I learned this fact on, of all things, The Dr. Oz Show: Bug zappers aren’t very effective at killing mosquitoes, and also kill many beneficial insects such as moths, bees, and beetles. The episode was about staying safe and comfortable during the hot summer months. The reason bug zappers don’t work well against mosquitoes is that UV light does little to attract the little blood-suckers, but is highly attractive to other insects. Newer “zapper” models that use carbon dioxide as an attractant work better, but cost hundreds of dollars.
Read more about how bug zappers kill beneficial insects.