STRAWBERRY ROOTWORM ON GREENHOUSE ROSES 29 
SEASONAL HISTORY 
There are two generations a year of the strawberry rootworm 
when it spends its life in greenhouses. The curious feature of its 
habits under greenhouse conditions is the pseudohibernation which 
| it undergoes. The beetles which emerge in late summer and early 
falli— August, September, and October—pass the greater part of the 
winter in hiding, either in the surface mulch or in the dried leaves 
on the plants. During this time they are not in a true dormant 
state, since they occasionally come from their hiding places, par- 
ticularly on warm, clear days, and feed. It is possible that this 
habit can be accounted for as a vestige of the natural life of the 
insect out of doors, where it hibernates as an adult in a true dormant 
condition. 
Since a minimum temperature of 60° F. at night and about 80° F. 
during the day is maintained in rose houses during the winter, tem- 
perature conditions apparently do not account for the semidormant 
state of the beetles. From 
November until February °° [I 
only a few beetles are seen 26 }-#HY +- +14 4 
on the plants, but they may 3%, IEICE 
be located by searching in © 20 7 
the mulch or dried leaves. 36 a ae | 
im February many of the < “Ci ia : ial 
beetles come out of their 2 io} }ti -| eek 
hiding places and start #8 $0 an LL ene 
feeding. zoe N | No 
Very few beetles collected patil lk SEN mS 
during March have lived esi 8 10 15 202530 $10 15 2025 508 10 15 202829 810 15 202530 © 
until May, although a few Fic. 10.—Time of death of 99 adults of the straw- 
have thrived until June and berry rootworm collected in greenhouses in 
: March, 1922. Records every five days from 
July. (Fig. 10.) Most Maren’ 2¢ to suly 31 
adults collected in May and 
June have lived through the summer and fall months, and a few 
individuals have survived until December. Reference to Table 5 
will show a general decrease in the number of collected adults during 
two general periods, April and May, and August and September. _ 
Egg laying commences early in March, continuing through April 
and to a limited extent in May. From these eggs develops a new 
brood of adults which emerge from early May until late in July. 
The maximum number of beetles are found from late in June until 
August, which is also the period of severest injury to the plants. 
Many individuals of the second brood, which develops from eggs 
deposited by these beetles, and which emerges during September and 
October, live through the winter and lay eggs the following spring. 
The generations are usually indistinctly separated, owing to the 
long period of egg deposition and the fact that a female may continue 
laying eggs after adults have developed from her earlier eggs. Fre- 
quently, even in severely infested greenhouses, there are periods when 
a comparative absence of adults may lead a grower to believe that 
some cultural or other method has successfully controlled the insect, 
but the emergence of a new brood of adults a few days later proves 
any decrease to have been merely seasonal. For example, on June 
