PROJECT RESULTS

Biological Control of Bertha Armyworm

Applicant: 

Dr. N.J. Holliday
Department of Entomology
University of Manitoba
Winnipeg, Manitoba  R3T 2N2  Canada

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusion

ARDI Project:

#98-094

Total Approved:

Date Approved:

Project Status:

Completed December, 2003

Background and Objectives:

Bertha armyworm Mamestra configurata, is one of the most important insect pests of canola in western Canada, and is currently controlled mostly by insecticides. Losses to producers in the last major outbreak were over $70 million in a two year period, of which about half was lost yield and the remainder was the cost of insecticidal control. The project assessed the potential of the natural enemies of the European relative of the bertha armyworm, M. brassicae, to be used as biocontrol agents of M. configurata.

The specific objectives of the study were:

1. To determine the seasonal progression of the natural enemy complex attacking Mamestra brassicae.

2. To determine the impact of egg parasitoids and larval parasitoids on M. brassicae.

3. To determine what parasitoids are attacking other lepidopteran species (i.e. Pieris brassicae, P. rapa and Autographa gamma) in the habitat of M. brassicae.

4. To assess patterns of parasitism of M. brassicae by the larval parasitoid Microplitis mediator in controlled conditions.

Procedure and Project Activities:

The two components of the study were field studies of the parasitoids of M. brassicae in organic cabbage fields in Switzerland in 1998 and 1999, and detailed laboratory studies of the attack responses of females of the larval parasitoid, Microplitis mediator.

Results and Discussion:

The principal findings of the study were:

• In cabbage fields in Switzerland, M. brassicae has two generations, in contrast to the single generation of M. configurata in canola in prairie Canada.

• Six parasitoids were detected in M. brassicae, of which three were relatively abundant.  These were the egg parasitoids Trichogramma buesi and Telenomus sp., and the larval parasitoid Microplitis mediator.

• Both egg parasitoids attacked the second generation of M. brassicae in both study years, and the first generation in one year; but they did not occur in all cabbage fields. Each of these parasitoids parasitized all the eggs in the egg masses they attacked; no egg masses had both parasitoids.

• The larval parasitoid Microplitis mediator was present in all fields in both generations of the host. The percentage parasitism was inversely related to the number of host larvae on the cabbage plant. Killing power of this parasitoid appears to be limited by the egg load of the female.

• Female M. mediator attack first, second and third instar host larvae without discriminating among them even though parasitoid success is poor in third instars. Poor discrimination between more and less suitable host stages may impair establishment of this parasitoid, but assist in survival during periods of low host density.

• The only other host attacked by M. mediator in cabbage fields was Autographa gamma, like Mamestra, a member of the Noctuidae.

Conclusion:

It is recommended that future M. mediator introductions be from regions where the original host has one generation and has a similar timing of vulnerable stages to those of M. configurata in prairie Canada.

Acknowledgements:

This project was made possible by funding from the Governments of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI), by funding from the Government of Canada through Agriculture and Agri-Food Canada and by funding from the Canola Council of Canada.

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