Dosdall: Improving Integrated Crop Management by Conserving Natural Enemies of Insect Pests

Date: March 2007
Term: 3 years
Status: Completed
Researcher(s): Dr. Lloyd Dosdall, Department of Agricultural, Food and Nutritional Science, University of Alberta and Doug Moisey, Canola Council of Canada
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACPC, MCGA

Project Summary

Field studies were undertaken in southern Alberta and Saskatchewan during the 2006 field season to investigate different management strategies for enhancing the effectiveness of natural enemies of cabbage seedpod weevil and diamondback moth in canola. The study showed that the level of parasitism of the cabbage seedpod weevil has increased dramatically in recent years, and the hymenopteran wasp, Diadegma insulare, is capable of causing significant reductions in diamondback moth populations. Canola growers in regions infested with damaging infestations of cabbage seedpod weevil should maintain recommended seeding rates 2.5 to 4.5 lb/acre (3 to 5 kg/ha) for optimal yields and consistent times to crop maturity. However, early seeding (late April) predisposes the crop to greater attack by the cabbage seedpod weevil and should be avoided.

Canola insect pests are subject to attack by a wide range of natural enemies, comprising parasitoids, predators, and pathogens, many of which help limit or reduce pest populations. However, in spite of their economic importance, comparatively little is known of their biology and the factors that can enhance their effectiveness. The cabbage seedpod weevil, Ceutorhynchus obstrictus and the diamondback moth, Plutella xylostella are two important insect pests of canola in western Canada that can be subject to considerable population mortality by natural enemies.

Diamondback Moth Adult Source: L. Dosdall

In this project, field studies were conducted in southern Alberta and Saskatchewan during the 2006 field season to investigate aspects of improved integrated crop management by conserving natural enemies of the cabbage seedpod weevil and the diamondback moth. The overall goal of this research was to investigate different management strategies for enhancing the effectiveness of natural enemies of cabbage seedpod weevil and diamondback moth in canola. Enabling growers to rely more on control by natural enemies and less on applications of chemical pesticides should increase profitability.

The specific objectives of the project were to determine the key parasitoids responsible for causing greatest damage to the canola pests, cabbage seedpod weevil and diamondback moth and to determine aspects of the life histories of these natural enemies. Researchers wanted to determine the timing of pest movements into the crop, and subsequent invasions of their natural enemies, through the use of geographical information systems (GIS) technology. They also wanted to determine the effects of canopy manipulation of canola on cabbage seedpod weevil through altered seeding dates and seeding rates.

This study resulted in several research discoveries that are relevant to canola producers in western Canada. The study showed that the level of parasitism of the cabbage seedpod weevil has increased dramatically in recent years, due to attack by native species like Trichomalus lucidus, Necremnus tidius, Chlorocytus sp., and Pteromalus sp. Therefore, possible introductions of parasitoids from Europe should only be made if it is evident that native populations are not capable of causing acceptable levels of weevil population reduction.

Diamondback moth infestations are often assessed in the field by trapping adults or counting the number of larvae on a plant or in a given area. Researchers found substantial differences in diamondback moth numbers over relatively short distances within a crop, and discovered that diamondback moth larvae are clustered in their distributions within canola fields, rather than randomly dispersed. Therefore, monitoring/sampling of field populations of these pests should incorporate several samples so that more accurate density estimates can be obtained.

The study also found that the principal parasitoid of diamondback moth larvae in western Canada is the hymenopteran wasp, D. insulare, which is capable of causing significant reductions in populations of its host. Therefore, in years of diamondback moth outbreaks, D. insulare populations should be monitored carefully and insecticidal spraying should be avoided where densities of the wasp are high.

The study also found that cabbage seedpod weevil infestations in canola were significantly affected by date of seeding and seeding rate. Researchers concluded that canola growers in regions infested with damaging infestations of cabbage seedpod weevil should maintain recommended seeding rates 2.5 to 4.5 lb/acre (3 to 5 kg per ha) for optimal yields and consistent times to crop maturity. However, early seeding (late April) predisposes the crop to greater attack by the cabbage seedpod weevil and should be avoided.

Scientific Publications

Dosdall, L.M., B. J. Ulmer, G. A. P. Gibson, and H. A. Cárcamo. 2006. The spatio- temporal distribution dynamics of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Coleoptera: Curculionidae), and its larval parasitoids in canola in western Canada. Biocontrol Science and Technology 16: 987-1006.

Dosdall, L.M., G.A.P. Gibson, O. Olfert, B.A. Keddie, and B.J. Ulmer. 2007. Contributions to the life history, host range, and distribution of Necremnus tidius (Walker) (Hymenoptera: Eulophidae). Annals of the Entomological Society of America 100: 861-868.

Sarfraz, M., L.M. Dosdall, and B.A. Keddie. 2008. Host plant genotype of the herbivore Plutella xylostella (Lepidoptera: Plutellidae) affects the performance of its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae). Biological Control 44: 42-51.

Dosdall, L.M., G.A.P. Gibson, O.O. Olfert, and P.G. Mason. 2009. Responses of Chalcidoidea (Hymenoptera) parasitoids to invasion of the cabbage seedpod weevil (Coleoptera: Curculionidae) in western Canada. Biological Invasions 11: 109-125.

Sarfraz, R.M., L.M. Dosdall, A.J. Blake, and B.A. Keddie. 2010. Leaf nutrient levels and the spatio-temporal distributions of Plutella xylostella and its larval parasitoids Diadegma insulare and Microplitus plutellae in canola. BioControl 55: 229-244.

Full Report PDF: Improving Integrated Crop Management by Conserving Natural Enemies of Insect Pests