Team:Hamburg/Demonstrate

Demonstrate: Mosquito Experiments

Three components of our trap were tested in vivo with Anopheles mosquitoes at the Bernhard Nocht Institute for Tropical Medicine in Hamburg. First, we tested at which concentration the odor baits (lactate, 3-methyl-1-butanol and myristic acid) were most effective. Therefore, we used a Y-shaped tube, in which we placed two different baits. We compared two different substances to each other as well as comparing different concentrations of the same substance and different mixing ratios of multiple compounds. We tried to observe which of the baits were preferred over the others by the mosquitoes. To ensure the mosquitoes actively moved towards the desired bait they had to move against an air current created by a fan placed at one end of the Y-shaped tube.

Fig. 1: Experimental set-up for our odour baits test.

Prior to starting our experiments, we tested weather our presence near the Y-tube influenced the behaviour of the mosquitoes. Since they were, like before, randomly distributed in the tube, even after leaving the lab for some time, we concluded that our presence did not influence their behaviour. We tested three substances (lactate, myristic acid, 3-methyl-1-butanol) at concentrations of 1:10, 1:100, 1:1000 and 1:10000. The lure/solvent ratio of each compound differed from that in the literature, since we are aiming at achieving the same rations, that will be present in the S.H.I.E.L.D. The mosquitoes did not seem to show a preference for any of the lures. For this reason, we tried the same mixture of lures as written in the literature1. The basic ingredients are 12.5 mL lactate, 0.2 grams of myristic acid diluted in 50 mL of an aqueous solution. Because the myristic acid is poorly soluble in water we used ethanol instead. To this we added 3-methyl-1-butanol in a total volume of 1:10000. Again, the mosquitoes did not seem to show any reaction.

We noticed several error sources in our experimental setup during our first measurements. The mosquitoes were mainly sitting at the grids close to the fan as well as at sites, where the glue holds together the different pipes. The latter may be primary caused by solvent residues, which is attractant to mosquitoes. Since it is known, that heat is one of the most compelling effects for mosquitoes, the stay of mosquitoes close to the fan, which generates heat, can be easily explained. Moreover, we observed that our mosquitoes were comparatively inactive. We found that experiments with Anopheles are often performed at night, which may explain our observations.
Furthermore, the inside of the trap might be contaminated, since it was built under unsterile conditions. Residues from the human skin could have distracted the mosquitoes.

Fig. 2: Mosquitoes sitting on the grids close to the fan.

Additionally, we ensured that mosquitoes land on our hydrogel by putting it on top of a sponge soaked with a sugar solution, which is usually used to feed mosquitoes, containing 8% fructose and 4-aminobenzoic acid. The experiment failed, since no mosquitoes landed on the gel. Besides, we tried to prove the effectiveness of our insecticide by adding a sugar solution to cell lysates of our insecticide-producing bacteria and put it onto a cotton pad. Unfortunately, we were unable to show, that our insecticide leads to the death of the mosquitoes within six hours. This experiment must be definitely repeated with a longer incubation period.

Fig. 3: Recording of our insecticide tests.

In conclusion, the experiment should be repeated under different conditions. The trap should be built in a sterile environment. The wooden box which served as a coating for the fan could be replaced with a plastic one, since the wood might release an odour that is attractive for the mosquitoes. It should be tried to prevent heat production by the fan too. The experiment could be carried out at night. The hydrogel should be very thin and kept humid. It is best placed in a small cage, covered with a sugar solution. The insecticide should be tested for a longer period of time.

References

  1. ↑Verhulst, N. O. et al. Improvement of a synthetic lure for Anopheles gambiae using compounds produced by human skin microbiota. Malar. J. 10, 28 (2011).

Funding