105 1olly m s made t many i food is PRELIMINARY OBSERVATIONS ON THE HABITS pterous ;he rest OF OSCINELZA FRIT, L1NN.l breed BY CUNLIFFE, M.A. (CANTAB.), ne, are NORMAN broods Christopher Welch Lecturer in Economic Zoology, ngl-, University of Oxford. tion of 3t con- (With 1 Text-figure and 2 Charts.) which of the COITCENTS. PAGE iduals Introaactory remarks .......106 leaves A. Pravalenceoftheimagointhefield ....108 pies B. Hostplantaemongwildandpturegrasses . 119 C. Appendix:- ........123 I other (1) The longevity of the imago in captivity . 123 esring (2) The value of ploughing es a repressive meeeure 125 (3) Theeffeotofmsnurialtreetment ...129 in the (4) Pal'Mi- ........132 prove summary .........la3 INTRODUCTORY REMARKS. INhis summary of our knowledge of the frit-fly, Collin(8) indicates that elucidation of the bionomics o€the fly in England is very neceaeq. 46 i Most of the data published-in recent years are Ruesian in migin, and probably not applicable to this country. [ It WSE considered advisable to ascertain the relationslip between the p 78. I fly and ite environment, therefore the following observations were made in 1919-20 with the view of obtaining evidence as to (a)the prevalence .,i of the fly in the field in the different ae.asons, and (b) the host planla I additional or alternative to cereals. Observations on prevalence in the field must be obtained in different localities, over several yeam and correlated with meteorologial con- 1 ditions, for the periods of maximum prevalence to be ked wit& the limite indud by seaeonel variations. The kation of these periods will f be of importance if control through partial immunity is eought. i' i f- 106 Observntiom on the Habits of Oscinella fiit The breeding cages used were all normal with such slight mod& tions as were required. I am indebted to the Professor of Forestry for the provision of laboratory, to Professor Somerville for permission to use apparatus 81 the part provision of an insectary, and to Mr J. E. Collin for freely placi his knowledge of the frit-fly problem at my disposal. A. THE PREVALENCE OF THE ADULT FLY IN THE FIELD DURING THE YEAR. Various authors in England have noted that the &ea swarmed certain months or on certain days-Westwood (28) in Jdy, Ormerod g on July 9th, 1888, Theobald(%) in Augustwhile Collin(8) recon that “all stages are easily obtained between May and September. Again, MacDougall(18)states that between June 21st and Sept. 29th 1 collected the fly on many occasions. A general deduction from the meage evidence available would 1 that the fly is nearly always present in the field in the warm season, bi that it becomes very much more abundant both when the oat is in er and when the grain is ripe. To test the accuracy of this view, a regular series of field observation to determine the number of flies present on the crop throughout th growing season, was made in 1919 and 1920. In conjunction with ther observations, controlled breeding experiments were conducted, to chec the field data. METHODOF PROCEDURE. By the courtesy of the Professor of Rural Economy, the observation were made on the University Farm, Sandford-on-Thames. To eliminatt as far as possible, any large influx of flies released by disturbance c other cereal crops, the field selected was one surrounded by meadowlanc the nearest cereal crop being a quarter of a mile distant. No informatio is available as to the normal extent of grass infestation nor as to th migratory powers of the adult fly. The plan (Fig. 1) indicates the relative areas and position8 of th crops grown in this field in 1919-20 and also the position (A) when sweeping operations were conducted1. Observations of the Food Production Department in June. 1919, showed that, L thia plot, 37.4 per cent. of the phta were bdyattacked, 45-6 per cent. were sttach but sending up can, while only 17 per cent. were not sttacked (is 1it.t.). NOBMANCUNLIF~ 107 modifica- The Bies appeared to frequent the ears, in largest numbers, during calm weather, hence the material was collected about 4p.m., when sion of a generally the wind has least velocity. atus and The sweepings were made with a 12ins. diameter net, similar to y placing 5LD med in ierod @I records ember.” 29th he .odd be mn, but sinear vations, out the ;h these o check Fig. 1. Field of41 =yen in which weeping raa o0uductm-lsharing mpe curiadin 1919-20. Rektive areas to eoale. Spring oata in 1919 vUiety “ Abundanoe,” in 1920 “Exoabior.” lkteeddriuinguepr&.xed. vations A. 2.5.19 Springoats. E. 1919 Roola. ninate, 10.3.20 1. ” 1920 Winterrhest. Y 20.6.20 Ryegmmsndclorer, mce of B. 28.3. 19 Spring oata. F. 1919 Rook Iwland, 10.3.20 n 1, 43.20 spring 0l.k mation C. 31.3.19 Spring oata a. 16.11.18 Winter oak to the 15.5. 19 Rye graw and clover. 1920 Rook i D. 30.10.18 Winter oak E. Llloeme.ndgnula of the 11.10.19 Winter oata where a marine towing-net, the terminal gbtnbe greatly facilitating the killing and transference of the material collected. Fifty aemi-oircular i sweep were made, as far aa possible of equal value, over the of the tope f oat phta, working up the centre of plot and keeping to the meline on each occasion. When weather conditions permitted, aollections were 1i 108 Observutions on the Habits of Oscinella frit made on alternate days. To avoid errors in idenMattion1 the frit material was separated under a binocular microscope. DATAOBTAINED BY SWEEPING. The actual figures obtained as a result of sweeping are set out in Tables I and I1 respectively, as they record the presence of the fly in the field throughout the year except for the winter period October 20th to April 27th, and it is very probable that more diligent search would shorten this period by a week or two. Table I(l919). In ‘‘Remarks” column, D=sun obscured. S =sun not obscured. Number =velocity of wind in milea per hour. No. of flies collected No. of &?a collected P Date at- A at B atC Remarks Date atA atB at c Remark July 5 144 157 112 D 11.0 Aug. 11 345 Nottaken Nottaken s 2-2 8 41 50 29 S 3.6 13 231 ,. s 73 11 308 223 161 S 7-3 15 686 ,, S 6.6 13 78 10 34 D 13-2 17 502 ,. D 8.8 15 145 105 77 s 10.2 20 1437 ,, s 7.3 17 1110 364 135 S 4.4 22 22 ,, ,. D 13.9 21 168 98 Nottaken D 8.1 24 541 ,, 9. s 51 23 160 67 , D 14-7 26 56 ,, 9. a 23-5 25 453 361 D 4.4 28 Nil ,, ,. D 16.9 27 461 483 155 D 0-7 31 23 ,, 19 S 8-8 29 472 468 Not taken D 2-9 Sept. 1 Cmpcut 31 127 93 ,, D 10-3 Aug. 2 43 17 ,, D 9-5 5 216 268 114 S 8.1 From gnrss headlands, pm 7 306 Nottaken Nottaken S 5-1 cadwe as for oats 9 161 ,, ., S 5-9 Oct. 7 16 1913 411 After Oct. 19th. no captures in field. Sweepings on B and C were discontinued after August 5th m the @urea obtained up to thst date were confirmatory to those shown under A. The abundance of the flies on July 17th and An@ 20th. after reiny periods, should be noted. Mr J. E. Collin has informed me (in I&.) that he ia convincad O.+ ie the only Speciee attacking oats in England. Only occasionally waa 0. pwsilka Meig. observed in the material collected (which in- cluded approximately 12,000 specimens of the frit-fly) and then never in large numhem nor wa~this speck ever redfrom puperis collected from oats in the field. On the other hand 0. puaiUa wm bred from barley grains, collected at Garsington, Oxon.. the flies emerging on 17.8.20. Mr Collin, in confirming the identi6cation, stated that, ma far PB he wm aware, this is the 6ret word of thie species attaaking aedm Eughd. Again, this species WBB bred from field specimens of Hordeurn rnwinutn, two Bies emerging on 13.10.20. NORMANCUNLIFFE 109 Table I1 (1920). In “Bemprks” colnmn, D =sun obeoared. S=mm not obecnred. NumLmr=veloaity of wind in milea per hour. No. of fiea No. of fliee Date collectedatA Remsrka Data collectedatd Red April 28 1 162 June 18 32 D 8-8 30 Nil 11.0 21 168 6 9-6 %Y 2 11 16.2 23 375 s 8-1 4 5 11-0 26 222 D 7-3 6 1 17-6 28 206 D 11.0 8 19 11-7 30 298 S 11-7 9 48 S 4.4 July 2 76 D 14-7 10 66 S 6-6 34 Toowetformeaping 11 26 D 8-8 9 38 S 13-9 13 37 8 13-2 12 88 D 14-7 16 12 D 11.0 14 so . D102 19 42 D 11-0 16 293 D 11.0 22 79 S 8-8 19 469 D 12-4 24 18 8 8-8 22 18 D 16-9 27 28 D 8.1 24 38 8 102 29 21 D 14-7 28 62 8 9.6 31 7 D 11.0 27 31 8 13-2 29 102 8 4-4 June 2 76 8 9-6 31 12s B 8-8 4 42 D11-7 dog.