609 



A Pteromalid, Elachistus nigritulus, Zett., which is probably a parasite 

 of L. slrobilclla, is on the wing from mid-May to early June. The 

 author's reason for beheving it to be a parasite of the moth and not 

 of a gall-midge is that its larvae appeared on one day in large numbers, 

 and a Lepidopterous larva can harbour many Pteromalid parasites, 

 whereas a Cecidomyiid larva obviously cannot do so. 



RuscHKA (F.). Zwei neue Chalicidier aus Fichtenzapfen. [Two new 

 Chalcids from Spruce Cones.] — Zeitschr. aiigew. Ent., Berlin, 

 viii, no. 1, September 1921, pp. 160-161. 



This is a description of the new Chalcids, Eufelus piceae and E. 

 stvobicola, mentioned in the preceding paper as probable parasites of 

 Pcrrisia strobi, Winn. 



BoRXER (C). Zur Heimatfrage der Reblaus. [On the Question of 

 the Original Habitat of the Vine Louse.] — Zeitschr. angew. Enf., 

 Berlin, viii, no. 1, September 1921, pp. 163-167. 



Lindinger's view that the original habitat of the vine louse {^Phyl- 

 loxera vastatrix] is the shores of the Black Sea [R.A.E.,- A, ix, 256] 

 is considered untenable, and the reasons why it must have come from 

 America are given. 



North America is the home of the majority of Phylloxerids, and 

 nearly all species producing specific leaf-galls occur there exclusively. 

 The vine-louse was discovered on an American vine by Asa Fitch 

 in 1854, and later on it was found on wild vines in the Mississippi basin. 

 European outbreaks did not occur before the sixties, and it is almost 

 certain that they followed the importation of infested material from 

 North America. All attempts to practise viticulture in North America 

 with ungrafted European vines have failed, since no variety of the 

 European vines, Vitis vinifera and V. silvestris, is immune to this 

 pest. In its original habitat both susceptible and immune vines 

 must have been present, and the wild vines in America at the present 

 day show all gradations from complete susceptibility to complete 

 immunity. The fact that some vines of eastern Asia are very resistant 

 and even partly immune shows that the resistant and immune American 

 vines are not the result of selection against the Aphid, but that the 

 latter has gradually adapted itself to certain varieties. In connection 

 with this view it may be found that two or more biological races of 

 the vine louse occur in America. Recent breeding experiments under- 

 taken by the author with the object of transforming root forms into 

 leaf forms indicate the probability that the original habitat of the 

 genus is the primeval forest harbouring the tropical or subtropical 

 genus, Vitis, on which this Aphid was able to live, not only in leaf- 

 galls, but on all parts of the plant, both above and below ground. 

 The author considers that this was possible in the uniformly moist 

 rain-forests of the tropics or subtropics. The root forms in his 

 experiments infested (and produced galls on) the leaves and shoots 

 irrespective of daylight, provided a uniform optimum degree of 

 moisture was supplied. According to this view the root form is an 

 earth-inhabitant because it finds there the necessary moisture. The 

 present-day tj^pe of root form was first fixed when the Aphid spread 

 to drier regions. The leaf-gall-producing forms have, on the other 

 hand, retained their original biological characters, as their closed galls 

 protect them against climatic changes. 



(4873) 2 § 



