Bacillus thuringiensis is a bacteria that can produce Cry toxin which is useful as pesticide for Lepidopteran pests. But what are the factors that can degrade or denature or reduce the efficiency of the Cry toxin on Lepidopteran pests? Temperature?pH? What about the stability of the Cry toxin?
Please advise, thank you.
The list is long. I cannot give a complete list, but I can at least start. This project will require many weeks/months at a university library to fully understand the problem and then rank the relative issues. The real problem is with "reduce the effectiveness," because that opens up a range of other possibilities.
Development of resistance. I usually think of this as target site insensitivity. However, there are a range of other options ranging from behavioral resistance (insect avoids places where the toxicant is applied), to excretion (insect does not try to metabolize the toxicant, rather it just excretes it).
Formulation issues: The formulation can facilitate or impede degradation. Formulation can be attractive or repellant and influence the probability that the insect will ingest the insecticide. Formulation influences atomization and retention (the size and number of deposits on a leaf surface) and that can influence the toxicant acquisition rate. If the toxicant acquisition rate is too low relative to nutritive value and metabolic rate, then the toxicant may only slow growth or reduce fecundity. Formulation can influence leaf carrying capacity (quantity of spray retained by the leaf before run-off. It can influence evaporation rates (changing droplet size, leaf retention, deposit structure, and ability of target to detect the deposit).
Photolysis: influenced by light intensity and wavelength.
Hydrolysis
Metabolic degradation by the target insect
Mechanical loss by wind and rain. Wind can provide abrasion either by neighboring foliage rubbing together or by blowing particulates (like sand).
In very hot environments, the Cry toxin could be denatured. I have no idea what temperature would be required. I don't recall that this is a major problem relative to other factors.
Salinity and pH could have some effect either by direct effects or through effects on insect behavior.
If the formulation influences plant quality, the insect might not feed on treated areas.
Grind: Bt is a particulate. The particle size will influence the ability of the formulation to pass through the nozzle orifice. It will also influence atomization. It might influence retention and the ability of the insect to detect the formulation.
With confirming the contents of my dear friend Timothy A Ebert . Other factors such as sunlight (UV)and even the acidity of water to suspension(more than7-8), and timing can reduce effectiveness Cry toxin of Bt.
Rasoul,
Thank you.
I thought of another issue that I neglected. Tank mixing is very important, especially with particulates. Depending on the method of agitation and tank shape, there may be calm areas within the tank. This will lead to greater variability in concentration. The effect is difficult to measure because you are breaking up a 100 liter tank into volumes less than 1 microliter. On a microliter by microliter basis there is considerable variability in concentration. This was doctoral work by Tamer Ucar. I think a search for authors Ucar and Derksen will get you close. These were two (but not the only two) authors of this work. Here is one publication:
CRITERIA AND PROCEDURES FOR EVALUATION OF SOLIDS MIXING IN AGRICULTURAL SPRAYER TANKS
Article · December 1998
DOI: 10.13031/2013.13220
T. Ucar ; H. E. Ozkan ; R. D. Fox ; R. D. Brazee ;Richard Derksen
ALSO
Experimental Study of Jet Agitation Effects on Agrochemical Mixing in Sprayer Tanks T. Ucar · H.E. Ozkan · R.D. Fox · R.D. Brazee · R.C. Derksen
Journal of Agricultural Engineering Research 02/2000; 75(2-75):195-207. DOI:10.1006/jaer.1999.0499
1. If you keep the spore-cristal complex in the growth medium several days after autolysis, cristal will be degraded by the proteases in the medium. To avoid this and you won't use the spore cristal complex immediately, keep it in 3M NaCl.
2. Heavy UV light exposure from the sun.
3. Temperature must be too high to denature the crystals. So, this is a minor factor.
4. If you are mixing a Bt product in an spreaying tank along an other agrochemical that increases pH higher than 8.5, crystals will be disolved and exposed to degradation.
Please, Jorge,
can you explain how muh is "too hight" temperature for denature the crystals. Is because I had read that in some reviews that the complex is sterilizated by autoclaving for crystals uses after that.
Thanks
Another thing to consider is whether the question is about field efficacy or storage, and whether this is a question about normal field efficacy versus how far can I push the limits.
One could store the formulation in a small tin shed in full sun, and temperatures in such a shed might get quite high on a hot day in the tropics. One could consider the problem of spraying a field and having a couple hundred gallons left over. Will the spray still be effective if I leave it in the spray tank for two weeks, or could I add 1/4 rate to bring the tank back to full strength? From a research perspective, you always want to use fresh material and you always want to make sure that while the product is in your possession that you adhere to the label recommendations. If the label states do not store above 30 C, then you should get new product if storage conditions exceed this value. No one benefits from starting with a sample of pesticide that is not typical of that produced by the manufacturer unless the whole point of the study is to look at degradation effects
The title of this article seems relevant, but I don't have easy access to the article.
http://www.library.biophys.msu.ru/gettext?Serial=76335.