THE EED SPIDER ON COTTON. 



17 



of eggs and developed individuals of both sexes in the usual propor- 

 tion. Since ordinarily these virgin females would have deposited 

 eggs producing males, it is demonstrated by the equal representation 

 of female progeny in such matings that the parthenogenetic male is 

 completely potent. 



Parthenogenesis has a very important role in the biology of the 

 common red spider. Earlier writers have shown that it works to 

 maintain a relative equilibrium between the individuals of the sexes. 

 Migrating females very frequently estabhsh themselves without hav- 

 ing been fertilized, and they are very Kkely to be without males 

 subsequently. Thus in the event that they arrive unfertilized, their 

 offspring will all be male, and upon the maturing of these male broods 



Fig. 5. — a, Cross section of normal cotton leaf; b, cross section of cotton leaf injured by tlie red spider. The 

 puncture is near lower right-hand comer. Highly magnified. (McGregor.) 



the "pioneer" females will at once begin laying fertilized eggs, which 

 will maintain the sexes nearly even. 



Feeding and injury to plants. — All stages of the red spider, as 

 before stated, feed actively upon the leaf of the host plant. The 

 focfling operation is accomplished by means of sliarp, slondor, lance- 

 liko mouth parts whicli arc tlirust through the epidermis well into 

 the leaf, usually on the underside. In the case of cotton, which is 

 typi<-al, tlie punctun; is mad(! through tlie underside. Tlio conse- 

 quent siphoning out of tlie ccsllular material in the immediate 

 vicinity of the puncture results in the impoverishmc^nt of tlie imme- 

 diately udjacf!nt tissue (see fig. 5). The parenchymal cells are 

 r,4:jw''— r.uii. 4if>— 17 3 



