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Bacterial Insecticides and toxins for control of root flies - PS2152

Both carrot and cabbage root flies cause major economic losses to root vegetables and brassica in the UK and worldwide through the feeding of the larval stages on the plant roots. While control of these insects with chemical pesticides is possible, there is a need to find safe and effective alternative methods. Biological control involves the use of specific predators or pathogens to kill the pest insect. The major biological pesticide worldwide is the bacterium Bacillus thuringiensis (Bt), strains of which can show very potent and specific activities, each strain targeting the larvae of a narrow range of insect species. This makes Bt strains extremely environmentally safe and their use is compatible with organic production.

Despite this fact, no extensive surveys of Bt strains for activity against carrot and cabbage root fly appear to have been conducted. In this project we will screen an extensive collection of strains of Bt and other insect pathogenic bacteria for activity against root flies in an attempt to identify strains that may be of value in control programmes in the field. In addition, we will screen a collection of proteins from Bt and other bacteria, known to be active against other insects, for activity against root flies. In this way we intend to produce a resource of agents that can be used in pest control either in biological control methods or, via emerging technologies, in the production of insect resistant plant varieties.
Proposal: It is proposed that a programme of bio-prospecting for active agents against cabbage and carrot root
flies should be undertaken.
Insect Rearing: The first objective will be to establish at Cardiff, insect cultures of D. radicum and C. rosae
ensuring the rearing of sufficient numbers of larvae for bioassay.
Bioassay: As a part of this workplan, viable bioassay methods for root fly toxicity will also be established as a
deliverable that can be exploited by Defra and others working in this field.
Bacterial Testing: Collections of a large number of Bt strains are available in the Berry laboratory for testing in
assays against the insect larvae. The collection has many of the common and freely-available Bt strains
(including those known to have activity against dipteran insects). The laboratory has also produced its own
collection of strains for testing. Bt is not the only potential bacterial agent that might be used in control. The
laboratory collection also contains strains of Lysinibacillus sphaericus, Paenibacillus alvei, Brevibacillus
laterosporus and Bacillus circulans, all of which have reported activity against dipteran insects. The production
of bacterial preparations for bioassay will be an objective of this project.
At least 100 strains of Bt and at least 20 other insect pathogenic bacteria, selected from at least four
bacterial species, will be screened in this project. IP issues do not arise in the exploitation of these strains.
Bacterial strain screening will consume much of the project time-period but, as bioassays are relatively timeconsuming,
for the establishment of milestones, they will be subdivided into phases to allow progress to be
Profiling: Toxic strains can be considered for development as bio-insecticides and individual toxins may be
candidates for the subsequent production of insect resistant plants. Active strains will be profiled to characterise
their arsenal of toxins and to identify the specific components active against root flies. These individual
components will also be produced and tested for activity against the target larvae. Since the purpose of the
application is to test for active strains, it is not possible to say when, or if, such strains will be discovered. It is,
therefore, not possible to place a time-limited absolute milestone for the detailed characterisation of active
strains. Instead, these characterisations will be placed alongside milestone objectives. The individual toxins
identified in active strains will also be included in single toxin assays during the course of the project.
Toxin Testing: In addition to the testing of bacterial strains, the Berry laboratory has also created a bank of
individual crystal and vegetative toxins that can be tested specifically against the insects. Most of these toxins
have been identified for their activity against other species but there are no reports of tests against the current
root fly targets. Increasing evidence is suggesting that proteins initially characterised as toxins of one group of
insects can sometimes target other more distantly related groups (Méndez-López et al. 2003). Hence, their
testing against new targets is highly advisable. It is noteworthy that insect pathogenic nematodes can also be
used to control root flies. Mortality is caused by release of symbiotic bacteria that intoxicate the insects (Joyce
and Clarke 2008). Toxins from these symbionts, such as the toxin complex proteins, the Mcf protein and the
PirA and PirB toxins are, therefore, particularly strong candidates for use against these insects and will be tested
to determine the active agent(s) in causing root fly mortality. Such toxins will be clear candidates for the
development of novel control methods. The Berry laboratory currently has individual clones of a number of
toxins (Cyt1Aa, Cry1Ab, Cry1Ac, Cry1Ia, Cry2Aa, Cry2Ab, Cry1A, Cry4A, Cry4B, Cry6, Cry10, Cry11A, PirA/B,
Mtx1, Mtx2, BinA/B, Cry48/49, sphaericolysin) and is currently producing others. Testing of these single toxins
will take several months to complete and will be subdivided into a series of individual milestones.
Project Documents
• EVID4 - Final project report : PS2152 Final report   (267k)
Time-Scale and Cost
From: 2013

To: 2014

Cost: £101,000
Contractor / Funded Organisations
Cardiff University
Insecticide use              
Fields of Study
Pesticide Safety