Impact of traditional pesticides and new controlled release formulations on Drosophila suzukii

The spotted wing drosophila, Drosophila suzukii, has become a great threat to European and American producton of soft and stone fruits. Laboratory and field experiments were performed to identify and optimize effective strategies to protect fruit crops from D. suzukii. The first experiment aimed at identification of the efficacy of most commonly insecticides used in Italy to control D. suzukii on cherries. As well as different chemical control strategies applied at commercial cherry orchards in Verona province, North-Eastern Italy, during the growing seasons of 2013, 2014 and 2015 were carried out to determine whether insecticide-based management programs and their timing can provide sufficient crop protection. Moreover, the adherence of those applied pesticides to their maximum residue levels’ (MRLs) requirements set in legal EU regulation for the marketed products was measured. Pre-treating cherries bioassay results revealed that pyrethroids (lambda-cyhalothrin, deltamethrin), spinosyns (spinosad, spinetoram), organophosphates (phosmet, dimethoate) and diamide (cyantraniliprole) were highly efficious, resulting in excellent (>90%) adult D. suzukii mortalities. Moreover, they were able to significantly suppress female fecundity, eggs laying and hatching, immature stages development, and adult emerging as well. Conversely, neonicotinoids (acetamiprid, thiamethoxam, thiacloprid, imidacloprid), Beauveria bassiana, and emamectin-benzoate caused unsatisfactory results. However, dipping infested-cherries bioassays suggested that cyantraniliprole, dimethoate and phosmet (Spada® WDG) can providemore than 10 days residual control for cherries. They caused complete activity, suppressing eggs hatching into larvae. Spinetoram and phosmet (Spada® 200 EC) provided good residual control. While, neonicotinoids (acetamiprid, thiamethoxam, thiacloprid), emamectin-benzoate and pyrethroids (lambda-cyhalothrin, deltamethrin) caused moderate impacts. Moreover, field results proved that two or three insecticide applications were insignificantly able to protect major cherry crops during three consecutive seasons of 2013, 2014 and 2015. Thus, effective D. suzukii control program can be achieved by timely of four applications of insecticides belonging different mode-of-action chemical groups. Except for dimethoate, all residue levels detected in cherries were lower than and completely adherence to their MRLs in force the European Union. It can be concluded that, spinosyns, diamides, organophosphates and pyrethroids may have an important role to protect cherry crop. Neonicotinoids and Beauveria bassiana suggested insignificant activities. The second experiment identified the efficacy of most commonly insecticides registered in Italy against D. suzukii on strawberries. An open field trial at a commercial strawberry orchard in Verona province, North-Eastern Italy in 2014, and two laboratory bioassay trials in March and September 2015 were performed to determine whether chemical control strategy can provide significant crop protection from D. suzukii. All strategies applied in the field trial significantly succeeded to decrease the damage of strawberries compared to the untreated plants either at 14 or 21 DAFA. The field findings suggested that two treatments of spinosad may provide a suffiecient strawberry-crop protection. Results of pretreating strawberries bioassays confirmed that pyrethroids, spinosyns, avermectin (emamectin-benzoate) and diamide (cyantraniliprole) caused excellent activities, providing adult mortality higher than 90 and 97% at 1 and 2 DAT, respectively. They also provided significant residual activities against D. suzukii life stages emerging after treatment. Incontrast, neonicotinoids, and Beauveria bassiana showed insignificantly results. The same trend of pretreating strawberries bioassay was repeated within the dipping infested-strawberries bioassay, except that acetamiprid showed good residual control against the D. suzukii individuals emerging. The third experiment investigated potential of the entomopathogenic bacterium, Photorhabdus luminescens as biological agent on D. suzukii. Efficacy of P. luminescens was assessed at different bacterial cell concentrations against third-instar larvae and pupae of D. suzukii under laboratory conditions. Larvae at 4 DAT were significantly affected by bacterial treatments when fed toxins; dipping bioassay was less effective. Following oral and dipping bioassays at concentration of 3.5×108 cells mL-1, total mortalities of 97 and 87% were recorded, respectively. For pupae, the concentration of 3.5×108 cells mL-1 caused a pupae mortality of 64 and 47%, and a total mortality of 100 and 73.33%, respectively in the direct-spray and dipping bioassays. It could be concluded that P. luminescens may play a vital role for managing D. suzukii. The last work principally focused on preparing and characterizing new controlled release formulations of lambda-cyhalothrin to improve its biological performance against D. suzukii. Chitosan (CS) loaded lambda-cyhalothrin (LC) nanoparticles were prepared using the ionotropic gelation. Tripolyphosphate (TPP) and alginate (ALG) were used as crosslinking agents with CS. The optimum encapsulation efficiency (73.6%) and loading capacity (51.4%) were obtained by a 0.4% CS high molecular weight, 0.3% ALG cross-liking agent, and LC concentration of 1% and at stirring rate of 500 rpm. The nanoparticle size of this formulation was about 416 nm (polydispersity index: 0.447) and a zeta potential of -19.8. Transmission electron microscope (TEM) imaging showed a spherical, smooth and almost homogenous structure for nanoparticles. Fourier transform infrared (FTIR) spectroscopy confirmed linking between tripolyphosphoric groups of TPP with ammonium groups of chitosan, and between ALG and CS in the nanoparticles. The release profile of LC loaded CS nanoparticles cross-linked with TPP exhibited an initial burst release of about 30-40% in the first hour followed by controlled release of 50-60% for the subsequent 5 hours. However, the release profile of LC loaded CS nanoparticles cross-linked with ALG showed a constant sustained release of the pesticide among the time of the release study. All prepared formulations significantly caused adult mortality at 2 and 16 HAT, with a best activity in the formulation of lowest nanoparticle size (278 nm). Most prepared controlled release formulations based on LC suggested activity greater than the efficacy of the commercialize insecticide, Karate-zeon® (lambda cyhalothrin 10% CS).