Experimental and Applied Acarology (2012) 57, 53-64

Paola Tirello, Alberto Pozzebon, Stefano Cassanelli, Thomas Van Leeuwen and Carlo Duso (2012)
Resistance to acaricides in Italian strains of Tetranychus urticae: toxicological and enzymatic assays
Experimental and Applied Acarology 57 (1), 53-64
Abstract: Problems with Tetranychus urticae are frequently reported in protected crops in Italy, particularly in roses where many introduced acaricides show a progressive loss of effectiveness. We have conducted bioassays to assess the response of some Italian strains of T. urticae to a number of acaricides. These include compounds that were widespread and frequently used in the past, but also some recently registered compounds. We investigated two T. urticae strains collected from rose growers where control failures were reported (SAN and PSE), together with a strain collected from unsprayed vegetables (BOSA). Adult females of the rose strains (SAN and PSE) were resistant to tebufenpyrad (Resistant Ratio-RR, RR₅₀ = 48.4 and 163.6) and fenpyroximate (RR₅₀ = 74.1 and 25.9) when compared to the susceptible BOSA strain. Lethal concentrations for these products were higher than the registered field rate. The PSE strain proved to be highly resistant to abamectin (RR₅₀ = 1,294.1). Variation in bifenazate susceptibility was detected amongst strains, but LC₉₀ values of SAN and PSE were still in the range of the registered field rate. In egg bioassays, the SAN and PSE strains exhibited high resistance levels to clofentezine (RR₅₀ = 66,473 and 170,714), hexythiazox (RR₅₀ = 70,244 and 159,493) and flufenoxuron (RR₅₀ = 61.9 and 117.9). But the recently introduced ovi/larvicides etoxazole and spirodiclofen exhibited high activity on all strains. The activity of detoxifying enzymes such as esterases, glutathione-S-transferases (GSTs) and cytochrome P450 monooxygenases (MFOs) was determined in these strains as a preliminary attempt to identify potential resistance mechanisms. Enzymatic assays showed that the rose strains exhibited 2.66 and 1.95-fold increased MFOs activity compared to the susceptible strain. Assays for GSTs revealed that only the SAN strain exhibited a significantly higher activity. In contrast, only the PSE strain showed a significant higher hydrolysis of 1-naphthyl acetate.
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Link to article at publishers website
Database assignments for author(s): Alberto Pozzebon, Carlo Duso, Thomas Van Leeuwen

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Tetranychus urticae	Rosa (crop)	Italy