may have been due to one or more of three causes: (1) that the soil 

 used in the experiments contained the disease to an extent above 

 normal; (2) that the confinement produced a predisposition to the 

 disease through mechanical injury, since it is supposed to require 

 an abrasion of the skin in order to permit the bacteria to gain access to 

 the grub's body; or (3) that excessive humidity in the boxes was 

 favorable to the progress of the disease. 



The fifty-nine grubs that died in experimental boxes apparently 

 as a result of the bacterial disease were divided into four groups, as 

 follows : 



(1) Grubs with sure sigus of infection, that died while still iu the larval 

 stage. 



(2) Grubs with lesions, or other signs of the disease, that reached the pupal 

 stage and then died. 



(3) Grubs with lesions or other signs of disease that died, but were also 

 infected with Metarrhizium fungus, so that the exact cause of death was uncertain. 



(4) Grubs that showed a characteristic blackening of segments after death, 

 but of which no previous symptoms had been noted. 



Of these four groups, forty-five of the grubs fell in tlie first, 

 four in the second, six in the third, and four iu the fourth. 



Some idea of the progress of this disease, prior to death of the 

 grub, may be gained by the following records of ten individual 

 infected grubs: 



(1) Jan. 18. — Lesion of ly^ m"!- on side. 



Feb. 3. — Pupating; lesion is 2 mm. across. 

 Feb. 8. — Pupated. (Adult issued March 3.) 



(2) Feb. 17. — Has black lesion l^o mm. in diameter. 



May 26. — Same lesion now 2 mm. across; another lesion of 7 mm. Grub 

 died as result of these. 



(3) June 2.- — Two right legs with bacterial lesions. 

 June 3'0. — Three legs on opposite side now infected. 

 Aug. 14. — Grub died; discolored. 



(4) June 2. — Right middle leg infected at tij). 

 June 30. — Same leg half off. 



July 3. — Tip of left middle leg infected. 



July 7. — Tips of all legs but one infected. 



July 26. — Preparing to pupate; sickly. 



Aug. 5. — Died without pupating; infected with Mdnrihizimn. 



(5) May 3. — Has one leg with bacterial lesion. 



.Tune 7. — Pupated; pupa with tarsi of tliat leg missing. 

 .Tune 25. — Pupa died. 



(6) Feb. 5. — Has four small black lesions. 



May 26.^ — Three legs infected, ;i fourtli lialf eaten off; a lesion of 21^ mm. 



May 30. — Grub dead, discolored. 



(7) Feb. 18.^ — A lesion 1*^ mm. one one side. 

 May 26.- — Lesion is 2 mm. in diameter. 



144 



