The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is oligophagous on plants in the Brassicaceae, and is considered one of the most significant insect pests of canola (Brassica napus L.), a major oilseed crop grown in the Prairie Provinces of Canada. The bertha armyworm (BAW), Mamestra configurata Walker (Lepidoptera: Noctuidae), is a generalist herbivore that preferentially feeds on canola plants. In the canola growing season in the Prairie Provinces of Canada, DBM feeding occurs prior to BAW herbivory. In this study, we test the effect of DBM herbivory on subsequent host use by BAW. Oviposition by female BAW was not influenced by previous DBM‐herbivory or mechanical damage of canola plants. Bertha armyworm larvae were deterred from feeding on canola previously damaged by DBM and larvae developed into lighter pupae when reared on DBM‐damaged plants. Bertha armyworm pupae that developed from larvae fed on mechanically damaged plants had similar pupal weights to those fed undamaged plants. Adult BAW reared on canola with previous DBM feeding damage had marginally smaller wings than moths reared on canola treated differently. The combination of these results suggests that herbivory by the brassicaceous specialist, DBM, negatively influences host use and larval performance by the generalist, BAW, on canola.

Bertha armyworm Mamestra configurata Walker (Lepidoptera: Noctuidae) is a generalist herbivore that feeds on several crops in different plant families. Canola Brassica napus L. (Capparales: Brassicaceae) is one of the most favored host plants making the bertha armyworm a significant insect pest in the Canadian Prairie Provinces. The performance of the bertha armyworm on canola may vary with the quality of the canola plant. We tested the impact of plant nutrition and canola variety on oviposition and subsequent larval development of the bertha armyworm. A range of fertilization levels (0.0, 1.0, 3.0, and 5.0 g/pot) were applied to three different canola varieties: Clearfield 5535 CL, Roundup Ready hybrid 6060RR, and Q2. The total number of eggs laid on plants in a no-choice experiment increased with fertilizer level but a similar number of eggs were laid on plants that received moderate and high fertilizer treatments. Larvae reared on plants that received the moderate fertilizer application yielded heavier pupae than those reared on plants with low and high fertilizer treatments. Most eggs were laid on the Q2 variety when compared to Clearfield 5535 CL and Roundup Ready 6060 RR. Bertha armyworm females preferred to lay eggs on plants that received moderate or high fertilization over plants with the low fertilizer treatment. Plant leaf tissue nutrient content and plant growth were highest in plants that received moderate and high fertilizer treatment. We conclude that bertha armyworm oviposition behavior and larval performance are influenced by fertilizer treatment and canola variety.

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