Effects of insecticides on the mortality and physiological stress of European Corn Borer larvae (Ostrinia nubilalis Hbn.) and the occurrence of secondary fungal infections in maize

Abstract

IZ  Kukuruzni plamenac (Ostrinia nubilalis Hbn.) predstavlja jednu od najznačajnijih štetočina kukuruza, kako u Srbiji, tako i u Evropi i Sjedinjenim Američkim Državama. Za suzbijanje kukuruznog plamenca u usevu kukuruza mogu se koristiti različite metode, ali za sada najrasprostranjenije je hemijsko suzbijanje. U tu svrhu postoje registrovani preparati, ali njihova efikasnost ne zavisi samo od aktivne supstance, već i od klimatskih faktora, ali i vremena i načina primene. U radu je ispitivana efikasnost insekticida na bazi: hlorantraniliprola, hlorantraniliprola + lambda-cihalotrina i indoksakarba, registrovanih za suzbijanje kukuruznog plamenca, kao i efikasnost različitih rokova primene hlorantraniliprola + lambda-cihalotrina. Takođe, ispitivan je uticaj larvi kukuruznog plamenca i intenziteta napada ove vrste na pojavu i intenzitet zaraze gljiva iz roda Fusarium, kao i uticaj različitih aktivnih supstanci na komponente antioksidativnog sistema zaštite gusenica kukuruznog plamenca.  Nakon četiri godine ispitivanja efikasnosti insekticida i dve godine ispitivanja uticaja rokova hemijskog tretmana u suzbijanju kukuruznog plamenca, sprovedenih mikoloških i biohemijskih istraživanja, zaključeno je da su najveću efikasnost u suzbijanju gusenica i smanjenju oštećenja prouzrokovanih larvama kukuruznog plamenca, kako u stabljici kukuruza tako i u klipu, imali tretmani hlorantraniliprolom i hlorantraniliprolom + lambda-cihalotrinom. Tretman indoksakarbom je pokazao najmanju ali i dalje zadovoljavajuću efikasnost. Hemijski tretman imao je pozitivan efekat na prinos u svim godinama ispitivanja. Tretman hlorantraniliprolom je najviše uticao na prinos u 2013. i 2016. godini (35,3 % i 21 % viši u odnosu na kontrolnu grupu). U 2014. i 2015. godini, kada je brojnost gusenica kukuruznog plamenca bila značajno niža, najveći uticaj na prinos imao je tretman hlorantraniliprolom + lambda-cihalotrinom (11,3 % i 15,1 %). Tretmani hlorantraniliprolom i hlorantraniliprolom + lambda-cihalotrinom najviše su uticali na prinos u svim ispitivanim godinama. Ogledom ispitivanja rokova hemijskog tretmana, u obe godine istraživanja, utvrđeno je da je najveći uticaj na prinos ostvaren pri tretmanu kukuruza u periodu početka leta kukuruznog plamenca (19 i 40,6%).  Ustanovljeno je da je u godini sa najvećom frekvencijom gusenica i oštećenja kukuruznog plamenca, tretman hlorantraniliprolom značajno uticao na smanjenje učestalosti oštećenih klipova i ujedno je u istom tretmanu zabeležena statistički značajno niža učestalost fuzarioznih klipova, ali pozitivna korelacija smanjenja oštećenosti klipova i fuzarioza nije potvrđena u svim oglednim godinama. Takođe je pokazano da je uticaj insekticida na smanjenje oštećenja klipa prouzrokovanih ishranom insekata i plesnivosti klipa evidentan u godinama sa visokom frekvencijom gusenica, iako se plesnivost klipa može javiti i nezavisno od oštećenja klipa u godinama sa povoljnim klimatskim uslovima za razvoj gljiva. Najzad, rezultati su pokazali da su sva tri tretmana insekticidom uticala na izmenu fizioloških pokazatelja larvi kukuruznog plamenca kao odgovor na oksidativni stres,  različit potencijal za indukciju oksidativnog stresa, kao i da reakcija larvi kukuruznog plamenca na delovanje insekticida zavisi od tipa aktivne materije.  Reakcija larvi kukuruznog plamenca na delovanje insekticida zavisi od tipa aktivne materije. Složeno delovanje korišćenih insekticida indukuje mehanizme antioksidativne odbrane i detoksifikacije u telu larvi i kod sva tri insekticida ogleda se u visokoj aktivnosti GST u odnosu na kontrolnu grupu. S druge strane, uočena je razlika u odgovoru na delovanje insekticida kod enzima SOD, CAT i GR. Ovim istraživanjem je dokazano da se druga generacija kukuruznog plamenca može uspešno suzbijati u usevu merkantilnog kukuruza sa samo jednim tretmanom, da efikasnost tretmana zavisi i od vremena primene, kao i da je najefikasnija aktivna supstanca za tu svrhu hlorantraniliprol. Potvrđen je uticaj tretmana insekticidom na smanjenje plesnivosti klipa posrednim putem kroz smanjenje broja oštećenih klipova,  ali ne u svim godinama istraživanja. Larve koje su preživele hemijski tretman pokazale su izmenjene fiziološke pokazatelje oksidativnog stresa, ali za potpunije razumevanje mehanizama enzimske detoksifikacije potrebna su dalja istraživanja.AB  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