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 [LC 50 s]) 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 LC 50 of 166 occlusion bodies (OBs)/l, compared to 1.36 ؋ 10 6 OBs/l 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.

The codling moth (Cydia pomonella L.) is a serious pest of pome fruit. Diapausing cocooned larvae overwinter in cryptic habitats in the soil or in the bark of infested trees. The entomopathogenic nematode Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) is used to control diapausing codling moth larvae. The objective of this study was to define environmental conditions favouring the performance of the nematodes. Cocooned larvae were more susceptible than non-cocooned larvae. Susceptibility of pupae was low. To determine the influence of decreasing water activity (a w -value) on the activity of the nematodes, mortality of codling moth larvae and Galleria mellonella L. were tested in sand-sodiumpolyacrylate mixtures of variable water activity. S. feltiae was able to infect both insects at a w -values [0.9. Cocooned larvae of both insects died at lower a w -values than non-cocooned larvae. Mortality of cocooned larvae did not further increase after half an hour of exposure to nematodes, whereas the mortality of non-cocooned larvae increased with increasing exposure time. LC 50 and LC 90 considerably decrease with increasing RH. The negative influence of the relative humidity (macro environment) was less important than the effect of the water activity in the bark substrate (micro environment). The micro environment can be manipulated by applying S. feltiae with higher volumes of water. A surfactant-polymerformulation significantly increased nematode efficacy and can buffer detrimental environmental effects.

Transmission of granulovirus resistance in the RGV-8 strain of C. pomonella cannot be fully explained by the effect of a locus located on the Z chromosome. The action of other factors needs to be considered.

RFLP analysis has been used to characterise XM(v), a chromosome of Aegilops ventricosa present in a disomic addition line of wheat. This chromosome is known to carry a major gene conferring resistance to leaf rust (Lr). The analysis demonstrated that XM(v) is translocated with respect to the standard wheat genome, and consists of a segment of the short arm of homoeologous group 2 attached to a group 6 chromosome lacking a distal part of the short arm. Lr was located to the region of XM(v) with homoeology to 2S by analysis of a leaf rust-susceptible deletion line that was found to lack the entire 2S segment. Confirmation and refinement of the location of Lr was obtained by analysis of a spontaneous resistant translocation in which a small part of XM(v) had been transferred to wheat chromosome 2A.

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