Herbivore‐induced plants do not affect oviposition but do affect fitness of subsequent herbivores on canola

Abstract

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.

Host-mediated, cross-generational intraspecific competition in a herbivore species

“…Herbivore feeding behavior is an important determinant of herbivore adaptive response to plant defenses (Karban, 2011;Weeraddana & Evenden, 2019). Yet, in our case, larvae were not allowed to move freely and leave the potted tree to find a more suitable host, or more generally escape competition.…”

“…However, several authors reported a mismatch between prior herbivory effects on female oviposition preference vs larval growth, consumption or survival of their offspring (Godinho et al, 2020; Wise & Weinberg, 2002; Bergamini & Almeida-Neto, 2015; Martinez et al, 2017). For instance, Weeraddana and Evenden (2019) found that herbivory by the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) on canola plants ( Brassica napus L.) had no effect on subsequent oviposition by the bertha armyworm, Mamestra configurata Walker (Lepidoptera: Noctuidae) whereas its larvae had reduced growth on previously damaged plants. Thus, in order to quantify the effect of prior herbivory on subsequent herbivore performance, we need to assess how it affects both female choice and progeny performance in attacked and non-attacked hosts.…”

Host-mediated, cross-generational intraspecific competition in a herbivore species

“…Previous herbivory can also affect the oviposition preference of herbivores that arrive later. Several studies have demonstrated that mated females can discriminate between host plants that have been previously attacked by insect herbivores (Wise & Weinberg, 2002;Stam et al, 2014;Moura et al, 2017;Barnes & Murphy, 2018;Moreira et al, 2018;Weeraddana & Evenden, 2019), thereby reducing competition between herbivores separated in time. Mated females can directly detect the present, past and possibly future presence of competitors themselves.…”

“…However, several authors reported a mismatch between prior herbivory effects on female oviposition preference vs larval growth, consumption or survival of their offspring (Wise & Weinberg, 2002;Bergamini & Almeida-Neto, 2015;Martinez et al, 2017;Godinho et al, 2020). For instance, Weeraddana and Evenden (2019) found that herbivory by the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) on canola plants (Brassica napus L.) had no effect on subsequent oviposition by the bertha armyworm, Mamestra configurata Walker (Lepidoptera: Noctuidae) whereas its larvae had reduced growth on previously damaged plants. Thus, in order to quantify the effect of prior herbivory on subsequent herbivore performance, we need to assess how it affects both female choice and progeny performance in attacked and non-attacked hosts.…”

Introduction: host plant choice and feeding ecology of insects

“…Even though the study found that long‐distance cues were more influential than short‐distance cues, the authors clearly identify a synergy between the two cue types. Weeraddana & Evenden () describe how feeding‐induced defenses by a specialist herbivore, diamondback moth, Plutella xylostella L. (Lepidopera: Plutellidae), in canola deterred subsequent herbivory by a generalist herbivore, bertha armyworm, Mamestra configurata Walker (Lepidoptera: Noctuidae), and negatively impacted its fitness. Mechanical damage simulating the specialist feeding, on the other hand, did not affect the generalist feeding and fitness.…”