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Growth Medium

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Fungi that attack insects such as mosquitoes are being developed as biological control agents. However, in spite of the environmental benefits of using living fungi as biological pesticides, few have been successfully commercialized due to inconsistent results compared with chemical insecticides. This is because the fungi do not survive long in sunlight due to ultraviolet (UV) radiation.

Researchers are attempting to genetically engineer the fungi to be more resistant to UV. This could lead to a powerful new way to control mosquitoes. Researchers have added a gene from a bacterium that is resistant to UV damage to the fungus.

Study 1

Spores of a fungus were genetically modified with a gene that helps to repair DNA that has been damaged by UV light. Then spores of both the original wild type (WT) and the modified transgenic strain (TS) were exposed to sunlight and the amount of damage to their DNA was measured.

Study 2

Next spores of both types were exposed to sunlight for varying lengths of time and the percent of the fungus spores that germinated after 24 and 48 hours were recorded.

Length of Solar Exposure (hrs) Wild Type Germination Rate % Transgenic Species Germination Rate %
2 100 100
4 48.8 56.0
6 4.6 45.2
7 1.1 35.4

Study 3

Finally spoors of each type were mixed into a liquid medium and exposed to sunlight for 7 hours. The mixtures were then sprayed on separate groups of mosquitos and the rate of survival was monitored over a 2-week period. Pure growth medium was sprayed on one group of mosquitoes as a control.

Tables and figures adapted from Fang W, St. Leger RJ (2012) Enhanced UV Resistance and Improved Killing of Malaria Mosquitoes by Photolyase Transgenic Entomopathogenic Fungi. PLoS ONE 7(8): e43069. doi:10.1371/journal.pone.0043069

Which of the following would be the best explanation for why the researchers sprayed growth medium without fungi on the mosquitoes in Study 3?

A

The researchers wanted to have a group that would allow fungi to transfer to the mosquitoes.

B

The researchers wanted to know the survival rate of the mosquitoes that had been sprayed but had no exposure to fungi.

C

The researchers wanted to the see what would happen to the growth rate of the fungi that naturally live on the mosquitoes.

D

The researchers wanted to make sure that any fungi on the mosquitoes was eliminated before they added the test fungi.