Susceptibility Level of Colorado Potato Beetle (Leptinotarsa decemlineata Say) to some Pyrethroids andNereistoxin Derivative (Bensultap) Insecticides in Poland in 2002INTRODUCTION Poland is a major producer of potatoes(Solanum tuberosum). This plant is cultivated on about1,000,000 ha (2002) in this country but the averagecrop is very low - 17.2 t/ha. Colorado potato beetle(CPB) (Leptinotarsa decemlineata Say) is the mostserious potato pest in Poland and considered to be thePolish pest with the highest likelihood of developinginsecticide resistance (Wegorek et al. 2001) All classesof insecticide have been widely used to control CPB inPoland. A 50 year period of intensive selectionpressure has lead to CPB resistance to five majorchemical classes of insecticide: chlorinatedhydrocarbons, organophosphates, carbamates,nereistoxin analoques, and pyrethroids (Pruszynski etal. 1988, Wegorek et al. 2001).For many years pyrethroids (deltamethrin,cypermethrin, alpha-cypermethrin, zeta-cypermethrin,lambda cyhalothrin, esfenvalerate, fenvalerate, andethofenprox) and bensultap have held the primary placein CPB control in Poland. Over a period of 26 years forpyrethroids and 17 years for bensultap, these twoclasses of insecticides have been most commonly usedfor controlling CPB in Poland (Szczesna et al. 1990,Przybysz et al. 1996, Pawinska M. 2000, MrowczynskiM. 2000). Nowadays the use of pyrethroids and thenereistoxin derivative (bensultap) is systematicallydecreasing. The cases of observed CPB resistance forboth classes under practical conditions have increased.Bioassays of determined pyrethroids andnereistoxin derivative (bensultap) for resistancemonitoring in CPB were performed in western, central,and northern regions of Poland (Institute of PlantProtection in Poznan, Plant Breeding andAcclimatization Institute in Bonin, and Institute ofOrganic Industry in Warsaw). Project P06r 126 21 issupported by the Polish <strong>State</strong> Committee For ScientificResearch.METHODS<strong>Lab</strong>oratory Tests: In laboratory tests the standardmethod recommended by Insecticide Resistance ActionCommittee (IRAC method nr.7) was used. Fourteeninsect populations were used from three regions ofPoland: 5 populations from the western region - WinnaGora, Rogalinek, Plewiska, Skoki, and Bolewice; 3populations from northern region - Czarnoszyce,Bonin, and Zamarte; and 6 populations from the centralregion - Bielawy, Rudka, Radachowek, Gorzno,Chobot, and Rabiez. A representative sample of CPBlarvae (2-st-instar) in selected field populations andsufficient non-infested, untreated leaves were collectedfor testing.Chemicals:Pyrethroids -alpha-cypermethrin (commerciallyavailableproduct Fastac 100 EC) 20, 10, 5ppm concentrations were tested(recommended concentration in Poland: 20-33 ppm)lambda-cyhalothrin (commerciallyavailableproduct Karate 025 EC ) 10, 5, 2,5ppm concentrations were tested(recommended concentration in Poland: 15-25 ppm)deltamethrin (commercially-availableproduct Decis 2,5 EC ) 20, 10, 5 ppmconcentrations were tested (recommendedconcentration in Poland: 15-25 ppm)Nereistoxin analogues -bensultap (commercially-available productBancol 50 WP ) 20, 10 ppm concentrationswere tested (recommended concentration inPoland: 500- 667 ppm)Accurate dilutions of the tested compound fromcommercially available products were used indetermined doses.Leaves were dipped in water for untreated controland other leaves in tested insecticide concentrationliquids for about five seconds and placed on papertowel to dry. Untreated and treated dry leaves wereplaced into 10 cm diameter Petri dishes with 10 cmdiameter filter paper and 10 larvae were placed in eachdish. 3-5 replicates were conducted for eachconcentration and control.A final assessment of the lethal effects of thepyrethroides insecticides were determined after 72hours and assessment of the nereistoixin analogue(bensultap) was determined after 120 hours afterapplication and expressed as percent mortality at eachdose, correcting for untreated (control) mortalitiesusing Abbott's formula (Abbot 1925). Untreatedmortalities were quoted.At each assessment, larvae were classed as either:(a) unaffected, giving a normal response (such astaking a co-ordinated step) when gently stimulated bytouch, or (b) dead or affected, the latter giving anabnormal response to stimulation. Corrected Mortality= 100 x (P-C/100-C) where P = % mortality intreatment, C = % mortality in controls.
Spring 2003 Resistant Pest Management Newsletter Vol. 12, <strong>No.2</strong>Tests were performed in the laboratory withconditions of 22-24 degrees C and a photoperiod of16:8 (L;D).RESULTS and DISCUSSIONPopulations from all three provinces demonstratedsome level of resistance to one or more pyrethroidsinsecticides (deltamethrin, alpha-cypermethrin,lambda-cyhalothrin). In laboratory studies (2002) thepyrethroids insecticides were less effective incontrolling CPB larvae. Survival at 20ppmconcentration in the case of alpha-cypermethrine anddeltamethrin and 10ppm concentration in the case oflambda-cyhalothrin indicated the occurence of strongfield resistance in tested populations.The populations from the central and northernregions of Poland were more resistant to testedpyrethroids than populations from the western region.CPB strains tested in 2002 were not tolerant tonereistoxin analogue (bensultap). The LC50 data forbensultap from 1998 (western populations) rangedfrom 11.86 to 14.59 (Wegorek et al. 1999) were notsignificantly different than data in 2002. The resultsindicated that populations tolerant for pyrethroids werenot cross-resistant to bensultap. The widespread use ofpyrethroids in Poland can lead to control failure.Understanding the conditions that favour thedevelopment, the causes, and the mechanisms ofresistance are the crucial challenges for the future ofpyrethroid use to CPB control in Poland.The constant monitoring of CPB susceptibilitylevels to insecticides used in Poland and studies onmechanisms of CPB resistance to those insectivideswill allow for the development of the best strategy fordelaying CPB resistance. At present the generalprinciples of the management strategy involve therational application of all recommended insecticides57
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