120 



able, as they are easily handled and the larvae thrive on them. With 

 such an arrangement the food can readily be changed and the boUworm 

 examined whenever desired. By using this method large numbers of 

 parasites were bred out at the laboratory. 



The habits of the boll worms in feeding on corn are such that they 

 are w^ell protected from parasites after the first few da3^s of their life, 

 during which time they have been boring down through the silk into 

 the ear. When once well inside the ear it is practically impossible for 

 parasites to reach the larva, unless it should leave the ear, which is 

 very rarely the case. These conditions explain the small percentage 

 of parasites shown in the following table: 



Table XL VII. — Percentages of law x parasitized on corn, 1904- 



Date col- 

 lected. 



May 15 

 May 30 

 June '1 

 June 14 

 June 26 

 July 14 

 Aug. 18 

 Sept. 10 

 Sept. 10 

 Sept. 12 

 Sept. 30 



Locality, 



Hempstead, Tex 



Dallas, Tex 



Ladonia, Tex 



Paris, Tex 



Corsieana, Tex 



Paris, Tex 



do 



Batesburg. S. C 



Pine Bluff; Ark 



Montgomery, Ala 



Paris, Tex 



Average . 



Size of larvae. 



Miscellaneous . 

 Full-grown — 

 Miscellaneous . 



Large 



Miscellaneous . 



do 



Large 



do 



Miscellaneous , 



Large 



Miscellaneous . 



Number ^^^"^^^ 

 collected. Xed. 



18 

 45 

 19 

 75 

 35 

 25 

 105 

 34 

 22 

 34 



Per cent 

 para- 

 sitized. 



































4.5 



3.0 



3.0 



Feeding on cotton, larvae are much more exposed to the attack of 

 parasites, as they must move about in search of fresh squares or bolls; 

 and even when partially hidden within a square or boll a larva is not 

 completely immune. The following table shows very clearly the 

 greater proportion of parasites on cotton as compared with corn: 





Table XLVIIL— Perc 



zntages of larvse parasitized 



on cotton 



, 1904. 





Date col- 

 lected. 



Locality. 



Size of larvse. 



Number 

 collected. 



Number 

 parasi- 

 tized. 



Per cent 

 parasi- 

 tized. 



Aug. 20 

 Aug. 25 

 Aug. 31 

 Sept. 16 



Paris Tex 



Large 



184 

 40 



104 

 13 



31 



27 



53 



9 



16.75 



do 





67.50 



do 



Miscellaneous 



51.00 



Tupelo, Miss 



Small 



69.00 



Average 













51.00 















From these data it is evident that practically one-half of the larvse 

 of the August brood are destroyed by parasites. This is especially 

 important when we recall that it is this brood which causes the greatest 

 damage to cotton. The insect responsible for this wholesale elimina- 

 tion is a small hymenopteron belonging to the family Braconidae. It 

 is more fully treated in the following pages. 



