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Type: Thesis
Title: Interactions between Plutella xylostella, Diadegma semiclausum and some generalist predators of brassica crops.
Author: Lankin Vega, Gabriela
Issue Date: 2011
School/Discipline: School of Agriculture, Food and Wine
Abstract: While much is known about the diamondback moth, Plutella xylostella (L.) (Plutellidae) (DBM), the most important pest of brassica crops worldwide, there is little understanding about the dynamics of predatory invertebrates in brassica systems. Thus, the main objective of this work was to identify and study some interactions that occur among the parasitoid Diadegma semiclausum Hellen (Ichneumonidae), some commonly found predators and DBM, which may impact on biological control of this pest. Some novel key interactions were identified. First, predation of early DBM instars by Coccinella undecimpunctata Linnaeus, Coccinella transversalis (Fabricius) (Coccinellidae) and Micromus tasmaniae (Walker) (Hemerobiidae) was verified, even in the presence of Myzus persicae Sulzer (Aphididae). However, consumption decreased with the increasing availability of the aphid, suggesting these predators may display a low but consistent consumption of DBM, which may increase in periods of scarcity of alternative prey. Second, this study elucidated the modification in the behaviour and movement of larval DBM caused by D. semiclausum. Despite coincidental intraguild predation on the parasitoid, an increase in predation on DBM was observed when D. semiclausum and either of two hemipteran predators, Oechalia schellenbergii Guérin-Méneville (Pentatomidae) or Nabis kinbergii Reuter (Nabidae), coexisted. This probably resulted from the higher movement rate of DBM in the presence of D. semiclausum, which made it less cryptic. And third, it was observed that DBM larvae parasitised by D. semiclausum became more vulnerable to predation by C. transversalis, probably as a result of the specific hunting and attacking mode of this predator. These results indicate that among the predatory species studied the predatory bugs and parasitoids may have a synergistic interaction that enhances biological control. Only coccinellids might disrupt biological control. However, their low level of predation on DBM and preference for aphids in the field would make this unlikely. Although the short-term experiments reported in this thesis were conducted under laboratory conditions, important mechanisms resulting from the interaction between DBM larvae, alternative prey, a larval parasitoid, and generalist predators have been identified. Understanding the impact of these mechanisms under real crop conditions and in the longterm will help developing sustainable pest management strategies in Australian vegetable crops.
Advisor: Keller, Michael Anthony
Walker, Graham
Schmidt, Otto
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2011
Keywords: Plutella xylostella; Diadegma semiclausum; biological control; generalist predator; interactions; intraguild predation; escape behaviour
Provenance: Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.
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