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Applied and Environmental Microbiology, February 2009, p. 925-930, Vol. 75, No. 4
0099-2240/09/$08.00+0 doi:10.1128/AEM.01998-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

EMA, Centre LGEI, 6 Avenue de Clavières, 30100 Alès, France,1 NPP (Arysta LifeScience), 35 Avenue Léon Blum, 64000 Pau, France,2 IRD, 158 Avenue Charles de Gaulle, 30380 St. Christol-les-Alès, France,3 INRA, Unité PSH, Agroparc, 84914 Avignon Cedex 9, France4
Received 28 August 2008/ Accepted 17 December 2008
Cydia pomonella granulovirus (CpGV) has been used for 15 years as a bioinsecticide in codling moth (Cydia pomonella) control. In 2004, some insect populations with low susceptibility to the virus were detected for the first time in southeast France. RGV, a laboratory colony of codling moths resistant to the CpGV-M isolate used in the field, was established with collection of resistant insects in the field followed by an introgression of the resistant trait into a susceptible colony (Sv). The resistance level (based on the 50% lethal concentrations [LC50s]) of the RGV colony to the CpGV-M isolate, the active ingredient in all commercial virus formulations in Europe, appeared to be over 60,000-fold compared to the Sv colony. The efficiency of CpGV isolates from various other regions was tested on RGV. Among them, two isolates (I12 and NPP-R1) presented an increased pathogenicity on RGV. I12 had already been identified as effective against a resistant C. pomonella colony in Germany and was observed to partially overcome the resistance in the RGV colony. The recently identified isolate NPP-R1 showed an even higher pathogenicity on RGV than other isolates, with an LC50 of 166 occlusion bodies (OBs)/µl, compared to 1.36 x 106 OBs/µl for CpGV-M. Genetic characterization showed that NPP-R1 is a mixture of at least two genotypes, one of which is similar to CpGV-M. The 2016-r4 isolate obtained from four successive passages of NPP-R1 in RGV larvae had a sharply reduced proportion of the CpGV-M-like genotype and an increased pathogenicity against insects from the RGV colony.
Published ahead of print on 29 December 2008.
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