84 



by present conditions in portions of California. Mr. Craw reports 

 in a recent letter that the San Jose scale is now exterminated in Santa 

 Clara County, Cal., where it first appeared in this country. 



PREDATORY INSECTS WHICH AFFECT THE USEFULNESS OF 

 SCALE-FEEDING COCCINELLID^. 



By C. L. Marlatt, Washington, D. C. 



When the breeding experiments out of doors were commenced with 

 the imported Asiatic ladybird (Chilocorus similis), fears were early 

 aroused for the success of the experiment on account of the abundance 

 of predaceous insects a in the small grove of pear, plum, and peach 

 trees attached to the insectary of the Department, which it was pro- 

 posed to use as a breeding- ground, inasmuch as it was thickly stocked 

 with San Jose scale. 



A great many egg clusters of the wheel bug (Prionidus cristatus) 

 and egg masses of our native praying mantis (Mantis carol i/ut) were 

 found attached to the trunks and limbs of these trees. Furthermore, 

 a large lot of the egg masses of the European praying mantis {Mantis 

 religiosa) had been shipped to us by Mr. Slingerland of Cornell, and 

 these had been placed in an open cage in the midst of this grove, so 

 that the young could escape. The hatching of these egg masses had 

 already begun. Later developments established the fact that both the 

 wheel bug and these two species of praying mantis would feed on the 

 larvae of Chilocorus and other ladybirds. In addition to this, as the sea- 

 son advanced, the larva? of the plant-lice-feeding ladybird, Adalia 

 bipunctata, were also found to eat the larvae of Chilocorus when their 

 normal food was not readily available. 



The larva? of the lace-winged fly (Chrysopa sp.) preyed more or less 

 upon the Chilocorus larva? in the breeding cages, eggs of the former 

 insect being deposited on the outside of the wires in bunches in sev- 

 eral instances, and the larva? entering in some numbers. Perhaps 

 some of the parent insects also hatched directly in the cage. A very 

 careful search of the cage had to be made for these Chrysopa larva?, 

 and a great many of them were destroyed. Comparatively few were 

 found in the grove, and at least they were not numerous enough to 

 occasion any serious alarm. 



The chief difficulty in the cage, however, arose from the presence of 

 the Adalia bi punctata. This ladybird multiplies with astonishing 

 rapidity, its eggs being laid in masses, and day after day 50 or 100 of 

 its larva? and pupa? were destroyed in this cage, and it was two or 

 three weeks before a final clearance was effected. The cage tree was 

 a fairly good-sized plum tree, and it seemed almost impossible to dis- 



« Relating to bird enemies of Chilocorus, I am assured by Messrs. Beal and Judd, 

 experts on the food of birds, that Coccinellids are rarely found in bird stomachs, 

 even in California, where such insects are very abundant. 



