459 



are as beneficial as they are injurious to vegetation whenever plants 

 are competing among themselves for space in which to grow. Neither 

 can any insects be classed as obnoxious to man, as it may easily be 

 that a large number of human beings will be benefited by the 

 misfortunes of a small number. 



Cory (E. N.). Fumigation of Greenhouses. — Maryland Agric. Expt. 

 Sta., College Park, BuU. no. 205, April 1917, pp. 264-282. 

 [Received 7th August 1917.] 



This paper gives detailed instructions for fumigating greenhouses. 

 The results of experimental fumigation on various insects are shown 

 in tables. 



The second part of the paper discusses fumigation with special 

 reference to humidity and temperature and gives the results of 

 experiments in fumigation under various conditions of heat and 

 moisture. Night was found to be the best time for the process. Definite 

 doses may be recommended under optimum conditions of heat and 

 moisture for different plants, and under normal conditions for various 

 insects. Slight reductions in the doses may be effected by increasing 

 the temperature to a maximum of 70° F. without injury to plants, 

 if the humidity is kept at or below 50% saturation. High moisture 

 is certainly liable to produce injury to plants, but both high moisture 

 and high temperature will increase insect mortality if the dose is 

 below the optimum for the insect concerned. When possible, plants 

 other than stove plants should be fumigated at night with the 

 optimum dose for the insect, with a temperature at or below 50° F, 

 and with the atmosphere about half saturated. 



Cory (E. N.) & O'Neill (F. H.). The Hothouse milipei.— Maryland 

 Agric. Expt. Sta., College Park, Bull. no. 206, April 1917, 12 pp., 

 3 figs. [Received 7th August 1917.] 



Reports of injury attributed to Oxidus gracilis, Koch (hothouse 

 millipede) led to the investigations recorded in this bulletin. Though 

 probably of tropical origin, 0. gracilis has apparently been introduced 

 into the United States from Europe. Under normal conditions it 

 appears to have only one generation a year. The various stages are 

 described. Manure and decaying vegetable matter form its principal 

 food. Dead leaves lying on the soil are also eaten after they become 

 moist, the midrib and larger veins being left. Experiments seem to 

 show that millipedes will not burrow in sand after the raw ends of 

 cuttings or newly formed roots and mil not attack the stems of plants 

 even under the stress of hunger, while they can subsist for some time 

 on the humus in the soil. Germinating seeds are sometimes attacked. 

 It is believed that millipedes can be starved into attacking the roots 

 of some plants and under certain conditions may damage them to a 

 limited extent. Some instances of predaceous habits are given, 

 among the victims being a green Aphid. Circumstances point to a 

 centipede as a possible natural enemy. 



Bait-traps, made by placing slices of potato or carrot in a small 

 depression covered with a flower-pot, are useful, or a hole may be cut 

 in a potato and the tuber buried in the soil. Tobacco products are 

 probably the best material for controlling 0. gracilis. Tobacco dust 



