1. The pear borer is widely distributed in the eastern part of this country. 2. The abdominal cavity of the female was filled with eggs. 3. The incubation period of the eggs averaged 5.6 days at a mean temperature of 76.2 degrees F. 4. The larvae fed mainly on the inner bark and cambium of the trees, but occasionally burrowed slightly into the sapwood. 5. There were six larval stages. 6. Larger larvae devoured smaller larvae on contact with them. 7. Around 85 percent of the borers have a one-year life cycle. 8. The winter was passed by the larva in a silken hibernaculum constructed in the burrow. 9. The pupa was strongly chitinized, and the abdomen was armed with large spines. 10. The pupal stage averaged 23.0 days for the males and 17.44 days for the females. 11. The moths were most active and most of the eggs were deposited between 2:00 and 4:00 p. m. 12. On the female moth there was more yellow than on the male. 13. The average length of life for the males was 4.46 days and for the females 4.96 days. 14. In the andrews orchard 50 to 100 borers per tree were not unusual. 15. The apple is the main host plant of the larvae in Virginia. 16. About 99 percent of the moths emerged between May 15 and July 10. 17. The male moths emerged several days before the female. 18. The females had deposited 33 percent of thelr eggs when they were captured in the bait-pails. 19. The pear borer is sometimes rather extensively attacked by hymenopterous parasites. 20. The borers may be removed with a sharp hawk-bill knife in the fall or early spring. 21. In heavily infested orchards, bait-pails would be economical and quite effective in reducing the number of moths present in the orchard during May and June. 22. The common insecticidal sprays are not effective in killing the larvae. 23. Paradichlorobenzene dissolved in cottonseed oil, white mineral oil, and pine tar oil and applied to the trunks and larger limbs of the trees with a paint brush gave excellent results without injury to the tree. / Master of Science