Final answer:
Based on provided data, while exact figures for the Galapagos Islands' insect fauna are not specified, comparison with Hawaiian and Florida data suggests that less than half are invasive, and hence the best estimated answer is 1/4.
Step-by-step explanation:
The question, 'More than what fraction of the total insect fauna has been registered as invasive species in the Galapagos?' is inquiring about the proportion of insects in the Galapagos Islands that are considered to be invasive. According to the information provided, in the Hawaiian Islands 25% of insects are introduced species, and for Florida, it is 8% of insects. Although the exact figures for the Galapagos Islands are not provided within the reference, no quantities mentioned exceed half, suggesting that the answer is most likely less than the options provided of 1/2, 3/4, or 4/5. Therefore, by deduction and without exact figures for the Galapagos, the best estimated choice from the provided options would be 1/4 (option 1).