Sublethal effects of low-dose Bt: potential for population control

Dec 05, 2020

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Sublethal effects of low-dose Bt: potential for population controlIn a four-week trial, snails were fed on alternating days with chow ('snail gel') made with (1, 10, 100, or 1000 ppm) or without Dipel Dust. 
They were good snails and always ate all their chow.
Bt had no effect on snail viability, even at the highest dose of 1000ppm = 1ppt. 
But it seems to have strongly depressed egg production. Even the snails fed on the lowest dose (1ppm) produced egg masses at less than 25% of the control rate. At higher doses, no egg masses were produced at all. We can judge that a regular diet with 10ppm Dipel Dust depresses reproductive rate by over 95%. 
This just might be a good way to knock down Biomphalaria populations in schisto-affected places!
But before we get too excited, we're going to repeat the experiment, and extend it. 

Gary, camille, and 1 other like this.

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Morgan Q. GouldingResearcher

Correction: the dose was about 0.3 micrograms per snail per day - not 30 micrograms. Darn powers of ten - if I were better at figuring them in my head I might be a millionaire instead of a thousandaire. Well, so the poison is a hundred times more potent than I thought - and might sterilize snails at a dose that doesn't actually hurt insects. Wow. Need to repeat this experiment. Extraordinary claims require extraordinary evidence.

Dec 07, 20201

Morgan Q. GouldingResearcher

PS '...according to the US Code of Federal Regulations...' (This is talking about human toxicity of pesticides!) https://www.govinfo.gov/content/pkg/CFR-2005-title40-vol23/pdf/CFR-2005-title40-vol23-sec156-64.pdf

Dec 06, 20200

Morgan Q. GouldingResearcher

PPS. Of course the median lethal dose of pesticides (for humans) is established based on experiments feeding the poisons to some other kind of mammal, rats mice and so on...

Dec 06, 20200

Morgan Q. GouldingResearcher

Dipel Dust is a commercial formulation of Bt kurstaki, a strain known to especially target larvae of lepidoptera (moth and butterfly). The label says it contains 0.064% Bt fermentation solids - all the rest is filler. ~~~ How much 'Bt fermentation solids' did each snail eat per day on average? 1.56 gdd/1000 mLsg * 0.064 gBt/100 gdd * 6.25 mLsg/chunk * 1 chunk/2 days * 1/10 snails = 3.1 x 10^-7 gBt/snail day ... So with the '1ppm' treatment, each snail ate, on average, about 30 micrograms Bt per day. ((( gdd = grams of dipel dust mLsg = milliliters of snail gel food gBt = grams of Bt fermentation solids ~~~~ Now if such a dose reduces reproductive output by more than 50%, then just how nasty a reproductive poison are we looking at? ... Estimating the snail's body weight (not counting the shell) at about half a gram, then that 1ppm dose is about 60 mg poison per kg body weight (mg/kg). ... The worst class of poison for humans, according to the US Code of Federal Regulations, is defined as 50% lethal at a dose below 50 mg/kg. ~~~~ How potent is the sterilizing effect on snails compared to the killing effect on insects? Actually not too much different. I am reading about a median lethal concentration in caterpillar food (LC50) of about 22 ppm.

Dec 06, 20200

Gary Freeman

The results are interesting. What is in Dipel Dust?

Dec 05, 20200

Molly Carle GreenBacker

Real significant progress! I will be interesting to see what happens in Round Two. Helpful that you have good snails that always eat their chow.

Dec 05, 20200

About This Project

Eco-friendly and affordable molecular weaponry against snails that transmit schistosomiasis

Bethel University, Tennessee

Schistosomiasis is a disease transmitted by snails, responsible for chronic illness of many millions of the world's poorest people, mainly in Africa. This project tests the efficacy of RNAi, a targeted genetic weapon, to kill the snails and thus curtail the spread of the disease. RNAi acts only on specific gene sequences, making it environmentally benign and preventing the evolution of resistance in snail populations. Importantly, this snail-killing material would be very cheap to produce.