40 MASS. EXPERIMENT STATION BULLETIN 398 



by the plant bug, Lygus campestris L. Typical injury resulted from the punc- 

 tures by the bugs in the heart and new stalks of the celery. The punctures were 

 usually infected with a bacterial or fungus rot which turned the heart black, 

 making the celery unfit for sale and often useless for any purpose. Reports from 

 growers indicate that spraying with powdered derris and a wetting agent, prepared 

 bj' the formula recommended for spra\ing to combat the European corn borer, 

 is helpful and will give satisfactory control if the applications are started while 

 the infestation is light. 



The Effects of Solar Heat on the Subcortical Development of Elm Bark Beetles. 



(W. B. Becker.) In addition to laboratory and field work with Hyliirgopinus 

 rufipes in Amherst, field work with this species was also carried on in Pittsfield 

 this summer. Work on Scolytus multistriatus was carried on in Springfield and 

 Westfield. 



Two brief tentative observations on the trend of the field work may be given 

 now. (1) Freshly cut elm logs, not 3'et infested with the beetles, which were 

 placed (in the early spring) in a north-south position where the sunlight could 

 strike them all day, did not seem to become infested with any elm Scolytids on 

 most of the uppef half throughout the season. This applied to logs up to 4 feet 

 4 inches in diameter with bark up to 2 3/16 inches thick. (2) When Scolytid 

 beetles were already in the bark before the logs were placed in the sun, the mor- 

 tality due to the high subcortical temperatures generated by the sun's rays varied 

 with the thickness of the bark, mortality being highest and including a broader 

 arc of the upper surface in logs with thin bark. Some factors to be considered 

 in this work are the weather, thickness of bark, and diameter of logs, as well as 

 the effects of heat on different species of bark beetles. 



Some New Findings of Scolytus multistriatus Marsham in Massachusetts. 

 (W. B. Becker.) This species was found to be abundant at a locality in Spring- 

 field and was also found in Pittsfield. Federal scouts attached to the office of 

 the Bureau of Entomology and Plant Quarantine at Bloomfield, New Jersey, 

 uncovered infestations in Williamstown and North Adams. 



Insect Pests of Wood and of Shade, Forest, and Ornamental Trees in Mass- 

 achusetts. (W. B. Becker.) During the year, 249 inquiries were received about 

 such insect pests, involving 72 species. Ants, termites, powder post beetles, 

 aphids, oak twig pruners, Japanese beetles, and secondary tree-boring insects 

 were received most frequently. 



DEPARTMENT OF FLORICULTURE 

 Clark L. Thayer in Charge 



Breeding Snapdragons for Varietal Improvement and Disease Resistance. 



(Harold E. \\'hite, Waltham.) Two t>'pes of resistance to rust have been observed 

 in snapdragons. The first is inherited as a simple dominant factor which has been 

 reported previously. The second is a modified dominant type obtained from 

 progeny of crosses made with susceptible commercial varieties. The most promis- 

 ing rust-resistant strains are those developed by inter-crossing susceptible com- 

 mercial greenhouse forcing varieties. These strains are 80 to 100 percent resistant 

 to rust, free flowering in winter, and good seed producers. The plants can be 

 propagated from cuttings and such material has been highly resistant to rust 

 for three seasons in field and greenhouse tests. 



