When might fumigation be necessary for controlling wood wasps?

Fumigation is particularly necessary for controlling wood wasps when continued emergence becomes a problem. This situation indicates that wood wasps have successfully infested a structure, and there is ongoing activity, signaled by their emergence from the wood. Fumigation is a comprehensive pest control method that penetrates wood materials effectively, targeting pests that are difficult to manage through other means.

When wood wasps have established significant populations, they can cause substantial structural damage over time. Addressing the issue promptly through fumigation helps to eliminate not just the adult insects that might be emerging but also the larvae embedded within the wood, which could lead to further infestations.

The other options do not align with the primary context where fumigation is warranted. For instance, fumigation is not typically needed simply because wood wasps invade gardens or are found in outdoor wood, as these situations may not involve the level of infestation or damage that warrants such an intensive treatment. Preventing initial infestations is generally managed through other strategies like monitoring and using preventative treatments, rather than fumigation, which is more reactive in nature and applied after an infestation has been confirmed to avoid further emergence issues.