﻿STEAWBEERY EOOTWOEM ON GBEEFHOUSE EOSES 



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SEASONAL HISTORY 



There are two generations a year of the strawberry rootworm 

 when it sj^ends 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 

 fall — 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 

 only a few beetles are seen 

 on the plants, but they may 

 be located by searching in 

 the mulch or dried leaves. 

 In Febmar}^ many of the 

 beetles come out of their 

 hiding places and start 

 feeding. 



Very few beetles collected 

 during March have lived 

 until ]May, although a few 

 have thrived until June and 

 July. (Fig. 10.) Most 

 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, oven in .severely infested greenhouses, there are periods when 

 a r-oMi];;irativc absence of adults may lead a grower to believe that 

 .some 'iiltiiral or other melhod has successfully controlled the insect, 

 but the emergence of a new brood of adults a few days later proves 

 any decrea.se to have been merely seasonal. For example, on June 



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Fig. 10. — Time of death of 99 adults of the straw- 

 berry rootworm collected in greenhouses in 

 March, 1922. Records every Ave days from 

 March 26 to July 31 



