Plans to use genetically modified mosquitoes to rid the world of malaria, dengue, yellow fever and zika have faltered after officials admitted that a major pilot had not worked.

Oxitec, the British company that was originally a spin-off from Oxford University, engineered a line of insects whose offspring could not grow into adults, causing the population to crash.

Millions of the mosquitoes were released at the British Overseas Territory of Grand Cayman over the past two years, but last week Dwayne Seymour, the environmental health minister, admitted that “the scheme wasn’t getting the results we were looking for” and would not be continued, with the contract formally ending on Dec 31.

The Mosquito Research and Control Unit on Cayman was concerned that it could put islanders at risk as it was feared that the approach could make diseases worse by reducing immunity, as well as spreading antibiotic-resistant bacteria.