30 Director's Hepokt of the 



content of the body is low and the insects are comparatively inactive. 

 It is possible that the spiracles are partially closed, which would 

 also lessen the effect of the gas. A rise in temperature is correlated 

 with greater effectiveness, but this increase in the deadly properties 

 is more apparent between fifty and seventy degrees than at lower 

 temperatures. A dry air is not favorable to fumigation with cyanide 

 when the insects are in a hibernating state, which suggests that 

 the low moisture content which usually accompanies this condition 

 is one of the factors that help modify the effect of the gas. 



The pear psylla. — Circular 20 from this department is a popular 

 treatise, illustrated with two plates and a number of text figures, 

 on this species of psylla, which is regarded as one of the principal 

 enemies of pear orchards. The different life stages are described 

 and figured, and seasonal history discussed. Attention is directed 

 especially to the habits of the hibernating adults during the late 

 fall, winter and early spring and to their activities during the period 

 of oviposition. Detailed instructions are given for a number of 

 spraying practices which are directed to the killing of the hibernating 

 flies to reduce the extent of oviposition, and to the destruction of 

 eggs and the first-brood nymphs. 



The false tarnished plant-bug. — Circular 21 calls attention to the 

 work of this insect, which has been very troublesome to pear-growers 

 in certain localities in western New York. A brief account is given 

 of the life history and habits of the pest. The circular concludes 

 with short spraying directions for the prevention of injury. 



The control of plant lice on apple trees. — Circular 23 is a short 

 memoir, dealing with the more destructive species of plant lice 

 attacking apple trees. An account is given of the habits of the 

 insects which are responsible for injuries to foliage and fruit and 

 general suggestions are given for the protection of bearing orchards. 



Apple insects. — Circular 25 deals with the following insects: 

 Pistol case-bearer, cigar case-bearer, bud moth, oblique-banded 

 leaf-roller, fruit tree leaf-roller, apple red-bugs, green fruit worms, 

 codling moth, lesser apple worm, palmer worm, plum curculio, 

 tussock moth, apple maggot, gipsy moth and browntail moth. 

 A brief life history is given of each and concise directions for treat- 

 ments. The memoir concludes with a spraying calendar, with instruc- 

 tions for the application of lime-sulphur as a general insecticide. 



