Which type of synthetic insecticide is considered to have low toxicity and is effective against wood-destroying fungi and insects?

The correct answer is borates because they are a type of synthetic insecticide known for their low toxicity to humans and pets, while effectively targeting wood-destroying fungi and insects. Borates work by disrupting the metabolic processes of pests, making them less likely to develop resistance compared to other insecticides.

Borates can be applied as a treatment to wood and soil, helping to protect structures from various wood-destroying organisms. They are particularly valued in pest management due to their safety and effectiveness, especially in comparison to more toxic alternatives.

In terms of the other options, while pyrethrins are effective against a variety of pests, they can have higher toxicity levels and are often derived from natural sources, which does not align with the synthetic aspect mentioned in the question. Diatomaceous earth is a mechanical insecticide that works by physically damaging the exoskeletons of insects, but it does not directly target wood-destroying fungi. Neonicotinoids are notorious for their toxicity to beneficial insects, particularly pollinators, and while they can be effective, their overall safety profile compared to borates is less favorable.