Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2studies on mechanisms of CPB resistance to them willallow the development of an enterprising strategy fordelaying CPB resistance. Bioassays of phenylpyrazolesand chloronicotinyls for resistance monitoring in CPBhave been performed at the Institute of Plant Protectionin Poznan since 2001(Wegorek et al. 2001)MATERIALS and METHODSLaboratory Tests Method: In laboratory tests thestandard method recommended by the InsecticideResistance Action Committee (IRAC method nr.7) wasused. A representative sample of CPB insects (larvae 2-st-instar or second generation adults) in selected fieldpopulations and on sufficient non-infested, untreatedleaves was collected for testing.CPB Populations: The 6 insect populationsoriginated from three regions of Poland (Winna Gora,Rogalinek, Skoki, and Bolewice from western Poland,Rarwino from northern Poland, and Badrzychowicefrom central Poland).Accurate dilutions of the tested compound fromcommercially available product were used indetermined doses.Chemicals:Chloronicotinylsimidacloprid (commercially-available productConfidor 200 Sl) LC50 and LC 95 werecalculated (recommended field concentration30-50 ppm)acetamiprid (commercially-available productStonkat 160 SL) LC50 and LC 95 werecalculated (recommended field concentration30-50 ppm) )thiamethoxam (commercially-availableproduct Actara 25 WG) ) LC50 and LC 95were calculated (recommended fieldconcentration 50-67 ppm)Phenylpyrazolesfipronil (commercially-available productRegent 200 S.C.) LC50 and LC 95 werecalculated (recommended field concentration50- 67 ppm)Leaves were dipped in water for untreated controland other leaves in tested insecticides liquid for aboutfive seconds and placed on paper towel to dry.Untreated and treated dry leaves were placed into 10cm diameter Petri dishes with 10 cm diameter filterpaper, and 10 larvae or adults insects were placed ineach dish. 5 or 10 replicates were conducted for eachconcentration and control.A final assessment of the lethal effects of thephenylpyrazoles and chloronicotinyls insecticide wasdetermined 72 hours after application and expressed aspercent mortality at each dose, correcting for untreated(control) mortalities using Abbott's formula (Abbot1925). Untreated mortality was quoted. The lethalconcentration at which > 50% of insects are killed -LC50 (ppm) and lethal concentration at which > 95% ofinsects are killed -LC 95 (ppm) were calculated usingthe probit analysis Finney method (Finney 1952).At each assessment, larvae or beetles were classedas either (a) unaffected, giving a normal response (suchas taking a co-ordinated step) when gently stimulatedby touch, or (b) dead or affected, the latter giving anabnormal response to stimulation or showing abnormalgrowth which should be described. Corrected Mortality= 100 x (P-C/100-C) where P = % mortality intreatment, C = % mortality in controls.Tests were performed in the laboratory withconditions of 22-24 degrees C and a photoperiod of16:8 (L;D).RESULTS and DISCUSSION Laboratory investigations gaveno indication of resistance elicited by testedpopulations of CPB to insecticides from phenylpirazoleand chloronicotinyl groups (fpronil, thiamethoxam,imidacloprid, and acetamiprid). No significantdifferences in LC50 and LC95 values and no evidence60