82 SOME INSECTS INJURIOUS TO TRUCK CROPS. 



H. Carpenter as a cabbage pest in an article in which the larva is 

 described and illustrated in detail. As to its biology Mr. Carpenter « 

 reaches the conclusion that the female beetle laj^s her eggs on the 

 underground part of the stem and that the young larva burrows 

 through into the interior and feeds in the central tissue of the stem 

 and taproot until mature. The papal stage lasts about three weeks 

 and is passed in an earthen cell just beneath the surface. The 

 natural larval food plant is evidently a wild crucifer. 



LOCAL CONDITIONS AND NATURAL INFLUENCES. 



Inquiry was made of Mr. Eder during his visit to Washington, 

 D. C, in December, 1908, as to the local conditions in the infested 

 area. From what was learned through him it would appear that the 

 insect's occurrence in such great numbers in the hopyards of British 

 Columbia was due to the equable temperature and to the humidity, 

 which keeps the soil practically always sufficiently moist for the oper- 

 ations of the larvae feeding beneath the surface. 



There can be no doubt, from the writer's observations of our east- 

 ern flea-beetles, that these are largely held in check, especially in 

 regions like the District of Columbia, by the extremely dry heat of 

 midsummer. At the time that the flea-beetles are developing as 

 larvae or undergoing their transformation the ground is nearly baked 

 by the heat during the day and softened only by dews at night. The 

 conditions are very difterent in British Columbia, and there are, 

 moreover, no other natural causes known which might assist in de- 

 pleting the numbers of the little pest. 



Among natural agencies only a single species of insect has as yet 

 been discovered preying upon this flea-beetle, a hymenopterous para- 

 site which was known to Fitch - and which he mentions as a " Chal- 

 cidian." It is evidently a species of Perilitus, probably the same 

 species, schwarsii Ashm. ( ? ) , as has been encountered by the writer 

 on other species of flea -beetles of the genera Epitrix and Phyllotreta. 

 It develops within the body of the adult or beetle. It is not known 

 if this species occurs also in the Pacific region. If not, it might be 

 possible to introduce it. 



Fitch's observations and conclusions are interesting, since we have 

 no reason to doubt his theory, Brieflj' he observed on June 4, 1863, 

 two flea-beetles pairing on a leaf of rhubarb. Presently a parasite 

 alighted near them. It darted upon the back of the female, appear- 

 ing to be inserting its sting in the tip of her bod}^, whereupon she 

 gave a leap and they both disappeared among the foliage. Fitch 

 conjectured that the " chalcidian " was an egg-parasite of the flea- 



** Journal of Economic Biology, Vol. I, pp. 152-15G, PI. XI. London, England, 

 November, 1906. 



