ECONOMIC ZOOLOGY — ENTOMOLOGY. 157 



days. The larva apparently does uot spin a web, but will be found on webs spun 

 by the adults. The time passed in the first nyniphal stage (protouyniph) aver- 

 aged oj days during the last of September and early October, it being divided 

 into an active feeding and a quiescent period. The protonymphs are active feed- 

 ers and their habits are similar to those of the larva. During early October 

 the second nymphal stage (deutonyniph) averaged 3i days. The deutonymphs 

 have the ability to spin webs and pass an active and a quiescent period. The 

 average preoviposition period is 3§ days, while the average obtained for the 

 entire adult stage duriug early October was 21J days. 



Notes on the general biology of the spider mite which follow deal with the 

 spinning process and use of the web. average length of life period, embryonic 

 development, molting process, parthenogenesis, sex ratios, time and method of 

 copulation, and methods of disiiersion. A somewhat extended discussion of 

 color pigments and color variation is presented in which it is shown that casual 

 observations have been very misleading in regard to color variations. The 

 author has obtained all the common color variations among the first and second 

 genei-ation descendants of a single female. Five of these individuals are repre- 

 sented in colors. 



In reporting studies of the distribution of the spider mite tables are presented 

 which show its host a-nd geographical distribution in the United States. The 

 species has at present almost a world-wide distribution. Among the regions in 

 the United States that are probably free from general infestation, the author 

 mentions the Great Plains region between the Rocky Mountains and the eastern 

 jtart of the Dakotas. Nebraska, Kansas, Oklahoma, and Texas. This region is 

 chiefly occupied either by native grasses or by field crops that are not known to 

 be hosts of the red spider. A list is presented which shows that the plants that 

 have been most frequently reported as attacked in this country are. in order of 

 the number of records obtained for each, as follows : Rose, hops, beans, violet, 

 cotton, strawberry, and tomato. 



The injury due to the spider mite is caused by its puncturing the tissues of 

 the leaves from the underside and withdrawing the liquid contents of the leaf 

 cells. Following the primary injury there is a change of color in those parts of 

 the leaves most severely injured, the change usually being simply a paling effect, 

 but there may be some reddening of the leaves, the leaves finally shrivelling 

 and dying. 



Among the more important natural enemies mentioned are an acarid (Seius 

 j)omi), which in Oregon is i^rhaps the most efiicient of any of the natural 

 enemies of the red spider; a predaceous thysanopteran {Scolothrips sexmacu- 

 latus) ; the insidious flower bug (Triphleps insidiosus) ; a neuropteran (Con- 

 ventzia hagcni) ; two lace^A^ngs (HemcroMus pacificus and CJinjsopa calif or- 

 nica) ; a cecidomyiid {Arthrqcnodax occUlentalis), the larva of which is pre- 

 daceous, which is one of the most important enemies and perhaps the most 

 widely distributed of all; a rove beetle (OUgota oriformis) which occurs in 

 citrus districts of southern California ; and several coccinellids, namely, 8te- 

 thonis picipes, 8. punctum, Scymniis nanus, and -S?. marginicolHs. A number of 

 other i)robable enemies are noted. 



Control measures are dealt with at length. Under cultural methods, the 

 author discusses clean culture, removal of infested plants, pruning and stripping 

 of leaves, trap crops, time of planting, rotation of crops, etc. Fumigation, 

 banding, and spraying are then taken up. It is pointed out that preventive 

 measures are more important and practical than remedial measures. The im- 

 portance of the destruction of useless host plants, especially those which remain 

 green during the winter, is emphasized. Clean culture is the most important 



