NO. 1310. NOR TH A MERICAN THYSA NOPTERA—HINDS. 115 



is passed in some secluded place, pup* being found in the loose soil 

 ; about the base of the plant, in the leaf sheath, or some similarly pro- 

 tected place, and many have been recorded as transforming in galls. 

 .When these changes have been completed, another molt takes place and 

 the adult emerges. 



The most noteworthy points in the metamorphosis may be summa- 

 rized as follows: The larva reseml)les the adult in general form and in 

 mouth parts; wings are developed in external sheaths; the transitional 

 stage between larva and adult is quiet, and during it no nourishment 

 is taken. The metamorphosis is therefore intermediate between com- 

 plete and incomplete. 



//^7v6'r;?«?'/o//.— Thysanoptera pass the winter in either larval, pupal, 

 i or adult stages. Many species, without doubt, hibernate in very nearly 

 the same places in which they have fed. The bark-inhabiting forms 

 remain in such places, together with many of the leaf forms' which 

 migrate onto the trunk. The dried stems of flowers and grasses shel- 

 ter many species, while many of the leaf -inhabiting forms fall to the 

 ground and are among those which may be found under fallen foliage, 

 in moss, etc. Lichens and fungi shelter some as winter guests, while 

 [dead grass and turf contain many forms. It appears very probable 

 that some of the larvae which have been found upon the roots of 

 plants were hibernating there rather than feeding thereon, as has been 

 ■supposed. 



I The hibernating individuals appear to be able to withstand extreme 

 degrees of cold and moisture. I have brought in a number of species 

 gathered by pulling the frozen grass from bare mowings in midwinter 

 after a temperature of -21- F. Upon being l^rought into a warm 

 room, they very soon became active and ran about. 

 ' Thrips emerge from hibernation very early in the spring, and as 

 ^oon as their normal food plants begin to grow most of them are in a 

 condition to deposit eggs for a new generation, which in some cases in 

 Massachusetts hatch during the latter part of April or the tirst of May. 

 ' Length of Ufe.~YQ\f observations have been recorded upon this 

 point, but it seems improbable that even the longest lived exceed a 

 ,mgle year. Among those species which produce several generations 

 n a season, the hibernating individuals must live for at least seven 

 nonths in the northern United States while the summei- generations 

 ire nmch shorter lived. Their age however, as a rule, considerabl3\ 

 exceeds the length of the life cycle, for oviposition is a slow process, 

 ind in Ana2)hothr{2Js striatm is known to extend over a period of 

 ^ve or six weeks. As a result of this there is an indistinguislia))le 

 )verlapping of broods. I have kept a female of a midsummer gen- 

 eration of .1. striatus confined in a bottle in the laboratory for almost 

 Ive weeks. This species has eight or nine generations in u season. 

 :nd may therefore be expected to be one of the shortest lived in 

 ummer. 



