Keywords :

Population dynamics and natural control of pests and diseases in an orchard landscape

A very high number of orchard-wide pesticide treatments are required to control pests and diseases in apple and pear orchards. In southeastern France, the codling moth (Cydia pomonella) is the main focus of these treatments. However, the biological characteristics of this pest species (dispersal capacity, high preference for pome fruit) suggest that its abundance also depends on the spatial distribution of orchards in agricultural landscapes (quality, abundance and habitat connectivity). To test this hypothesis, codling moth abundance patterns in 80 commercial orchards located in a 50 km^² area were compared to land-use maps. It was thus shown that this pest is less abundant in pome fruit orchards surrounded by similar orchards, likely because these spatial configurations keep codling moths from avoiding pesticide treatments. Movements of females between two egg-laying events were also reconstructed via genetic analysis.

These movements were found to be mostly within orchards, but a few dispersal movements between remote orchards were documented, thus confirming the relevance of managing this pest on a supraplot scale. Finally, the natural enemies of codling moths, especially female parasitic wasps that lay their eggs in codling moth eggs or caterpillars, were studied. Molecular markers were developed to quantify parasitism and gain insight into parasitic wasp population dynamics in different landscape settings. These markers allow early detection of the three most active wasp species that attack codling moths in orchards (Ascogaster quadridentata, Pristomerus vulnerator and Perilampus tristis). Studies are also under way on the predatory habits of codling moths and the rosy apple aphid (Dysaphis plantaginae), another apple pest, in order to gain insight into trophic interactions between prey.