Even though Nasonia is one of the most commonly collected and studied species of parasitic wasp in the world, little is known about its role in nature or its effect on blowfly populations. In a study conducted in Ontario, Canada, blowfly infestation rates did not increase as dramatically as jewel wasps' infestation rates. Researchers found the first bluebird nests in the spring contained a high number of blowflies, and the infestation rate barely increased as the bluebird breeding season progressed. Jewel wasp populations, on the other hand, seemed to build slowly throughout the season. In earlier bluebird nests, only about 2 percent of the blowfly pupae were parasitized.
Many people routinely empty their nest boxes before the onset of the next breeding season.
Sweeping the nest box contents onto the ground leaves Nasonia larvae an easy target for hungry predators, resulting in fewer wasps for next year's assault against the blowflies. For songbird enthusiasts, the first order of business is to determine whether birds do indeed prefer a nest box containing last year's nest, along with its complement of Nasonia larvae. We won't know immediately whether blowfly infestation rates decrease in groups of nest boxes where nests are routinely left intact. But constant data collection spanning a few years should begin to shed some light on the subject. And, once data are gathered from various parts of the continent, we can better determine which nest-box practices are best for cavity nesters that use nest boxes.