Root maggot and beneficial insect dynamics in response to weed populations in canola

Habitat management through increasing plant biodiversity is known to impact insect populations, both herbivores and their natural enemies. Field studies were conducted during 2003 to 2005 at Lacombe and Beaverlodge, AB, Canada to manipulate weed populations in both species of canola, Brassica rapa L. and Brassica napus L., to investigate responses among root maggots (Delia spp.) (Diptera: Anthomyiidae) and selected species of natural enemies.;Herbicide rate manipulations enabled establishment of canola with varying densities of weeds. Root maggot damage decreased significantly with increases in monocotyledonous weed dry weights for both canola species at both study sites. The relationship between dicotyledonous weed biomass and root maggot infestations varied among sites, depending on the species of weeds that dominated at each site. As weed biomass declined the activity density of A. bilineata increased. Significant preferences for canola species were found among several important predaceous carabid beetle species and the staphylinid A. bilineata.;A diverse fauna of coleopteran predators and parasitoids exists in canola, and my research demonstrated that several species of Carabidae that prey upon root maggot eggs and larvae seem to exhibit species-specific preferences for canola species and level of weedy background. However, the usefulness of utilizing reduced herbicide rates to manipulate weed populations in canola requires some caution in light of the potential development of herbicide-resistant weeds.;Delia radicum (L.) is univoltine in canola and peak emergence occurred after approximately 346 degree-days, and 50% flight activity required approximately 325 degree-days (soil base 4.0°C). Delia platura (Meigen) is bivoltine in canola and peak emergence of the first and second generations required approximately 340 and 595 degree-days, respectively (soil base 3.9°C). Peak flight activity occurred after approximately 255 and 640 degree-days for the first and second generations, respectively. Peak levels of activity density for the root maggot predator-parasitoid Aleochara bilineata Gyllenhal, a staphylinid beetle, required 534, 380, and 559 degree-days and 195, 180, and 186 Julian days, respectively, in each of the three years. Aleochara bilineata populations in canola were well synchronized to exploit the pre-imaginal life stages of its principal hosts, D. radicum and D. platura.