46 BULLETIN 416^ V. S. DEPARTMENT OF AGEICULTURE. 



Table XVI. — Rate of destruction of red spiders by the larva of Chrysopa rufilabris — Con. 





Hatched. 



Red spiders consumed. 



Pupated. 



Length 



of 

 larval 

 period. 



Feed- 

 ing 

 days. 





Larva 

 No. 



13th 

 day. 



14th 

 day.. 



15th 

 day. 



16th 

 day. 



17th 

 day. 



18th 

 day. 



Total 



for 

 larval 

 period. 



Total 



feeding 



days. 



1 



1914. 

 July 17. . . . 





















1 

 6 

 7 



18 

 3 

 7 

 8 



10 

 9 

 6 

 2 

 4 

 5 





2 



July 18.... 







i " " 















3 



do 























4 



Aug.3.... 

 Aug. 8 



77 



99 



110 



224 



119 



198 



1,250 



Aug. 22... 



18 





6 



July 15 























7 



July 16. . . . 





















[ 86 



8 



Julvigi.. 

 do.i... 



75 

 58 

 80 



101 

 117 

 106 



113 



147 

 130 



199 



220 



156 



122 

 116 



170 

 127 

 129 

 130 



203 

 207 

 211 

 188 

 193 

 208 





July 30. . . . 







9 



Aug. 29. .. 







10 



Aug. 222.. 

 Aug. 18 3.. 



. ..do 







11 





Aug. 21 







12 



Aug. 14 4.. 







145 

 129 



189 

 219 



Aug. 19. .. 







13 



Aug. 20 2.. 





98 



Aug. 26. .. 















1 Collected as half-grown larva. 



- Collected as two-thirds growTi larva. 



3 Collected as mature larva. 



4 Collected as large larva. 



In summarizing Table XVI it is found that 6,956 adult red 

 spiders were consumed by 13 Chrysopa larvae in 86 feeding days, or 

 an average daily consumption of about 81. The one larva for which 

 complete data are recorded consumed altogether 1,250 mites. The 

 largest daily feeding was 224 mites. As the larva grows the appetite 

 increases remarkably so that an individual which ate only 20 mites 

 per day following hatching will consume ten times that number just 

 prior to pupation. Larvae numbers 8, 9, 10, 11, 12, and 13 were 

 collected in the field in various stages of maturity, so that only the 

 feeding of the final days can be shown. It is probable that the 

 figures consistently represent the normal activity of this species 

 as a red-spider eradicator. The appetite for mite eggs was not 

 determined, but we have often seen larvae in the act of devouring 

 them. Probably numerous eggs were eaten along with the mites in 

 aU the foregoing records. Three minutes appears to be the average 

 time required by larvae in devouring a mite. 



We have followed the process of the fabrication of the cocoon of 

 Chrysopa rufilabris from beginning to end. Working in a looped 

 attitude, the successive layers of silk are secreted from the tip of the 

 abdomen, which is moved shuttle-hke from side to side. Contrary 

 to long-accepted belief, it has been established that the circular lid, 

 which permits the exit of the adult fly, is prepared by the larva as 

 the last act before entering the resting stage. 



During the four seasons of our investigations at Batesburg it has 

 been determined that a considerable percentage of mortality to 

 chrysopids arises through parasitism. The results of a series of 

 studies on lacewing-fly parasites has been published. (McGregor, 

 1914.) In a series of 99 cocoons collected in the field, 48 yielded 



