A total of 227, or roughly one out of every five teachers who reported to city schools for the first day of school last year, were no longer teaching in the system on Sept. 5, when the schools kicked off the 2006-07 school year. More than half of those -- 138 -- had resigned or left of their own will, and 46 retired.
Ultrasound and Arthropod Pest Control (2001), an extensive Kansas State University study, confirmed that ultrasonic sound devices do have both a repellent effect as well as reduces mating and reproduction of insects. However, the results were mixed, and ultrasonic sound had little or no effect on some pests.ome animals, such as bats, dogs, and rodents, can hear well into the ultrasonic range. Some insects, such as grasshoppers and locusts, can detect frequencies from 50,000 Hz to 100,000 Hz, and lacewings and moths can detect ultrasound as high as 240,000 Hz produced by insect-hunting bats.
ANSWER: There is limited data on how well electronic or high-frequency sound devices work for household pest control. These devices may be called ultrasonic, electronic, microvibration or electromagnetic pest repellers.The manufacturers state that they use high-frequency sound waves or electromagnetic output to repel insects (cockroaches, fleas, house flies, mosquitoes, rodents, moles, and other pests).ut rodents seem to learn to avoid the mechanisms used. Mice quickly become accustomed to regularly repeated sounds. Ultrasonic sounds have limited use in rodent control because they are directional and do not penetrate behind objects.