Carabid and Staphylinid beetles from agricultural land in the lower Fraser Valley, British Columbia

Pit-traps were emptied every two or three days for two seasons in crop, fallow, and grass plots to determine the species and population density of Carabidae and Staphylinidae associated with agricultural land, and their relationship with brassica crops. Half of the plots were enclosed by plastic barriers and the beetles were trapped to extinction: half were not enclosed. Thirty-three carabid and 16 staphylinid species were captured. The dominant species was the small, generalized. European carabid predator, <i>Bembidion lampros</i>, which had a population on crop and fallow land of about 29000/hectare. It was almost absent in grass. Other numerous carabids were <i>Harpalus aeneus</i>, <i>Calathus fuscipes</i>, and <i>Clivina fossor</i>, all introduced European spp., with populations of almost 2000, 5600, and llOOO/hectare respectively. The first and third of these were scarce in grassland but the second was abundant. In plots of Brussels sprouts <i>Aleochara bilineata</i>, a staphylinid, was effectively parasitic on root maggots, and averaged more than 6000/hectare. Soil cores taken in October centred on a Brussels sprouts plant averaged 26.4 <i>Hylemya puparia</i> per core of which 44% were parasitized by <i>A. bilineata</i>