5.66 



NA TURE 



[Oct. 13, 1887 



At the meeting of the International Meteorological Com- 

 mittee at Paris in 1885, Dr. H. Wild, of St. Petersburg, and 

 Prof. E. Mascart, of Paris, were requested to take the initiative 

 in the publication of a series of international meteorological 

 tables, to allow of a uniform method of reduction of the obser- 

 vations being everywhere carried out, and a specimen has now 

 been printed and issued for criticisms. The work contains (i) a 

 •description of the tables and of their use, in English, French, 

 and German ; (2) equivalents of various units, and general 

 tables used by different' countries for meteorology, magnetism 

 and electricity. The volume will occupy nearly 440 pages 

 quarto, and will cost about 30^'. The Committee request each 

 country to contribute to the expense of publication by subscribing 

 for a certain number of copies. 



We have received the results of meteorological observations 

 made in New South Wales during 1885, under the direction of 

 H. C. Russell, B.A., F. R. S., the Government Astronomer, 

 forming a compact octavo volume of 360 pages, with plates of 

 meteorological curves for each month. The great increase in the 

 number of rainfall and river stations has made it necessary to 

 publish these observations in a separate volume. Some important 

 additions have been n^.ade to the information given in past years, 

 and the barometric curves have been so arranged as to show the 

 various changes through all the stations atone view. The tables 

 show (i) the most important data for the whole colony ; (2) the 

 data for each station separately ; (3) the barometric curves ; and 

 {4) the monthly abstracts pu'lished during the year. Consider- 

 able attention has been paid to the amount of evaporation in 

 various parts of the colony, and the quantities for some districts 

 are found to be much below what has often been stated, depending 

 very much upon the state of the soil. The year 1885 was 

 one of serious drought, although the total rainfall for the year 

 was only 10 per cent, below the average, owing to heavy rain- 

 storms at the end of January. The total rainfall at Sydney was 

 3978 inches measured on 145 days. The greatest fall was in 

 June, and the least in August. The mean temperature for the 

 year was 63° 9. The maxiii.um in the shade was 97° '6 on 

 November 5, and the minimuin 40° '6 on June 30. The mean 

 temperature of the whole colony for 1885 was 63^"o, or \°-'] in 

 excess of the mean for 15 years. The absence of cloud, and the 

 drought, have had a decided effect upon the temperature of the 

 whole colony, showing apparently a direct relation between 

 rainfall and temperature. 



THE PROBLEM OF THE HOP PLANT LOUSE 

 (PHORODON HUMULI, Schkank) IN EUROPE 

 AND AMERICA} 



"T" HE author has been for several years carrying on investiga- 

 tions with a view of ascertaining the full annual life-history 

 of Phorodon Iiumidi, and especially with a view of settling the 

 hitherto moot question as to its winter life. The importance 

 of the inquiry, both from the economic and the scientific sides, 

 is self-evident. The hop crop, in all parts of Europe where it is 

 grown, and especially in England, annually suffers more or less 

 from the ravages of this its worst insect enemy, and in some 

 years is a total failure. The same is true in North America, at 

 least eai-t of the Rocky Mountains, and last year the injuries of 

 this Phorcdon in the hop-growing regions of the State of New 

 York were so great that many hop yards were abandoned and 

 have since been ploughed up ; while but 10 per cent, of an 

 average crop was harvested. From the purely scientific side, 

 entomologists, notwithstanding the great interest attaching to 

 the subject, have been divided in opinion as to the identity, or 

 specific relationship, of the hop Phorodon and one that occurs 

 on Prunus, while the complete annual cycle of the insect's life 

 has remained a mystery. After full and satisfactory investiga- 

 tions I have satisfied myself that, contrary to the prevailing im- 

 pression among hop growers and previous investigators, the hop 

 plant louse does not hibernate underground on the roots of the 

 hop, nor in, on, or about anything in the hop yard ; but that, 

 upon the advent of the first severe frosts, the hop plant and the 

 hop yards are entirely cleared of the species in any form. I find 

 that all statements to the contrary in America are based on mis- 

 apprehension, or mistaken identity of species, and I believe 



• Ab>tract of a Paper read before Section D of the British Association for 

 the Advancement of ^Science, at Manchester, by Prof. C. V. Riley, on 

 September 3. 



(though admitting the possibility of variation in this respect in 

 milder cliiriates) that the same will be found to hold true in 

 England, where hibernation on the hop root has been accepted 

 by high authority. The positive statements made about eggs 

 being laid in autumn, whether on roots or upon the vines left in 

 cutting, or which are carted away, are based on conjecture, and 

 have been blindly copied without credit by one writer from 

 another, a practice too common among second-hand writers on 

 economic entomology. 



The conjectures of some of the best students of aphidology 

 W\2ii Phorodon liunitili had a form {vialaheb, Fonsc.) living on 

 Prunus, and that there was a consequent migration from one 

 plant to the other, I have positively proved to be correct, by 

 direct colonizing from Prunus to Humulus, and by continuous 

 rearing from the original stem-mother hatched from the winter 

 egg- 



The observations have been made on growing plants and in 

 vivaria at Washington, and checked by others made simul- 

 taneously in hop yards at Richfield Springs, N.Y. An incident 

 may here be recorded as illustrating the effect of meteorological 

 extremes upon Aphides. The extreme heat (over 100° F.) and 

 dryness of July 17 and 18 killed every one of the insects under 

 observation at Washington, entirely clearing the plants. The 

 economic bearing of such exceptional phenomena, as also of the 

 biological observations made, is readily understood. 



The more important conclusions from the studies so far made 

 are thus summed up in a paper which I had the honour to read 

 before the American Association at its recent meeting in New 

 York :— 



(i) Phorodon hzvnuli \\\\>trn7ite% in the winter egg state, this 

 egg being fastened to the twigs (generally the previous year's 

 growth) of different varieties and species of Prunus, both wild 

 and cultivated. The egg is difficult to detect, because it is 

 covered with particles which resemble the bark in colour and 

 appearance. It is usually laid singly, and when freed of dis- 

 guising particles is seen to be ovoid and O'O; mm. long. 



(2) The annual life-cycle is begun upon Prunus by the sterti- 

 mother, which hatches from this winter egg. The stem-mother 

 is stouter than the individuals of any of the other generations, 

 with the legs, antennae, and honey-tubes relatively shorter, while 

 the cornicles between the antennae are sub-obsolete. The 

 colour is uniform pale green, with bright red eyes and faintly 

 dusky tarsi. 



(3) Three parthenogenetic generations are produced upon 

 Prunus, the second at once distinguished by its more elongate 

 form, much longer members, distinct cornicles and markings of 

 d-irker green ; while the third (or typical malah-eh form) becomes 

 winged, and instinctively abandons the plum and migrates to 

 Humulus. The habit of moving from plant to plant after giving 

 birth to an individual, and thus scattering the germs of infection 

 on Humulus, is well marked in this winged generation. 



(4) During the development of the three plum-feeding genera- 

 tions, the hop is always free, and subsequently, until the return 

 migration, the plum becomes more or less fully free from infection 

 by this species. 



(5) A number of parthenogenetic wingless generations are 

 produced on the hop (seven, or the tenth from the stem-mother 

 on plum, having been traced up to August 5, and advices of the 

 eleventh, up to August 19, have been received since my arrival 

 in England) ; and, finally, there is a return migration of winged 

 females to the plum in autumn. The wingless hop generations 

 are not only incapable of migrating to the plum, but do not thrive 

 upon it when artificially transferred thereto. 



(6) Exact observations are not yet complete as to the full 

 number of generations produced upon the hop before the winged 

 return migrant appears, and another month's careful watching 

 and experiment is needed to fill this hiatus in the annual cycle, 

 as also to ascertain the exact nuaiber of generations produced in 

 autumn on the plum. From knowledge extant and previous 

 general observation, the facts will probably prove to be as 

 follows : — ~ 



(7) The eleventh or twelfth generation will produce winf 

 females (from the middle to the end of August), which will deposit 

 their young upon the plum, and these will become the onlysexedj 

 individuals of the year, the male winged and the female wingless, 

 the latter after coition consigning a few impregnated or winter! 

 eggs to the twigs. _ \ 



(8) Up to August 5 the fir.-t females on hop were still alive 

 and breeding, having existed two months. There is, conse- 

 quently, an increasing admixture of generations from the first. 



