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NORONHA ET AL. : LEPTINOTARSA DECEMLINEATA SUSCEPTIBILITY TO INSECTICIDES Differential susceptibility to insecticides by
Leptinotarsa decemlineata
[Coleoptera: Chrysomelidae] populations from
western Canada
Christine Noronha1,2, Grant M. Duke1, Jason M. Chinn1,and Mark S. Goettel1,3 PHYTOPROTECTION 82 : 113-121
The susceptibility of Colorado potato beetles (Leptinotarsa decemlineata)(CPB) from three provinces in western Canada was measured using a filterpaper bioassay to substantiate the reported insecticide resistance by thebeetle in Manitoba, and to compare the situation there to beetle popula-tions from Saskatchewan and Alberta. Susceptibility of beetles was mea-sured against five insecticides: the organophosphates, azinphos-methyl(Guthion), and methamidophos (Monitor); the pyrethroid, permethrin (Am-bush); the organochlorine, endosulfan (Endosulfan); and the carbamate,carbaryl (Sevin). All 12 populations tested from Manitoba were found tohave resistance to one or more of the insecticides. All populations wereclassified as either having resistance or intermediate resistance to per-methrin; two of the populations were classified as having resistance toazinphos-methyl and three to methamidophos. Two of four populationsfrom Saskatchewan were classified as having intermediate resistance toazinphos-methyl and methamidophos. Intermediate resistance to per-methrin was recorded in 12 of the 13 populations from Alberta, with onlyone being highly susceptible. Two populations showed evidence of inter-mediate resistance to azinphos-methyl and three to methamidophos. In allthree provinces, survival rate from different egg masses within the suscep-tible populations ranged from 0-100%, indicating the presence of individ-uals with either resistance, intermediate or high susceptibility within thesepopulations. With the expanding potato acreage in western Canada andthe detection of the CPB populations with resistance to insecticides, aresistance management program must be implemented to prevent therapid selection of resistant populations.
[Sensibilités variées aux insecticides de populations de Leptinotarsa
decemlineata [Coleoptera : Chrysomelidae] de l’Ouest canadien]
La sensibilité du doryphore de la pomme de terre (Leptinotarsa decemlin-eata) de trois provinces de l’Ouest canadien a été mesurée par bioessai sur 1. Lethbridge Research Centre, Agriculture and Agri-Food Canada, P.O. Box 3000, Lethbridge, 2. Present address: Crops and Livestock Research Centre, Agriculture & Agri-Food Canada, 440 University Ave., Charlottetown, Prince Edward Island, Canada C1A 4N6 3. To whom correspondence should be addressed; e-mail: goettel@em.agr.ca papier filtre pour corroborer les comptes rendus faisant état de doryphoresrésistants aux insecticides au Manitoba, et pour comparer la situation auManitoba à celles de la Saskatchewan et de l’Alberta. La sensibilité desdoryphores a été mesurée pour cinq insecticides : les organophosphatesazinphos-méthyl (Guthion) et méthamidophos (Monitor), le pyréthroïdeperméthrine (Ambush), l’organochloré endosulfan (Endosulfan) et le car-bamate carbaryl (Sevin). Les 12 populations du Manitoba examinéesdémontraient de la résistance à au moins un des insecticides. Toutes lespopulations ont été classées comme étant résistantes ou moyennementrésistantes à la perméthrine; deux des populations ont été classées commerésistantes à l’azinphos-méthyl et trois au méthamidophos. Deux desquatre populations de la Saskatchewan ont été classées comme étantmoyennement résistantes à l’azinphos-méthyl et au méthamidophos. Unerésistance intermédiaire à la perméthrine a été trouvée dans 12 des 13populations de l’Alberta, alors qu’une seule était très sensible. Deuxpopulations se sont montrées moyennement résistantes à l’azinphos-méthylet trois au méthamidophos. Dans les trois provinces, le taux de survie dediverses masses d’oeufs provenant de populations sensibles variait de 0à 100 %, ce qui montre que des individus résistants, moyennement résis-tants et très sensibles coexistent dans ces populations. Avec l’expansionde la culture de la pomme de terre dans l’Ouest canadien et la détectiond’une résistance aux insecticides dans les populations du doryphore de lapomme de terre, un programme de gestion de la résistance doit être misen place pour éviter la sélection rapide de populations résistantes.
INTRODUCTION
ment (Forgash 1981; Grafius 1997;Martel 1987).
1990; Martel 1987; Roush et al. 1990).
insecticides (Harris and Turnbull 1986).
increase in insecticide resistant popula- al. 1992; Harris and Turnbull 1986).
Thus, the selection of insecticide resis- tant populations is a major threat to the resistance to insecticides in all classes, PHYTOPROTECTION 82 (3) 2001
NORONHA ET AL. : LEPTINOTARSA DECEMLINEATA SUSCEPTIBILITY TO INSECTICIDES MATERIALS AND METHODS
1997). In Alberta, the last report of the sufficient numbers of egg masses di-rectly from the field. Consequently, more potato processors establish there.
increase in the use of insecticide treat- collected from adults that arose directly er, for four populations (Portage la Prai- insecticide resistant beetle populations.
re, Selkirk 2, Winkler and Lake Diefen-baker), we had to add a few beetles sistance to the beetle in Manitoba, tocompare the situation there to beetle ter paper (5.5 cm diam., Fisher P-5) that secticide dissolved in acetone using thediagnostic concentrations calculated by Table 1. Collection localities for Leptinotarsa decemlineata from western Canada
Table 2. Insecticides tested for resistance in Colorado potato beetle populations from
western Canada using a filter paper bioassay
Susceptible and resistant laboratory strains were obtained from S. Hilton, Southern CropProtection and Food Research Centre, Agriculture and Agri-Food Canada, London, Ontario(Hilton et al. 1998). Ten egg masses of each strain were tested against each insecticide.
incubated at 23°C and 16L:8D photope-riod. When at least 50% of the eggs to its upright position after having been the exception that it had lost its resis- French (1994); egg masses showing< 50% mortality were classified as re- sistant. The proportion of egg masseswithin each population showing resis-tance (i.e. < 50% mortality) to the diag- nostic concentrations of French et al.
as follows: resistant ( > 80% of the egg PHYTOPROTECTION 82 (3) 2001
NORONHA ET AL. : LEPTINOTARSA DECEMLINEATA SUSCEPTIBILITY TO INSECTICIDES Table 3. Mean percent mortality and range per egg mass of Leptinotarsa decemlineata for
each insecticide and population tested. Numbers in bold representant resistant populations
Mean percent mortality (range) per insecticide Saskatchewan
Manitoba
30 (0-69)
26 (0-52)
17 (0-93)
14 (0-67)
28 (0-94)
<1 (0-3)
35 (0-100)
19 (0-100)
17 (0-100)
29 (0-100)
28 (0-71)
30 (0- 67)
39 (6-82)
36 (0-93)
13 (0-71)
12 (0-67)
ulations were classified as having resis- level of susceptibility to endosulfan.
intermediate levels of susceptibility. One population (population 1) of the 12 test-ed was classified as highly susceptible Figure 1. Proportion of egg masses (%) of Leptinotarsa decemlineata from the Canadian
prairie provinces with less than 50% mortality after exposure to insecticides. Susceptibility
categories are defined as follows: Resistant when > 80% of the egg masses had < 50% mortality;
Intermediate when between 20 and 79% of the egg masses had < 50% mortality; and
Susceptible when between 0 and 19% of the egg masses had < 50% mortality (see Kennedy and
PHYTOPROTECTION 82 (3) 2001
French 1994). Insecticide concentrations used were those previously determined as diagnosticfor resistant and susceptible populations from North Carolina (French et al. 1992).
NORONHA ET AL. : LEPTINOTARSA DECEMLINEATA SUSCEPTIBILITY TO INSECTICIDES were highly susceptible to at least three also be used as a base to measure thefuture development of resistance to in- over the 24-hr assay period. The appli-cation of the French et al. (1992) diag- ed low levels of resistance to pyrethroids 1982, greater than 23-fold resistance was Turnbull 1986). In a laboratory bioas-say, CPB selected sequentially for fen-valerate exhibited a 1700 fold increase DISCUSSION
in resistance to this insecticide withineight generations (Huang et al. 1994,1995). The prevalence of populations consistent with the results of a previoussurvey, where populations from 21 of to be resistant to at least one of the nine insecticides tested (Gavloski 1997).
results according to level of susceptibil- resistant beetles has already started and ity to French et al.’s (1992) diagnostic susceptibility of beetle populations from not available for us to verify these diag- population and that the development ofresistance can be very localized. A sim-ilar variation was observed in the pop- REFERENCES
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