THE CLOVER ROOT BORER 23 
TABLE 5.—Results of experiments on incubation of eggs of the clover root borer, con- 
ducted at Forest Grove, Oreg., in 1916, 1918, and 1919 
Date of - | Number | 
Sieeencapat Mean | Time of laeftectival Accumt- 
Number of eggs penne Pate wt _tempera-| incuba- | of days | | tempera- lated tem- 
aan g | pure |: tion 45° F. | ture | perature 
1916 1916 OBS NE TOES Peas fle focdte 
Doe 23 Oe a ee aetna Miry(3--\ssune 628. 53.8 | 35 32 $371 281.6 
A 2s coi Ee eg oe epee ola Ne SEL Sh PaGenr es gee 53.9 33 30 | 8.9 | 267.0 
[ io De eens wa oe ec 12e= 102 54.5 30 30 9.5 | 285. 0 
1725 |e ere eos ee ae 7s 1D ees: 54.8 31 31 9.8 303. 8 
[ 2] per sie So ae See 1922 13(2) ?__ 55.6 26 26 | 10.6 | 275.6 
[iid baa epee see Se rans 19__) be ieee 56. 1 27 PHY =| idle aka 299. 7 
pers se ee so oe ESS Ps) 14(4)___| 57.4 21 21 12.4 | 260. 4 
“DENSI 2 See a ae er sea 29_ 15(4) - =x 59.2 18 18 14.2 |} 255. 6 
TES r ec ome eee a aes cate oe | June 20- July so) oes 59.3 19 19 | 14.3 | Qi lear 
9) Nc 2s SB ee eo eee ee ee Rp Pe Ra J aes BEA oe Say Ase deere 60. 7 18 18 LST 282. 6 
2) 2 oe ean nee 26-2 | a cae Soe 60. 9 16 16 | 15.9 | 254.4 
lege na Pie eee te se SS PASSE is eee 61.0 19 19 | 16.0 | 304. 0 
ber] ae SS en ae | Dee TQ bss ee 61.9 18 | 18 16.9 304. 2 
Fi (Sl Le ee RS SS eee Saas 225} i hoje Be 62.3 17 17 | VES 294.1 
7:5) sa a ae eae a Re | 9__| 24(2) --- 62.3 16 16 | ies 276.8 
eel OiSuee| 1918 | 
Ware ounted == eo = May 21-| June 10-2 59. 4 21 | 21 | 14. 4 302. 4 
| 1919 1919 
1D Yo Stents Bas ac eee ee June 3 __| June 24____-_ 58.8 | PAE 2 22 |} 13.8 303. 6 
db ojec es eters VE Ree eS er ge aj aon Qh saee 58.9 23 | 23 13.9 319.7 
‘1 Bracketed items in the first column refer to the same lot of eggs. 
2 Figuresin parentheses in third column indicate the number of eggs found hatched on the date 
named. 
It appears irom these records that the incubation period in the 
Pacific Northwest is very much longer than Schmitt (39, p.394) noted 
for Germany, or than Parker recorded for Hagerstown. The records 
also show that this period is longest in May and considerably shorter 
in June. As incubation occurred in what may be assumed to have 
been an atmosphere of uniformly high humidity, temperature is prob- 
ably the determining factor causing the difference in incubation period. 
It is possible that there are sufficient differences in the mean daily 
temperatures at this season in different localities to account for some 
of the recorded differences in the incubation period. 
The incubation period of about 3) days in April and May as deter- 
mined by laboratory methods is shown by field observations to be 
approximately correct for the Willamette Valley, and seems more 
nearly to correspond with the seasonal history as recorded in the field 
at other places. It is concluded from experimental evidence that the 
incubation period in clover roots at effective temperatures varies 
from 32 days in May and early in June to 16 days in June in western 
Oregon, and, judging provisionally from observations made else- 
where, is perhaps as short as 10 days in some localities where soil 
temperatures average considerably higher. 
LARV4 AND LARVAL MINES 
Newly hatched clover root borer larvee were found to be helpless, 
inactive creatures incapable of locomotion on a smooth surface. The 
leverage made possible by the small egg cell, with its opening into 
the egg gallery securely plugged, seemed a absolutely necessary for the 
successful attack of the larve on the clover roots. The young larva 
