GREENHOUSE RED SPIDER. 157 



able to withstand the attacks of this pest. Nearly every cucumber grower 

 in the Boston district, so far as the writer has been able to determine, is 

 forced to fight red spiders in order to bring his crop to maturity. In many 

 cases vvhole houses of j'oung cucumber plants have been destroyed with 

 sulfur fumes because the mites were so numerous and the injuries so 

 severe that it was deemed wise by the grower to destroy the plants and 

 reset the house. The usual methods used by greenhouse men to combat 

 this pest consist of severe pruning of infested plants and spraying with 

 as strong a stream of water as these delicate plants ^vill stand, repeating 

 this as often as possible without allowing mildew to seriously injure the 

 leaves. In nearly all cases the mites whi out m the struggle for existence, 

 and shorten the life of a cucumber plant over one month. Under normal 

 conditions the plant should betir a large amount of fruit during this time. 

 The loss, therefore, to cucumber men by red spider infestation is due to 

 shortening the life of the plant during its productive period. 



A conservative estimate of the value of the cucumber crop grown 

 within the market-garden district of Boston is $1,500,000 per season. 

 The cucumber growers suffer a loss of approximately $150,000, or 10 per 

 cent, of the whole crop, from the ravages of the red spider alone. Many 

 individual growers have estimated their loss between $2,000 and $5,000 

 annually. 



LIFE HISTORY. 



An examination of infested cucumbers will reveal the presence of tiny 

 transparent eggs, resembling minute dewdrops, attached to the under 

 surface of a leaf or interwoven among the silvery threads which the mites 

 are capable of spinning. In developing from the egg to the adult stage 

 the red spider follows one of two distinct courses, depending on the sex. 



With the female the egg hatches in about four or five days to a tiny 

 colorless, six-legged form known as the larva, which feeds actively for a 

 little over one day. At the end of this time the larva becomes firmly 

 attached to the leaf and enters a quiescent premolting period which lasts 

 for one day. At the termination of this time the skin is shed and there 

 appears an eight-legged form called the primary nymph or protonjrmph, 

 which feeds for approximately one day and then enters a quiescent pre- 

 molting period. The duration of this period is approximately the same as 

 that of the larval quiescent stage. From this premolting period there 

 emerges the secondary nymph or deutonymph, which is probably the 

 most voracious of the immature mites. The deutonyinphal stage is 

 divided into an active feeding period and a quiescent period, each of 

 which requires one day for its completion, after which the adult female 

 emerges from the deutonymphal molt. For the development from egg 

 to adult it takes seven to eight days under favorable conditions of tem- 

 perature. (See table on page 159.) The stages of the female red spider 

 and their duration may be represented as follows : — 



v„,r To,-rro Quiescent Proto- Quiescent Deuto- Quiescent aj u o 



i.gg. l.arva. j nymph. II. nymph. III. ^d"'* ?" 



I 1 1 1 1 1 1 H— 1 



4-5 days. 1}^ days. 1 day. IH days. 1J4 days. IJ^ days. 1 day. 15-20 days. 



