Evaluation of side effects of two Providencia entomophila strains associated with major olive tree insect pests on the parasitoid Trichogramma oleae

The control of olive tree insect pests has mostly been performed for several decades by chemical means. However, in an attempt to develop more natural treatments, two Providencia entomophila Ksentini et al. (Enterobacterales Morganellaceae) strains (IO-6 and IO-20) previously isolated from the olive tree insect pests Prays oleae Bernard (Lepidoptera Hyponomeutidae) and Bactrocera oleae (Rossi) (Diptera Tephritidae), respectively, were tested and were found to be effective against B. oleae. The side effects of both strains on beneficial insects were evaluated on the preimaginal stages and the adults of the egg parasitoid Trichogramma oleae Voegele et Pointel (Hymenoptera Trichogrammatidae) at concentrations ranging from 105 to 109 cfu/ml. The results showed that all IO-6 tested concentrations harmed T. oleae larvae, as well as the concentration 109 cfu/ml on prepupae. In contrast, different concentrations of strain IO-20 were found to be harmless for all developmental stages but slightly harmful at concentrations of 109 and 106 cfu/ml on larvae and prepupae, respectively. Nevertheless, none of the tested strains and concentrations were found to be persistent even 2 days after treatment application, as T. oleae adult survival was not negatively affected by any bacterial strain. However, when treatments were applied during developmental stages, some side effects on females external appearance, as brachypterous, two-male-antennae and single-male-antenna, were detected. Thus, taking into consideration all the aforementioned parameters, only P. entomophila IO-20 at a concentration of 105 cfu/ml guarantees perfect respect to all T. oleae developmental stages and offspring appearance.