Adaptation to exclusion netting of the codling moth (Cydia pomonella L.) in apple orchards

Abstract: Due to widespread insecticide resistance to granuloviruses, increasing economic losses due to the codling moth (Cydia pomonella L., Tortricidae, Olethreutinae) have been recorded in organic orchards in France. Exclusion netting of the tree canopies, using a net named Alt’Carpo, is used as an alternative to insecticides in southern France. Laboratory and field behavioural tests and observations in a network of commercial orchards have shown that the moths were able to lay eggs through the nets and to escape. It was thus supposed that the efficacy of the nets results from altering the reproduction of the pest mainly by preventing it from flying over the canopy for reproductive encounters (Sauphanor, 2012). Despite the good efficacy of this method in commercial orchards, some cases of failures raised the question of the evolution of the pest towards a modified behaviour enabling reproduction under nets. We investigated this hypothesis by comparing the fecundities and fertilities in confined space of four codling moth populations two being collected in two orchards, covered either by single row or single plot nets, and two being control populations from orchards without nets. Further their fecundities and fertilities were compared to a reference lab strain.All populations were collected as diapausing larvae, and analyzed in the following spring at adult emergence. To assess fertility and fecundity in confined space, individual pairs were confined in small boxes in the laboratory. Populations differed significantly from controls in terms of fecundity in the case of single plot netting, but not in single row netting. This may be the sign of adaptation in the case of single plot netting indicating that the second method could be the most sustainable.