July 24, 1913] 



NATURE 



53i 



most of the districts where the larch saw-fly was 

 making itself felt, and as none of the other parasitic 

 hymenoptera or diptera recovered from the cocoons 

 from year to year showed signs of attaining to 

 anything like its efficiency as a parasite, it was felt 

 that the eventual control of the pest possibly depended 

 largelv upon the future activities of this one species. 

 Hence the following observations made during the 

 present season may be of interest in so far as 

 thev indicate the probability of other of the parasites 

 attaining to a like importance. 



Shoulthwaite plantation at Thirlmere, the first in 

 that area to suffer from attack, endured during 

 several summers the severest defoliation, until in 

 1910, owing to the good offices of M. tenthredinis, 

 the ravages of the pest abruptly and almost entirely 

 ceased. In iqn it was impossible to obtain from 

 there anv further cocoons for the purposes of the 

 investigation owing to the scarcity of the saw-fly. 

 In ii)ij, however, this plantation was invaded by a 

 vast swarm of adult saw-flies, which there was reason 

 to believe came from a badly infested plantation some 

 three miles away. Owing- to a period of very un- 

 favourable weather, and perhaps to other causes, the 

 defoliation that ensued was not at all so extensive 

 as it was feared it would be ; however it was dis- 

 tinctly noticeable, and the consequences of this re- 

 infection of the area were looked forward to with some 

 anxiety. Would the trees, weakened by the old out- 

 break, have to submit to renewed defoliations, until 

 such time as M. tenthredinis, re-emerged Cincinnatus- 

 like from its obscurity, regained sufficient strength 

 to overcome the progeny of the invaders? An 

 examination of the parasites that have emerged this 

 year from cocoons collected in this area revealed a 

 quite unexpected state of affairs. Scarcely 2 per cent. 

 of the cocoons proved to be parasitised by M. ten- 

 thredinis, but some 25 per cent, yielded specimens of 

 an ichneumon which had hitherto played quite an 

 insignificant part as a parasite of the large larch 

 saw-fly (a species of Mesoleius, as yet undeter- 

 mined). From approximately 24 per cent, emerged 

 tachinids belonging to the species Zenillia pexops, 

 B. and B. (Mr. C. J. Wainwright, who kindly iden- 

 tified it for me, informs me that he knows of but one 

 other record of its having been taken in Britain.) 

 li seems highly probable that both thesi- parasites 

 have followed in the wake of the invading saw-fly, 

 particularly as observation of material from the 

 locality from which it was suspected that the latter 

 had flown has shown that the tachinid at all events 

 is exceedingly abundant there. 



It is impossible as yet to have direct proof of the 

 efficacv of these two parasites in warding off defolia- 

 tion in the areas in which thev have so opportunely 

 appeared, but it is very reasonable to suppose that, 

 here and elsewhere, they will prove to be important 

 enemies of the large larch saw-fly. 



J. M.ANGAN. 



Department of Economic Zoologv, 



the University of Manchester. 



Mackerel and Calanus. 



Referring to Prof. Herdman's interesting observa- 

 tions upon the above (Nature, July 17), I may per- 

 haps mention that the mackerel-drifters, when fishing 

 upon the usual grounds around Scillv and in the 

 Bristol Channel, are largely influenced in their selec- 

 tion of a suitable position by the finding of so-called 

 "yellow water." This condition of the sea in the 

 area under consideration arises from the presence of 

 vast shoals of Calanoids — e.g. Calanus finmarchicus, 

 Pseudocalanus elongatus, &c. — which impart a 

 yellowish tint to the surface of the water. The 

 NO. 2282, VOL. 91I 



sporadic distribution of such copepods, moreover, is 

 often somewhat remarkable ; the fishermen state that 

 it is possible at times to observe the entire extent 

 of a "splat" of "yellow water." 



The presence of mackerel is generally to be ex- 

 pected in water of this character, but heavy catches 

 are not invariably made in it. G. E. Bullen. 



The Hertfordshire Museum, St. Albans. 



THE FUTURE OF OIL FUEL. 

 "THE position of liquid fuel has increased in 

 importance far beyond any expectations its 

 most enthusiastic advocates of but little more than 

 a decade ago ever dreamed, due to the rapid 

 advances made in its use in internal combustion 

 engines. The success of engines of the Diesel 

 type, which can employ crude oil or heavier residues 

 after the lighter fractions of the crude oil have 

 been removed lor other applications, has furnished 

 the completing link in the use of oil in such 

 engines. With the petrol engine, slow-speed oil 

 engines working on ordinary burning oil (kero- 

 sene), and the Diesel and semi-Diesel engines, 

 high efficiency is now assured with any fraction 

 of the natural oil. 



The importance of liquid fuel and the certainty 

 of its more extensive use in the Navy rendered 

 it imperative that the whole question, especially 

 that of supply, should receive consideration, and 

 led to the appointment of the Committee now 

 sitting. The advantages of oil fuel for steam 

 raising were dealt with fully in these columns so 

 far back as 1902 (vol. lxvi., p. 186), when oil 

 fuel was in its early trial in the Navy. 



The present general position and future policy 

 of the Admiralty were outlined by Mr. Churchill 

 in a reassuring speech before the House of Com- 

 mons on Thursday last. Whilst the crude oil out- 

 put for last year was nearly 50,000,000 tons, 

 Naval requirements were met by fewer than 200,000 

 tons, and the Admiralty have assured themselves 

 of obtaining all requirements in time of war, so 

 long as British command of the sea is maintained. 



This necessarily involves obtaining supplies by 

 suitable contracts, and drawing specially upon 

 supplies under British control, which is now 

 possible from the Mexican fields. A far-reaching 

 step in national policy is the further proposal to 

 establish an oil refinery, so that crude oils may 

 be dealt with as they come cheaply into the 

 market. It is not only essential to have some 

 measure of control of the supply at its source ; 

 it is equally essential to provide ample storage and 

 transport facilities. The former has been arranged 

 for on a large scale in this country and throughout 

 the Empire, and by the end of 1914 the Admiralty 

 will possess thirteen transport steamers, the five 

 largest of which have a carrying capacity con- 

 siderably greater than the quantity of oil fuel 

 consumed throughout the fleet last year. 



In connection with the subject of oil fuel, three 

 Cantor lectures recently delivered by Prof. Vivian 

 B. Lewes before the Royal Society of Arts ! 

 are of especial interest. The first lecture was 



'" 1 Journal of the Royal Society of Arts, May 23, 30, and June 6, 1913. 



