49 



hibernated generation, a fact which can be utilized in the control of 

 this insect in the field, since if an abundance of the wild and preferred 

 plants be available when the insects first appear it does not seem prob- 

 able that cabbage would be attacked. In short, cabbage appears to 

 be one of the last plants attacked in the field when any other palatable 

 crucifer is obtainable. The beetles not only greatly preferred hedge 

 mustard and wild pepper grass, but appeared to attack also, by prefer- 

 ence, turnip, horse-radish, and cauliflower. 



NATURAL ENEMIES. 



One would suppose from the habit of the larva of this species of 

 living within the stems of its host plant that it would not be particu- 

 larly susceptible to parasitic or predaceous enemies, and such is prob- 

 ably the case. The adult insects are so minute and inconspicuous, and 

 drop so readily from their food plants when disturbed, that they are 

 probably not often attacked, and the cocoons are very seldom invaded 

 by predaceous insects. Nevertheless the larvae are sometimes killed 

 by other insects. After a larva has made a hole in the stem, small as 

 it is, ingress is afforded to natural enemies. In a stem of horse-radish 

 growing in a spot where other larvae of this species were found at 

 Tennallytown, D. C, the pupa of a Chalcidid parasite was discovered, 

 together with a portion of the head of the larva, leaving no doubt as 

 to parasitism of the species. The adult issued June 5, and proved to 

 be Omphale livida Ashm., the same species reared from the lepidopter- 

 ous borer of Lima beans, mentioned in the discussion of that species. 

 It was originally described from Florida in 1886 (Trans. Am. Ent. 

 Soc, Vol. XIII, p. 135) under the genus Oxyomorpha. 



METHODS OF CONTROL. 



From Avhat we have learned of the life history of this species it 

 would appear that our principal reliance in its treatment lies in adopt- 

 ing preventive measures rather than in the use of insecticides. It 

 seems quite probable that injury to hothouse plants of the nature which 

 has been recorded may have been due to the introduction of soil in 

 which the beetles were hibernating. 



The utilization of 'wild food plants as a trap crop, etc. — If, as hap- 

 pened on the Department grounds the past year, the insect on its first 

 appearance finds an abundance of its wild and preferred food plant, 

 cabbage or other cruciferous crops of the vicinity are not apt to be 

 affected to any observable extent. In localities where an invasion of 

 this beetle has once occurred, it will be well to kill the insects by pulling 

 up and destroying their wild food plants — not early in the season, but 

 as soon as the adults have deposited their full quota of eggs and before 

 the larvae have left the stems. The proper time for this measure of 

 17591— No. 23 1 



