Insecticide in Cockroaches Report Writing – Medical Science Assignment Help

Assignment Task

Task

Introduction:

A spray can of pesticide is a common item found in many Sydney households. Before these products are approved for the consumer market, they must undergo rigorous toxicological testing. The LD50 is a common method used to evaluate the toxicity of a substance and this involves determining the concentration that causes fatality in half of the test population. A range finding assay is usually carried out with a wide range of concentrations to estimate the LD50. The aim of this experiment is to determine the LD50 of the carbamate insecticide propoxur on American Cockroaches (Nymph stage of the life cycle).

PART 1: Range Finding 

The technical staff have carried out the first part of this experiment to provide a rough estimate of the LD50 (range finding). Stock solutions have been prepared to specifications to allow a definitive LD50 to be determined. As an exercise, students must carry out the calculation required to produce this stock solution.

Question 1: How many grams of technical grade insecticide (propoxur) are required to produce 25 mL of 1% w/v stock solution?

Question 2: As a practice exercise for your report, you will need to transform the range finding data. You will also need to construct a Log-Dose response curve and a Probit curve. The graph paper is attached in the appendix. What is the outcome of the range finding if it is converted into average deaths per dose and transformed into a percentage of fatality?

PART 2: Determination of LD50: 

Preliminary studies have shown that the range for the LD50 is between 0.01% w/v and up to 0.1% w/v. This was confirmed from the range finding results prepared by the technical staff. Now you must choose 4 or 5 concentrations around the LD50. You are aiming to have concentrations of insecticide that will kill between 15% and 85% of the test population. In practice choosing the range for the definitive LD50 determination might take a number of test runs. Unfortunately due to time constraints you are advised to discuss the concentrations you choose with the demonstrator. Bear in mind they need to be concentrations that can easily be made by dilution of the stock solution.

The following tasks should be allocated to the members within your group. These tasks do not have to be carried out in order but simultaneously. We have provided this guideline in order to improve the efficiency of your group work but as 3rd year students you are expected to be competent for self directed research work.

Task 1: Preparation of Plastic Cups:

Each group must prepare the plastic cups that will contain the test population of cockroaches. Each plastic cup will contain 5 cockroaches for this experiment and must be painted with fluon to limit escape. The following images are provided to demonstrate how the cup should be prepared. Once the cups are done, you must label them with your GROUP NAME, DATE, INSECTICIDE and DOSE CONCENTRATION. You will need to prepare a total of 11 cups for this experiment, 10 for duplicate tests of the 5 doses and 1 as a TRANSFER medium.

Task 2: Selection of Sample Cockroach Population: 

Each group must now select the cockroaches required for this experiment. You should follow the selection guidelines as close as possible as the LD50 is related to the size of the target. Each group has been provided with a beaker of mixed age cockroaches and a tub of crushed ice. If the selection of cockroaches is difficult, then place the beaker in the tub of ice and slow them down.

Task 3: Preparing Dilutions of Propoxur:

The third task requires each group to prepare the dilutions of propoxur required to dose the test population. A 1% w/v propoxur stock is provided by your demonstrator and is the starting solution for each of your dilutions. You must now do some basic maths to complete the following table. The doses used in this experiment are standardized for each class.

Micropipettes (100itL – 1000pL) are provided on your benches and a dispenser (EMK) fixed at 9mL provided in the fume hoods. You must construct each of these dilutions using two steps to minimize error. This can be achieved by using either a combination of 2 aliquots from the micropipette, or 1 aliquot from the micropipette and a 9mL fraction from the dispenser. It’s not necessary to have the same total volume as long as the dilutions are constructed to specified concentrations. You should also attempt to make the maximum volume of dilutions that can be achieved with the equipment you have.

Task 4: Application of Insecticide:

The final task requires the application of the insecticide doses to your test population. This will utilise the micro-applicators in the fume hood and your demonstrators will show you how to use them.

Before applying the insecticide, the applicator needs to be rinsed with EMK to remove residual substances. You must wash with EMK twice followed by a wash with the solution you are about to use. Repeat this wash process for each subsequent solution that you will use; however it’s sufficient to wash once with EMK instead of two. The following images will demonstrate the dermal application of insecticide to the cockroach abdomen.