Are there international guidelines or regulations for field trials of GM mosquitoes or can countries impose their own regulations?

Regulations for the release of GM organisms of any kind in a country are covered by the national (biosafety) regulations and law of that country. Each country has its own regulatory procedures although in practice many countries adopt similar processes and standards, including a risk assessment. The Cartagena Protocol on Biosafety is an international treaty governing movement of GMOs between different countries. It was adopted on 29 January 2000 as a supplementary agreement to the Convention on Biological Diversity and entered into force on 11 September 2003. Over 160 countries have agreed that they will put systems to implement it through their national laws in place.

There is now also a growing body of guidance on GM insects from regulatory bodies around the world such as the World Health Organisation, the European Food Safety Authority and the North American Plant Protection Organisation

Further reading:

The Cartagena Protocol

EFSA Guidance on Environmental Considerations for GM animals

WHO Guidance Framework for testing genetically modified mosquitoes