57 
THE CATTLE GRUBS OR OX WARBLES 
DURATION AND DEVELOPMENT OF THE FIFTH STAGE 
Immediately after molting, the larve are more or less translucent 
and the integument comparatively tender. The spiracles at first ap- 
pear more or less iridescent and are yellowish with a slight orange 
tinge. Growth in this stage is rapid. The integument becomes 
heavier and tougher and the spiracles darker. This darkening 
begins on the rims and gradually the entire spiracles become dark 
brown to almost black. Along with the darkening of the spiracles — 
and the rapid growth of the larve, there is a general darkening of 
the entire integument. Just prior to emergence from the host the 
grub becomes shorter and broader. Along with this change comes 
the darkening of the integument to a deep brown or black. 
The duration of the fifth stage is extremely variable. At Dallas, 
Tex., the minimum length of ‘this stage in /7. lineatum has been 
observed to be between’ 18 and 21 days. More than 100 larve were 
‘observed. In another instance there was a period of from 19 to 21 
days, but it appears that very few complete this stage in less than 23 
days. The average, based on 71 records made at Dallas, Tex., was 
30.3 days. Some of these records are given in Table 7. 
The length of the fifth stage was recorded in six larve of Z. 
lineatum at Herkimer, N. Y. The maximum was 47 days, the 
minimum 29 days, and the average 38.5 days. In 1922 in Orange 
County, N.Y, the length of the instar was determined in 19 larve. 
The een was 39, “the minimum 16, and the average 29.5 days. 
The duration of the fifth stage of Z/. Bovis was determined i in the 
case of 58 larve at Herkimer, N. Y., in 1921, and in the case of 19 
larvee at Middletown, N. Y., in 1922. The maximum, minimum, and 
average in the former were 62, 96, and 39.6 days, and in the latter 45, 
35, and 40.1 days. Some of these records are presented in Table 6. 
TABLE 6.—Duration of fifth stage of Hypoderma bovis in New York 
| | 
Mature |Dura- os 
| ae larve -| tion Larve molted to | Mature larve em- ye 
Locality to fifth emerged | of Locality fifth stage be- erged from host of fifth 
stage from fifth tween dates between dates erga 
host stage s 
1921 1921 1922 1922 
Days Days 
Herkimer____| May 13 | June 27 45 || Middletown |. Apr. 1 and 3_____- May 11 and 13____| 38 to 42 
AD QE May 18 | June 2% Boule G5 fies ee Apr. 10 and 13____| May 20 and 24____|37 to 44 
5 B Yo eS ariel (ates do____| June 18 Sileylseneere do______| Apr.19and 20____-_ June 1 and 3_____- 42 to 45 
1 DO pate IAS Ue aie) Gk 0 ees ea fs (0) ee do______| Apr. 24and 22____| June 3 and 5______ 42 to 45 
Dos fe o____| June 14 PAGy =| hes eee do______| Apr. 22 and 24____| May3land June3_| 37 to 42 
BD Oe eee feo do____| June 28 AQ We See dO sees doses es (22 June and: 35.252 38 to 42 
WMoesa 2 May 21] July 4 BAe See doses Apr. 25 and 26____| June 7 and9______ 42to 45 
Doses: May 25 | June 20 PA Sed es 2 GOs Apr. 26 and 27____| June 5and 7-__-_-_-- 39 to 42 
Does fu: May 27] July 4 Bye) Alte COE 5 a Oe June 7 and 9_____- 41 to 44 
DOs May 31! July 7 Ore Se Gone 2s Apr. Dp andioe ec ke! dG see 40 to 44 
DOs os = June 2| July 14 MD | aoe AOA S| eo ee ees Ne KOO RU ae el 40 to 44 
Dor June 4/1] July 16 42} 25 don sos | Apr. 2 and 28____| June3 and 5______ 36 to 39 
Doses June 6] Aug. 7 G2 eee (al chested as tate BG [ocala eal clears GORE Ss a ee: 36 to 39 
Dols. June July 17 easy | oem OO. 2e= Apr. 29 and May 1_| June 5 and 7_____- 35 to 39 
Doz essz June 10| July 20 40 ||_____ 022225. May Pandi2-22 2 June 7 and 9_____- 36 to 39 
DOs = = |25, dona. July: 125 Za Ne ee do____--| May 4and 5_____- June 12 and 14____|38to41 
iDgees June 27| Aug. 4 Sot ses does x4 May 5 and 6______ June 14 and 16____|39 to 42 
IDO eet June 29} Aug. 9 Alesis cae do____..| May 12 and 13____| June 19 and 21_~___| 37 to 40 
It is in chs fifth or last larval stage that stockmen usually observe 
the presence of the grubs, as the sizes of the lumps increase with the 
growth of the larvee. The sizes of the openings: through the skin 
