Ladle, Mike

Welton, Stewart

English

NERC Open Research Archive

Blandford FIyThe Rise and fdt of theBlandford Flyby Mike Ladle and Stewart Welton of IFE s River Laboratory, WarehamIn the late 1960's a problemarose when people livtng in andaround the valley of the DorsetRiver Stour were being bitten byrnsects.Intensive blological mvestigations atLhe fBA's River I door.rlory'dantiJiadthe cause of the blhng as,SimuJlumaustent now named Srmulumpostjcatum, ard established most ofthe basic ecological parameters of'rh6  cnA. ia<  Tha fami lae  ^ f  tha"Blandford Ry' , as jt rs cornmonlykrown, require a blood meal in orderlo mdtulc thetl two ro thlee hu'tdrcdeggs 'f l-e btood madls .1ye ftequentlyobtained from men and women.In May and June the inhabitants of aconsiderable area oI South Dorset areaflicted by painful bites from th-^seinsects, usually on the lower legs Thebites often bleed and are surroundedby large swellings which itch andcause considerable discorrlbfi lnsevere cases secondary n-]lectron,blistering and ulceration atlend thek-,i'es dj'd s\iTnp orns s rnh as dizzi,nessA Bt,.ndford Fly bn.The eglls ol lhe Blandford FIy taken liam Lhe nver bankand nausea have been reporled. It rsestimated that, ]r) bad years, tens ofthousands ofpeople in the towns andvillages in ard around the Stour valleyniay be blttenDespitg 5lrpnrorra ellorts in the oas..o' -' ^ --'rolr ! ! f  d  sdu oLLur . /f ^Y rha  cha^ ioe  ar r r i rn rmar t : leconomrc and poLitica.l considerationsrendered them meffective orimpractical. For example, removal ofthe laryae by the use of chemical- a c + i ^ i . i a .  r ^ r : a  ^ ^ ^ l ^ ^ , - : l ] l 'uraccept able The development ofbiologrcal control agents such asparasitic nematodes ft]ngr andviruses held lrttLe hope of a rapidfinancia ly viable solution Only theuse of cuttiag ard removaL of riverweeds and the associated modality oflarvae was believed to offer aposs biliry oI control and wds acll-a]lytried The method proved to bernefficient, dilficult and costly, wlth noprospect of long term controlHope of a new avenue ofresearch,with control poiential, arose when thepeculia-r oviposition behaviour of thespecies was discovered by our owngroup at the Institute of Fres atert r ^^ l ^mr  iThdn rho  Fraeh lM: faYB o ogrcdl Assocrdtion) l l  was already1oo,,1,'n that the "BLandford Fly' has aq i n n  o  n o n o r - " n r  c A ^ h  v a -  h  d Ieight month resting egg stage. Theegg lay[rg sites,however, remainedur discovered for ma,ry years The flyproved to be unque within theSimuliidae, in that it lays rts eggs high-and-dry in the verticaL dver banks^ h h r  i h  h l r ^ a <  u t h a r a  t h a r a  i coverhead tree cover, loamy soil withdesiccaiion cracks ar1d moist, mossyoverhangs However, there was noobvious means of destroying theeggs and although mechanicaL eggremoval was attempted and arestjmated four m hon eggs werec.ranar l  r r^-r  'ar  r ia-" t rs. t  l -  \ /6 baj i<the task of treatrrg fofiy ki]ometres ofr i r ro r  n rmrod i ^^ . i : r rn t ihdOnly with ihe commercial avaj.labilityaf Bac lus Arunngrensls did control of,9. postcalum became a realpossibility This mrcro orgarism28 NERC news J.nu,rry 199:lBlandford Flyproduces a crystalline bodY inassociation with its spore, which istoxrc to some insect larvae.Simuliidae, the family of rnsects towflch the ' Blaadford Ily'oelongs, issusceptible to one particulal strail ofthis materral knourl as Bti (Baci usthunngfie nsjs r'sraelenssJ. Thepesticide must be swaliowed bY thefly larvae and is activated by the. L,eci.{-tised cond-trons in the gxt.I'he cell walls of the gut lining rapidlybreak do\arn the larvae die.The Health and Safety Executive wasapproached a,.rd gave Nofih DorselDistrict Council permission for anexperimental appljcation of BtFollov/ing a successfu.l small scaietna] conducted by ltE h 19Bg theCor-ncil was then grven permrssronlot IFE to treat and monltor four matnriver siles of the River Stour on anexperimental basis irl 1991The requirements demanded iorapplication of 8t, assessment of' Plrn.lf^r.l trl-. ' mart:lihrenvironmental impact determLnationand the resultant reduction ]Jl bltl"lgactivity were extensive ard rigorousThe concentration of pesticide in theriver had 10 be maintahed at nogreater than 0.8 parts per million foronly ten minJles dl each applicationpoint, much less than is normally usedin Europe and other countdes forblacldly controL. This dictated thenecd  fo t  " on  l l l e  ( l i l y '  n ro i r a r l l l a ' l I l t ) n lof r ivt- ' r  l lows Siir l l  dr l l r l r( tn slt t( i tor iprovlded rnk)rf lLatron orr tr i l r [ j ] l  l l ln( lr jancl at maithLrnl i l t rcir l  n)(xjol witsappLied to esttmate tt leoretLcaL c: l I tydistances oI Bli pafiiclesPopulation densities oI living anddead Srmu/rum were determined atcontrol sites and at treated sites up toone k ometre do slream ofpestlcide applcatlon points for twelveweeks after treatment. The numbersof living and dead chironomid midgeswere determined in a similar marnerboth on weed samples and :n riverI  '  I  l r . rv " l , r  Ind ' . ^ . .  o t  nvedebra leir)f rLtrruIrlty slnlctrue were also( }j l ir i)Lis IL( )(l ,ur(l sirrnpling of drftnglninrirls ,.tnrl r-rf clLxid mtdges wzrs. . l  t , ' i , ' L r l  I n . r l l . r f n r l  f -  0 ( O  5 a r n p l o rwere laken an.l .[l.]lysed over thet w e l v a W ^ L  r '  , , l  s  | |  l y  i n  , I n  '  X ^ l . . s ewhlch invoLv(xl morc lhan il.rlf thestaff of lhe l l I: l  Rrverr [,aboratoryThe results ol lhe Lnonilonng workhave now been collatedexamhed. The overall estimate ofBlandford mortallty was 84% andhigh mofialities were observed morethan a thousand metres doMrnstreamoi the apphcation pomts . Because ofour detailed krowledge ol theblacKly ecolog-y, gained over manyyears, the river was treated when noother susceptj-ble simuliids werepresent in the larval state. There wash^ ,-lata^lihla fr^rtilitv ^finvertebrates nor was there any longia/- r'h^nrhe) chifi in .^struciure due to treatment w'1th BtlEven the chironomid midges, whichare lcro to be somewhatsusceptible to high concentrations ofBL, were not affected.Following the success ofthe I991experimental treatment the localauthorities are hoping to obtainpermrssron to treat the river as andwhen it i s appropriate.It seemsf r ob.blo lhdl lhe end is now in sightfor the notorious Blandford FIy.e bar for Btj appltcationNERC news Tanuarv I992 29

The rise and fall of the Blandford fly

http://nora.nerc.ac.uk/4578/1/N004578JA.pdf

The rise and fall of the Blandford fly

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