Entomopathogenic nematodes for biological control of Psylliodes chrysocephala (Coleoptera: Chrysomelidae) in oilseed rape.

Winter oilseed rape (Brassica napus) is one of the largest crops in Europe and the cabbage stem flea beetle Psylliodes chrysocephala is one of its major pests. Since the ban of neonicotinoids for seed treatment, farmers apply pyrethroids in autumn to control the cabbage stem flea beetle. Current studies show that the insect develops resistance to this group of chemicals. Biological control with entomopathogenic nematodes (EPNs) represents a possible, environmentally friendly alternative control measure. In the present work, we considered three strategies to control the cabbage stem flea beetle: applying the nematodes against the first larval stage in the soil, against the second and third larval stages inside the plant or against the adult beetles. In laboratory experiments, we found the third larval instar to be the most susceptible stage and the adult beetle the less susceptible one. Steinernema feltiae and the cold active SDT1-IL1 Heterorhabditis bacteriophora strain, with a reduction potential of 89 and 76 %, respectively, proved to be the most virulent EPNs against P. chrysocephala in pot experiments at 15 °C. Moreover, we performed four field trials to test the efficacy of H. bacteriophora and S. feltiae against the larvae. The highest reduction in the field trials was 45% and 39%, obtained with SDT1-IL1 and a mixture of H. bacteriophora and S.feltiae, respectively. The present study provides preliminary information about the potential of EPNs to control P. chrysocephala and represents a start point for the development of a competitive and sustainable alternative to pyrethroids.