Novel approaches for the management of cabbage root fly
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Date
29/06/2015Item status
Restricted AccessEmbargo end date
31/12/2100Author
Deasy, William Patrick
Metadata
Abstract
Delia radicum L. (Diptera: Anthomyiidae), the cabbage root fly, is a specialist root-feeding
insect pest of Brassica crops. The impending withdrawal of chlorpyrifos, one
of the main pesticides used against D. radicum, opens new opportunities to research
alternative pest management strategies. Manipulating host plant location cues to
influence D. radicum adult and larval behaviour, along with induced plant defence
responses, offer potential integrative crop protection solutions (Chapter 1). This
thesis aimed to identify the semiochemistry underpinning D. radicum larval host
plant location, and to investigate whether plant defence induction treatments (methyl
jasmonate [MeJA], D-Fructose) and a herbivore induced volatile (dimethyl disulfide
[DMDS]) affect D. radicum larval performance and adult oviposition preference.
In choice-test bioassays, larvae were inconsistent in their responses to root exudates
collected from Brassica host plants (Chapter 2). A combined bioassay and
EthoVision® video-tracking approach was developed to record and analyse larval
movements in response to volatiles emitted from host and non-host plant roots
(Chapter 3). Larvae were significantly attracted to host plant root volatiles. Olfactory
stimuli from roots of the non-host plant onion (Allium cepa L. ‘Ailsa Craig’), which
share overlapping, yet distinctive volatile profiles to that of Brassica plants, also
elicited positive taxis. By analysing the volatile metabolome of broccoli (B. oleracea
L. convar. botrytis L. Alef. var. cymosa Duchesne ‘Parthenon’) and onion roots using
solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GCMS),
a suite of candidate volatile orientation cues were identified. A SPME-based
method was developed to non-invasively collect root volatiles in situ from
glasshouse- and field-grown broccoli plants pre- and post-D. radicum infestation
(Chapters 4, 5 and 6). GC-MS analyses revealed that sulfur compounds, showing
characteristic temporal emission patterns, were the principal volatiles released by
roots in response to damage. This new method, which has potential for wide
application in chemical ecology research, allows the study of volatiles in the soil in
situ that are critical for interactions between trophic levels. In EthoVision®
bioassays, a major volatile constituent of broccoli roots, DMDS, was attractive to
larvae, but toxic at the highest dose tested (Chapter 3).
Glasshouse and on-farm experiments using broccoli were conducted to evaluate the
efficacy of MeJA, D-Fructose and DMDS against D. radicum compared to
commercially available crop protection products (chlorpyrifos [Dursban® WG],
spinosad [Tracer®], Steinernema feltiae Filipjev [Nematoda: Steinernematidae]
[Entonem] and garlic granules [ECOguard®]). MeJA and garlic reduced larval
performance under glasshouse conditions whereas D-Fructose and DMDS did not at
the concentrations tested (Chapter 7). In field studies, MeJA combined with reduced
rate chlorpyrifos, spinosad, and S. feltiae all showed partial efficacy for controlling
D. radicum larvae. Inherent field site, weather and D. radicum population density
variability highlighted that glasshouse results cannot always be reproduced in more
complex field environments (Chapter 8). Further research is needed into formulation,
mode of application and timing to improve efficacy of promising treatments that may
help in future integrated pest management (IPM) for this key pest in the absence of
existing pesticides.