuringiensis galleriae toxin

The tachinid Exorista larvarum is a polyphagous larval parasitoid of lepidopterans, including forest defoliators. Laboratory studies were conducted to investigate the side effects on adult parasitoid longevity and parasitization capacity of conventional and transgenic Bacillus thuringiensis galleriae (Btg) toxins, active against the pine processionary moth Thaumetopoea pityocampa and the wax moth Galleria mellonella. The flies were fed on lump sugar soaked with the bacterial suspensions and were thus treated by direct ingestion. In a first experiment, the Cry9Aa entomocidal toxin from Btg was administered at 3-times the dose to which the target lepidopterous species previously proved to be highly susceptible. E. larvarum male and female longevity from emergence and parasitization capacity (expressed as eggs/female laid on G. mellonella larvae and percentages of eggs which gave puparia) were not significantly affected by the treatment with the Cry9Aa toxin compared to a positive (the commercial Bt preparation Foray 48B) or to a negative (distilled water) control. No significant differences were also found between the two controls. In a second experiment, adult longevity and parasitization capacity were not significantly affected by the treatment with a suspension of the epiphytic bacterium Pseudomonas Clb01 carrying the cry9Aa Btg gene compared to wild type Pseudomonas or distilled water. These results indicate that E. larvarum adults were not affected either by the conventional or transgenic Btg Cry9Aa toxin according to the parameters and under the conditions tested. To complement this study, future investigations will have to be performed in a more realistic scenario than in a laboratory situation.