December 29, 1916] 



SCIENCE 



925 



ish silk cocoon in which to pupate. Moths 

 emerge in the spring for egg-laying by the 

 time the shoots are well out. 



The Bureau of Entomology, U. S. Depart- 

 ment of Agriculture, especially requests owners 

 of peach or other fruit trees to report the pres- 

 ence of this new pest in their orchards. Speci- 

 mens of twigs may be mailed wrapped in 

 paper or, preferably, in a suitable box. 



SPECIAL ARTICLES 



THE HABIT OF LEAF-OVIPOSITION AMONG 



THE PARASITIC HYMENOPTERA 



Entomologists have for several years been 

 more or less familiar with the strange habit 

 of leaf-oviposition among the parasitic Diptera. 

 Up to the present time, however, no such star- 

 tling deviation from the normal has been ob- 

 served in parasitic Hymenoptera. 



A few years ago the writer, while engaged 

 in the study of the hymenopterous parasites of 

 the gipsy moth for the United States Bureau 

 of Entomology, carried on an investigation of 

 the life-history and habits of Perilampus 

 hyalinus, a hyperparasite of the fall webworm. 

 The first stage larva, a very curious being 

 heavily armored with chitinous plates and pro- 

 vided with numerous hooks and curved spines, 

 was found crawling about on the outside of the 

 caterpillar. Later these first-stage larvae or 

 planidia were found to bore their way into the 

 body cavity of the caterpillar, there swimming 

 about freely until the primary parasite larva, 

 either hymenopterous or dipterous, was found 

 and into which they gained entrance. The 

 Perilampus larva then remained quiescent 

 until the primary parasite became full-fed and 

 made its exit from the caterpillar to spin its 

 cocoon or form its puparium. At the time of 

 ecdysis the planidium found its way to the ex- 

 terior of the host, after which it fed as an 

 ectophagous parasite in the normal way. The 

 egg-laying habit of this strange parasite has, 

 however, remained a riddle to entomologists 

 and has been the subject of considerable specu- 

 lation. For several years the writer has been 

 looking for a solution of this problem, but the 

 opportunity did not present itself until about 

 two weeks ago. 



During the previous summer specimens of 

 Perilampus were occasionally bred from 

 Chrysopa cocoons. Recently the writer was 

 successful in capturing several adult female 

 Perilampus of this species hovering about 

 oleanders infested with Aphis nerii and fed 

 upon by Chrysopa. These were taken into the 

 laboratory and placed in vials, each with an 

 oleander leaf which bore egg-clusters of 

 Chrysopa. The insects were then watched and 

 were observed frequently to touch the tip of 

 the abdomen to the leaf. On placing the leaf 

 under the binocular microscope the minute 

 transparent eggs of the Perilampus were seen, 

 one end of the egg being slightly attached to 

 the leaf. This observation established beyond 

 doubt the habit of leaf-oviposition among the 

 parasitic Hymenoptera. The eggs are numer- 

 ous, one female depositing fifty-two in a single 

 day. They hatch in seven to ten days and the 

 first stage larva is of the planidium type. The 

 planidium is active at first, crawling rapidly 

 about, but later it attaches itself to the leaf 

 by the caudal end, standing out at right angles 

 to the surface, where it awaits the approach of 

 the Chrysopa larva and to which it attaches 

 itself by means of the numerous hooks with 

 which it is provided. 



It is difficult to understand just what is 

 gained, from the standpoint of Perilampus in- 

 festing Chrysopa, by this extraordinary habit, 

 since the Chrysopa larva is easily accessible to 

 the normal method of oviposition and is in 

 fact parasitized in the larval state by a num- 

 ber of parasites which oviposit directly into 

 the host. In the case of Perilampus hyalinus, 

 however, and other species having similar 

 habits, the advantage is obvious, since by no 

 other method could access be had to the 

 larvas of the primary parasites. In the case, 

 too, of those species of Perilampus infesting 

 wood-boring Ooleoptera and gall-making and 

 stem-infesting Lepidoptera (the correctness 

 of which records the writer is frank to confess 

 he previously looked upon with doubt), the 

 usefulness of this method of oviposition taken 

 with the active planidium stage is readily seen, 

 since in this way access is easily gained to the 

 endophagous host through the wanderings of 



