I would like to conduct an experiment about contact and fumigant toxicity of some essential oils. I plane to use 5 different concentrations with five replications for each concentration. Then determine the LD50 after 24h.The number of insect will be 20 individuals per vial. I would like to use the same experiment to determine the lethal time LT50. My main problem is how to record the data for both parameters with one experiment.
Hi Mr Hamada Chakira,
You can use in this kind of studies : a design of experiments including one factor at 5 levels (Fumigant applied concentration), and 2 response variables (number of dead insects for each applied concentartion) and (lethal time recorded in each vial). After mathematical modeling of your two responses using DoE software, you can choose predict points in the responses surface or optimization to find wich concentration of fumigant causes 50 % insect death (LD50) at wich corresponding time (LT50);
Hi Hamada
Since the LT50 is normally measured using a single discriminating dose you could use your experiment to determine a measure. What you need to do is make more observations of outcome, and with essential oils I suggest you make those every 10 minutes for the first hour, then reduce the frequency to maybe every 20 minutes over the next 1-2 hours and after that once each hour.
I expect you will find some difference in the extrapolated LT50 with each concentration of essential oil (after correcting for concentration effects of course) because there will be more than one factor involved in development of the killing effect with EOs - solvent action, neurotoxicity, enzyme decoupling, etc. The relative balance of these effects depends upon the EO used and what proportion of terpenoids occur in it.
If you are just performing a single experimental approach to evaluate fumigant and contact effects together how will you distinguish between these? Insects in a tube, even in contact with a treated surface, may be more influenced by the vapour if the EO is highly volatile and this may have a different physiological effect from exposure on an "open" surface where contact rather than vapour is the primary route of entry into the insect.
Testing EOs in vitro is not the same as testing non-volatile neurotoxic insecticides. So I think you need to take some care in the interpretation of your results. Mortality is one factor. The mode of action is another. If it is the case that your EO has more thna one MOA you are likely to have some distinctive differences in both the LD50 and LT50 across your dose concentration range.
Regards, Ian
Hi Tarek Moussaoui and Ian F Burgess.
Thank you very much for your userful answers. I will take in acoount your suggestions. I realise that the formulation of my question may leads to confusion , as stated Mr Ian F Burgess. In fact the two experiments contact and fumigant will be conducted separatly. Thus in both experiments I will need to determine LD50 and LT50.
I take the oportunity to ask tone more question related to the experiment:
In the fumigant toxicity experiment , I realise that 24h is already long time for the insect ( green rice leafhopper) not to eat. So, I plane to introduce small plant seedling in the apperatus but I am still in confusion if the presence of the plants will or not affect the result. I read papers. Some authors put nutritions while performing this experiment , some dont mention they put. One paper used tomato leaves as nutrition in the fumigant toxicity on whitefly. Thus I would like your suggestion for this question of put o not put the rice seedlin as nutriti in the fumigant toxicity experiment. Additionly, I will be pleased to receive any further information, document and software related to the experiment. Sincerely
I do not think the plants will affect the result. In fact I believe the plants will provide a more practical and useful result because if this essential oil is to be used to control the insects in the real world (not just in an academic laboratory experiment) there will be real plants present. So If the plants have some effect you will find the true LD50 and LT50 for practical use and if the plants have no effect it makes no difference to the outcome.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts