Uticaj insekticida na mortalitet i fiziološki stres gusenica kukuruznog plamenca (Ostrinia nubilalis Hbn.) i pojavu sekundarnih gljivičnih infekcija na kukuruzu / Effects of insecticides on the mortality and physiological stress of European Corn Borer lar

The European Corn Borer (Ostrinia nubilalis Hbn.) is one of the most destructive pests of corn in Serbia and in other parts of its areal. In order to control its populations in maize crops a number of methods can be used, however, chemical control is the most commonly used. Several insecticides are registered for this purpose, yet their efficacy depends on a variety of factors, e.g. climatic conditions, time and mode of application. In this work the efficacy of several Insecticides (chlorantraniliprole, chlorantraniliprole + lambda-cyhalothrin and Indoxacarb) registered against the ECB was evaluated in a four year trial. In a second trial the timing of application of chlorantraniliprole + lambda-cyhalothrin was evaluated during a two year period. The possible effects of ECB larvae on the occurence and intensity of Fusarium Ear Rot in maize was also subject to evaluation in this paper. Finally, the effects of the aforementioned insecticides on the antioxidative defence system of ECB larvae was also part of this work. The results showed that the highest efficacy in reducing the number of ECB larvae and the damage they cause in maize stalks and ears were achieved in the chlorantraniliprole and chlorantraniliprole + lambda-cyhalothrin treatments, while the least efficacy values were obtained in the Indoxacarb treatment, which could still be defined as satisfactory. The chemical tretments showed positive effects on yield in all the trial years. Treatments with chlorantraniliprole had the most significant positive effects on the yields in years 2013. and 2016. with a 35.3% and 21% yield increase compared to the control. In years with the lowest pest pressure, 2014 and 2015, the highest positive impact on yield was achieved with the chlorantraniliprole + lambda-cyhalothrin treatments (11.3% and 15.1%). Treatments using chlorantraniliprole and chlorantraniliprole + lambda-cyhalothrin had the highest positive impact on yield in all trial years.Regarding the timing of application, the highest positive impact on yields were achieved when trials were undertaken at the beginning of the flight periodof the second ECB generation (19 and 40.6%). Treatments with chlorantraniliprole in trial years with the highest pest pressure considerably reduced the number of larvae and their damage to maize ears, and at the same time considerably reduced the incidence of Fusarium Ear Rot. However, this positive correlation was not confirmed in all trial years. It has been shown that the effects of insecticide treatments on the reduction of ear damage caused by insect feeding and Fusarium Ear Rot is evident in years with an increasedlarval frequency, even though FER can occur independently from ear damage in years with favourable climatic conditions for the development of the fungus. All three insecticide treatments affected the physiological parameters of ECB larvae, inducing a responce to oxidative stress. The different insecticides had a different potential for oxidative stress induction, which depends on the application of the active substance. All three insecticide treatments induced a higher activity of glutathione S-transferase compared to the control group, while different reaction towards superoxide dismutase, catalase and glutathione reductase were observed depending on the applied treatment. The results of the trials in this work showed that the second ECB generation can be managed with only one insecticide application, and that the efficacy of the treatment depends on the timing of the application. The highest results were obtained using chlorantraniliprole. The positive effects of insectide treatments on decreasing Fusarium Ear Rot incidence through the decrease of ear damage caused by ECB larvae was confirmed, however, this was not the case in all trial years. ECB larvae which survived the insecticide treatment showed clearly altered parameters of oxidative stress, however, a better understanding of the mechanisms of enzymatic detoxification should be looked for in further trials.