SpK
SpK is a bio-insecticide based on the bacterium Yersinia entomophaga. The whole organism, toxic metabolites and identified genes all display insecticidal properties when injested by susceptible insect pests. The level of this insecticidal activity compares favourably with commercial bio-rational products.
SpK:
- Is at least as efficacious as Bt, but against a broader spectrum of insect pests,
- Will be commercially competitive with Bt
- May be more persistent on insect food surfaces after application
- Being yet undeveloped, has substantial potential for future optimisation in a development process
- At least as the whole organism, qualifies as a suitable component of ‘organic’ insect control regimes.
- Has no detected mammalian or environmental toxicity concerns that might prejudice product registrations
- Is not difficult, complicated or expensive to produce by fermentation and may be formulated into dry preparations for packaging, storage and distribution under reasonable ambient conditions. These dry formulations are conveniently dispersed in water for spray or similar application onto surfaces of pest insect food.
In addition:
SpK is currently being tested for insecticidal activity on diamond back moth larvae that are resistant to Bt, spinosad or a pyrethroid insecticide. It is expected that SpK will display no cross-resistance to any of these insecticide groups. Therefore SpK can be expected to a valuable tool in resistance prevention or management programmes that involve these insecticides. SPK may complement, replace or compete with other insecticides depending on biological and commercial considerations.
After 7 days growth from seed 16 cabbage seedlings were assigned to each of 4 treatments:
1. Control, no treatment
2. EN-65 in 0.03% (v/v) DuWett (108 cfu/mL-1)
3. Dipel® DF (NuFarm; Bt var. kurstaki) in 0.03% (v/v) DuWett at recommended ‘low’ field use rate for DBM (equiv. to 0.5g/L-1)
4. Yates Success™ Naturalyte™ (contains 10g/L-1 Spinosad) at recommended field use rate (20 mL-1/L-1)
40 Diamondback larvae were then applied to each treatment block of 4 treated cabbages
Figure . Survival of Diamond Back Moth larvae on treated cabbage seedlings (16 plants assigned to each of 4 different treatments
Table. Comparative differences in DBM survival on each observation day
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Observation day
|
Significance of Difference1
|
|||||
|
Control vs EN65
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Control vs Dipel
|
Control vs Spinosad
|
EN65 vs Dipel
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EN65 vs Spinosad
|
Dipel vs Spinosad
|
|
|
1
|
NS
|
NS
|
**
|
NS
|
**
|
**
|
|
3
|
**
|
**
|
**
|
NS
|
**
|
**
|
|
5
|
*
|
**
|
**
|
NS
|
*
|
*
|
|
7
|
**
|
**
|
**
|
NS
|
NS
|
NS
|
|
10
|
**
|
**
|
**
|
NS
|
*
|
NS
|
1NS = not significant; * significant at the 5% level; ** significant at the 1% level
Control – d-10
Spinosad – d-10
Y. entomophaga - d-10
Dipel - d-10
Figure: Dry weight of remaining cabbage leaves 10-d post treatment and infestation;
Summary
- Applied as a suspension in 0.03% DuWett, Yersinia entomophaga (EN-65) provided excellent control of DBM on cabbage.
- Performance of EN-65 in a prototype formulation was comparable to the fully developed commercial Btk product, Dipel.
- Fermentation of EN-65 is straightforward and although conditions for commercial production need to be optimised, it can be economically produced.
- A gel formulation extended leaf persistence over a basic broth culture spray, while also providing higher initial deposition rates.
- Insect mortality on EN-65 gel-sprayed leaves was correspondingly higher and the toxic activity of the bacterium was preserved for longer than the broth spray.
- A gel formulation can also serve as a vehicle for inclusion of other formulation additives that may further prolong the residual activity of EN-65.
- EnCoate’s proprietary formulation techniques are likely to be highly effective in this regard.
- EN-65 can recycle within a susceptible host, with multiplication primarily occurring after insect death.
- Bt generally has only limited multiplication within an insect host.
- Replication of Y. entomophaga within an insect cadaver can provide a source of infection for larvae feeding on contaminated foliage.
- This can extend the active field life of the bacterium beyond that of the original spray application.
- This characteristic provides a route by which the pathogen can persist and spread within a host population.
