The Hessian Fly in California
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". ~. .: "" ~ .- - - " .... ,' ~ .-,. '-' .. :'.~'~' ;::-" - ~ '"' - "'= -, ..... ~~~ ~-~ ',' I~ 111112.~ 2 5 I~ 2 5 W 1= 11111 . 1I11~ 11111 . 1.0 3 2 w W 1 . W ~3.2 .2 II ~ ~ t.:.: Ii.£ t.:.: w w I~ I:: I:: '" ~ ... I~ 1.1 '"..;a~~ " 1.1 I..a.:.""0.::. " - 111111.25 111111.4 111111.6 111111.25 111111.4 111111.6 MICROCOPY RESOLUTION TEST CHART MICROCOPY RESOLUTION TEST \Alh~T NATIONAL BUREAU Of STANOARDS-1963-A NATIONAL BUREAU Of STANDARDS-1963-A . )"' :~);. UNiTED'ST{1TESi)E~~~~ 9F;AG~CUL~' . WASHINGTON, D. C. ' .... ~THE HESsiAN FLY I~ ·CALIFQR.NIA!), .;~4 ,." e ~ ~ 7~,' ; ~ " } uy C. M. PACJtAJili; 'Seni6r'iiintomQlogist, D£",iiWn of Om-eta and-Forage 1ft86'*s,. 1 <.;:t"" ' ,Bureau of EntOfniJpJw " ; ." . coNTENTs ' Page' PIige Ee6nomfe fmportSnce..,.. .._,..,._.; _____ '-, t Met~~!oglcal"Summer mortalitY' control~Contbiued. __________ _ History________---"-"-..:-------..:..--- 3 Artificial 16 Seasonal lilstory________________.. 4 controL____ .:_.;·________ _ -l7 Character of Injury______________ 7 Burning. stubble _______-' ____ _ 17 Development _____________________ 10 Burying stubble by plowlug ___ _ 17 Summer' cultivation 'of stubble":_ 18 " ~~: l:~k:::::=::=:::::::::::::::::::::::: J~ Spraying stubble to.kill pUI!tlrlll- 19 Early plantlng_______________ _ 20 . ~~: f~::::::::::::::::::::::::::::::::=:::: ' . ~ Rotation of crops ____________ _ 20 SummaryPlanting._____________________ resistant. varletles_____ . 20 ~~~sft~~n~~_~_~'_~:r..<>~~~::::::::::=:::::: U Literature cited _____.. _____ .:.____ _ 24 Meteorological controL____________ 15 2:; . Early spring mortality_______ 15 c ':J .' ECONOl\IIC IMPORTANCE In Californin, the H~~ian fly (PhytopMga' dest'MtCtor Say) is of economic' importance O)~Y in wheat.,growing regions near ti,.e coast, where the influence oi' :the ocean is .sufficient to prevent eXtremely high" summer temperatu~es. (Fig. 1.) Although the quantity Qf wheat grown in the valley portions of this region is being graduarly reduced year by year, the many hilly sections now devoted to wheat, will doubtless continue.so :i:rldefinitely, because they are not well If adapted for other Cl;OpS loequi,ring intensive cultivation and whiCh oi4er.wise might prove more profitable~ Wheat is one of the most dependable and suitable 01 the few crops which the hill farmers can grow~. .,'. .. .' . .... According to statistics for 1921, the last year for wh,ich figures are available by counties (1)','1. the annual value of wheat grown in the coastal counties where the fly. occurs, or is likely to occur, is in .~l1e neighborhood of $3,500,000. To this must be added the v~lJle of the wheat cut, green for h.aY',because the fly can red1,1ce h,ay yiel~ as .',' , '", , '7,2 '1-Tbo author deSire!!. to acknowledge his Indebtedness to T., D. Urbahns. Margaret. Har lhall. B. G•.Thompson, Percy .Bartiam" ,and.. C. :c. Wllson tor much valued aSlllstance ln' the counle of the work reported, In this 1!ulletin. Helpful criticism of the maliUBCript hall" been' received . from W •. B. Herms: and W. R. Wnlton. and the material assistance of d. B. Hoyt and tamilY on whose mnch many, of the <lbservations and experlmeIltl5 'Were 'cOn· ducted; Is especlai ly appreciated. .' , • Numbel"!l:.ln italic in parentheses refer to .. Literature· .cited," p. 25. ~~!~~~2~1 1 GIFT O[C 11 1929 ,. - "", -, . >"'"-""'!'I~.o7l~-" 'X~ 2~!r~mdo~ B~~~l' n. &~: OP AGRlOUL~\~.:·"1 G we,lI as grain ')'1.'• eld. IS"() sepa~at!~:~iistics are ava.ila~le for. wh\~t,~:yf: ha~r $pedh.e-"ollJy-,figu~s" gtl';ell, 'OOlJ.lg. fOl""".total.'gramscut-green ,jor. lt~at; purpos~~ Sin~ wheat. j§.-A,~he. fav:orite grain:-hay ..crop:!it ';,,', seems faIr to estimate the a¢lualv~\lue of wheat hay produced m • :"'~:"" .:" the coastal counties ~s one-h~lf of the.Jotal, or$5,&OQ,OOO. An esti-. f: r; mated tota1;>01:$9,OOO;OOO is,ther~fo~e; set as 'the value of the cyop !' :which the Hessian fly may a1feet. .. ;), ,..,. ,;',r. : .. <'1-'"'-;-."'1:1<,,1' C,AHFORI(IA 'f !. 1rAtl~.-a .•. "'~LV A8UNLJANT IDl1llI aFJ..Y PI2E5'ENT~I!l: NEY~R A"BVNtwN7 FIG. 1.-KnaWD dlstrlbuti<.ln ot .the Hessian . , • f",' " . ~ , -Just how much this insect does, reduceth~ yield is ;ery difficvJ~"~. to·'d~tmi~en.eCf.liSe of the v~riability'hiA.ts ab~dancei in di1fe1nt \ locabtIes, m- di1.l'erentfields, and even m di1ferent parts of the 138~!L field. Other factors also are' if:vQlv,~d,~ch as moisture~d other" me~orological conditions at 'critical timesiin the life histories. o~ tb:~' insect an(l its bostpl~t,together -With variations.m soil and cultural.. methods. _It is aoundant during practically every season in' ~om~: localities within its ran~e, and. where it does occur in abundance it can nf,!·t fail to cause inJury, the character and degree of which will THE HESSIAN FLY IN CALIFORNIA ::::/ bedisc.ussed later, though the injury to the total crop liable to in ~.. festation is small. All things cOllSldered, a reduction of the crop by one-half of 1fer cent seems a conservative average estimate. A reduction 0 one-half of 1 per cent on the basis of a $9,000,000 crop would amount to $45,000. A loss no greater than this is negli gible, unless some cultural method of control can be. found :which would add nothing to the expense of QTowing the crop, and which in itself might increase the yield. On the other hand, a greater loss in the wheat crop appears to result during occasional years, as indi cated by a study of the few California records published since 1879, by infol'mation obtained in talks with farmers, and by actual obser vation in the field. It th~refore is desirable that a practical method of control b!} developed which the wheat groweJ,: may have at his command, even though this be needed only occllSionally. Further !llore, when the study of the Hessian fly in Ca,.lifornia is considered as a phase of a national prohlem rather than. a.s a purely local one, it assumes greater interest and potential value. May there not be some factor, such as parasitism, which keeps the fly under control in California, and which might be utilized to advantage in the Easte:m States ~ May not a knowledge of the effects of the California climate on the life habits and distribution of the fly help to solve the problem of its control in regions where it is of greater economic importance ~ Such questions, at least, should be answered, in order to complete our knowledge and increase our ability to cope with the Hessian fly as a national entomological problem. HISTORY The Hessian fly has been present in California for many years, though, as in the ~ase of its introduction into the eastern part of the United States, the means by which it first arrived probably nev~r will be definitely known. Wheat has been grown in California \' since the first settlement, at San Diego in 1769, by the Franciscan missionaries, and it is possible that the fly may have been introduced from Spain by the original Spanish settlers, in wheat straw used fOJ.· packing. It is fairly well established that the insect was present in Spain and in the island of Minorca early in the nineteenth cen tury and had been there for many years prev,ious to that time (~, p.318). A study of the history of the Spanish occupation, however, has revealed no clues which wOl:tl<l indicate the presence of the Hes sian fly in California during that period. It m!ty not have been introduced until after the ",':lflux of Americ!tn settlers began in 1826. or even until tiie t'l'anscontinental railroad commenced operation 'in 1869. The earliest authentic date of observation seems to have been 1879. Wickson (11) mentions this date in an interesting press article on the fly. Woodworth (1~, p. 3113) reported it so abundant in 1885 I in experimental wheat plots in Berkeley "as to vitiate the culture and fertilizer experiments then under way." He also published ob servations extending from 1885 to 1889 on its abundance and on the relative susceptibility to fly injury of different varieties of Viheat under test in plots during that time. Agitation in wheat-growing and trading circles over the discovery of the Hessian fly in a field near Salinas Oity in 1899 moved Pro 4 TECHNICAL BULIJETIN 81, U.S. DE:PT:OF AGRICULTtn~FJ fessor Wickson to write the article already referred to, in which he states that the Hessian fly was definitely known to have been Ijresent in California since 1879. In those days wheat was one of tht} m'ost importaI,'lt export pr~ducts of the .State,an:danything aifectinl1' this crop affected a consIderable portIon of the populatIOn, ruraf. 'and urban; from the farmers to the crews of the clipP(lr ships which carried it abroad. Professor Wickson's brief cbrit excellent article apparently was designed to allay the fears, in the minds of mltny, that, the Hessian fiy was newly established in the region and was threatening one of the main sources of income. .. A note on the Hessian fly bt; Riley (9.) p. 131), in·the first'volume of Insect Life (1888) reads, 'For a long tinW. it was unknown ()b.' the Pacific coast, but during the fast three yilRrn it has been qui\~e injurious in parts of California.' Koebele ~U) contributed a note to Insect Life in 1890, in whi<:ih he says, ' '.rhis insect has ,beeil l'eported as being very .abundant during spring (1889') in the: central part of the State, destroying most of the wheat around Mount Eden."\ Then he continues with some interesting field and rearing notes, lDenti~ning- parasites_.