DISPERSAL BY FLIGHT OF LEAFHOPPERS (AUCHENORRHYNCHA: HOMOPTERA) BY N. WALOFF Departmentof Zoology and AppliedEntomology, ImperialCollege, London S. W.7. INTRODUCTION In thelast fewyears a seriesof studieson thebionomics and ecologyof leafhoppers have been carriedout at theImperial College Field Station,Silwood Park,Berkshire. Results of a surveyof the speciesbreeding in acidic grasslandshave been reported(Waloff & Solomon 1973). Dispersal by flightof leafhoppersand the catchesin the aerial suction traps and in variousinterference traps, have also been studied.The interestin these problemsis two-fold,firstly, because dispersalto and frombreeding sites contributes to fluctuationsin the sizes of populations(see May 1971; Tay 1972; Solomon 1973) and, secondly,because many of these plant-suckinginsects are vectorsof plant diseases; transmittingviruses or mycoplasmato variousgraminaceous crops, clover, strawberries and otherplants (Slykhuis& Watson 1958; Watson & Sinha 1959; Raatikainen & Tinnila 1959; Maramorosch,Shikata & Granados 1968; Fewkes 1969; Nakasuji & Kiritani1970). Littleis knownabout thetimes of the year in whichthe leaf hoppers in Britaindisperse by flight,and theseaspects have been summarizedin thispaper. In thiscountry, leaf- hoppersare consideredpests of minorimportance only, but in partsof Europe,in North Americaand in tropicalcountries the effectsof transmittedplant diseases and of direct damage caused by leafhopperson cropsassume a highsignificance. Recently, the direct effectsof feeding,coupled withthe intenseoutbreaks of the delphacidSaccharosydne saccharivora(Westw.) on sugar cane throughoutthe Caribbean have been described (Metcalfe1971). Closely associatedwith dispersal by flightare the problemsof alary polymorphism, whichare both widespreadand diversifiedthroughout the Auchenorrhyncha. METHODS Flight Dispersal by flightwas investigatedby recordingthe numbersof Auchenorrhyncha capturedin the aerial suctiontraps (Johnson 1950, 1957; Johnson& Taylor 1955; Taylor 1951, 1955, 1962). Traps IL and IV are permanentlysited east of Elm Ridge at Silwood,adjacent to one another,with trap II suspended1 2 m and trapIV 9*1m above groundlevel. Both are 46 cm in diameterand the inputof air is 71 m3/min.A third suctiontrap, 12 2 m above groundlevel and 65 m westof the other two, has beenoperated since 1969.It is referredto as the Rothamstedtrap (R.T.). Supplementarysuction-traps, 23 cm diameter,were also used in thisstudy. They were locatedon sitesof populationstudies on Psanimotettixconfines (Solomon 1973),Cicadella viridis(Tay 1972) and Stenocranusnminutus (May 1971). Anothersimilar trap which 705 706 Dispersalby flight of leafhoppers >~~~ . ). O, 10t ... .......... ^ 0) Cd,0 . *n............... ., . Q . ~o < 0)I 0 . .. X ,D -4.-~.Cd . .. F -) Cmd . _so~~~ . ON ON en***c o r. ts < 0 . ..). ~~~~ . Cd . .. o~~~~~~~ ~ * ^- ~ o~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-4 (n *?* - ?*??*?Q * o~~~~~~~~~~~~~ X~~~~t-) M)* ~ - ) * . ) ) ) ~* ~ ~~~~4 0 t~~s_ Ce * ee *Q U- 6 ....... ~~~~~~~~+I - O ~~~~~~~- 4C. s ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 46 s ia) s~~~~~~Z O. 3 qj* @,-, A4 I .}g4a ,a N. WALOFF 707 . * . ... ....4 . ... ....I . .***** ***N* * ** . cn . *. c o * * * * * O * ~~~. 00N. ^*o..N . * * q * * . cn0^ *n .4t ,* r--( cn 00~~~~~~~~orCl * 00 . o** . 'r-s . a . 0 . N 00N %,o N ON _I ***eD*ss *- *0 *efnO. * _ CZ C cl Z~C ~~~~.. * E Z +... - CZ a cd~~~~~~~~~. * . cn L = cl 4.o- Ln l . *** **. ** . .. .... .. .. .. .. .. ** . * . n . .-. ** . *** ........ .00~~~~~~~c. ... ... .. .. .. .. .. .. .. .. .. .. .. -. +. CZlC .~~~~~~~~~~~~~~~~~~~~~-.- O, - A-AE = = r4 $- cd A A w CZ9 Z - _ - U _ * , - _ -~~~~~ ~~ ~ ~ ~ -~~~~~~~0~~Z ~3 Q* 3':E Z t: 0)~~~~~~~~~~~~~~~~~z-t3 E, ~, z , , S C Z o' ~ P, $ C4,W Q to1 R wWi b tia s iS * b~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'or~ Q~ 0 0 Q cmcd~~~~~ Z t~~~ - ~~~~~t Z~~-v - Q -x E~ 2b > ( ~~4' c4Q) ~ -4 44 44 44 C4 (,J-~~~J, 4 LL1 708 Dispersalby flight of leafhoppers O D . ?*.**. _I.*.** . *. **. .* . *. *.t. a o o a) ~~~~~~~~~~~m kn .. >,D st * * * * * _I _I **. * **. *.*. * . I.*. *. *. *. *. *. * . kn <~~~~~~~~.t . 0k * ** ***-' *_Ien. ._ . .. >,D ~ ~~~~~~~~~~~.t- .- t * * * * * *_ . Cd Cd ~~~~~~~~~~~~0~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 0 CZ *. I * It . _I _I . _I . _I . d .D . N. Cd N . N . .... ................................. - . $. 1. C) z Ut~~~~~~~~~~~~~~~9 > o = $. C: 0C Cd tz I Q 0 CZ O e > Q t ? 34! A > > u 2 2 r CZ Ew Hem~~~g;4N44wN~~u~~sCZ= -u zz N. WALOFF 709 'IC . .. .. .. .. s . *. ? *00 * n - * _- ^ *m _I**t*t * N * n . *. .b** r 00en-N *n mo en * * * ** ^.* . * . * t * N -. N* * _ I m . ... _ *. *00l * . .. * . en . ... .. * . * . c .XNO . *St . *_ . .. cnE E U Ed ? E 'o?< cd0 r j LL~t~a~aRU~dUR~~~~~~~~~~~ s = ts 0 h%c Co) :~~~~-< ~~~~~~~o d 9 , Q 2 z g ' ' ' " "2 ki~~~E 0 U +I =$ Co 710 Dispersalby flight of leafhoppers segregatedthe catch into hourlysamples was erectedby traps II and IV in 1972. In addition,water traps and pots containinggrasses on whichthe flyinginsects landed weresuspended at 0l6, 1 2, 1 8 m above theground level within the area of study(Waloff & Solomon 1973).There were two watertraps and tensets of suspendedpots distributed throughthe 1-hafield. The catcheswere removed daily and preservedin 7000 alcohol forsorting and identi- ficationin winter.The data weresupplemented by catchesmade in 1962.Simultaneously, withsampling of the aerial populations,the seasonal abundanceof the acidic grassland species was recordedin the fieldand the methodsused are summarizedin Waloff& Solomon (1973). Flitting Flittingwas examinedin 1968,when ten sets,each of threepots withgrasses, which were periodicallyrenewed, were suspendedon poles at heightsof 0-6, 1 2 and 1-8 m above the groundlevel. The thirtypots wereexamined daily and any leafhoppersthat settledon themwere beaten on to a tray,collected and recorded.It can be seenin Table 2, thatas generationtime progressed, fewer insects settled on thehigher pots and more on the lowerones and thiscoincided with greater proportions of matureindividuals. Females were dissectedand the immatureones given the value of - 1, those with developingoocytes -2, and thosewith fully developed eggs -3 and spentfemales -4. The indicesof maturitybeing the averages of thesevalues. It maybe inferredfrom these data (Table 2) thatmature individuals tend to flit. Laboratorytests Some laboratorytests were made to see whetherthe leafhopperswould continueto flyon reachingmaturation. These werenot testsfor migratory abilities but theyhelped to distinguishbetween the femaleswhich retained flight ability throughout their lives fromthese that lost it withage. The insectswere gently shaken out of a tubeat a heightof 0l6 m intoa container1Il0 m longwith muslin sides and roof,a transparentwindow at one end and an open side at the releasingend. Some flewstraight to thewindow, others dropped on thefloor and hopped towardsit. This was repeatedfive times with each individualinsect. Secondly, the insects werereleased on to thefloor, one at a time,and gentlyprodded with a paintbrush, some onlyhopped, while the flyershopped and flitted.This was also repeatedfive times with each insect.The flyersand non-flyerswere then dissectedto ascertaintheir state of maturationand measurementsof their body length, the length of thefore and hindwings and of hindtibia (Table 7). Macrostelessexnotatus, Balclutha punctata retained powers offlight to death,whereas in otherspecies, e.g. Arthaldeus pascuellus, Streptanus sordidus, Euscelisplebejus, Diplocolenus abdorninalis, Elymana sulphurella, the older femaleswith abdomens distendedwith eggs, appeared to lose the abilityto flyand only hopped. RESULTS The seasonal incidenceof flying Auchenorrhyncha The seasonal incidenceof flightof leafhoppersand froghoppersis summarizedin Table 1. One hundredand fifteenspecies were identifiedin the catchesin the Silwood traps; threeCercopidae, fifty-eight Cicadellidae, twenty-nine plus Typhlocybinae,two Cixiidae and twenty-threeDelphacidae. This list constitutesone-third of the British speciesof Auchenorrhyncha. N. WALOFF 711 Table 2. Numbersof leafhopperssettling on grass in pots suspendedat differentheights and the indicesof maturityof thefemales in thesamples (1968) Date No. in Heightabove ground sample 1-8m 1-2m 0-6m 1-8m 1-2m 0-6m Proportionof sample Indexof maturity 16-31 May 17 0-88 0-12 000 1-3 - - 1-15June 42 0-67 0-21 0-12 1-7 1-5 16-30June 45 0-22 0-51 0-27 1.9 2-5 - 1-16July 36 0-14 0-28 0-58 1-8 2-0 2-7 The yearlycatches were small, the combined totals from traps II, IV and R.T. ranging betweena 1000and 1400in 1969to 1972.Generally, about one-halfof each annualcatch comprisedJavesella pellucida,Macrosteles sexnotatusand M. laevis only (Table 3). All are activeflyers, but not the most abundantlocal speciesand are vectorsof plant diseases.Javesella pellucida transmits the Europeanwheat striate mosaic virus(Watson & Sinha 1959) and the Macrostelesspp. carrythe 'astersyellow' mycoplasma. The proportionsin whichthe different families of Auchenorrhyncha formed the monthly catches in aerial traps are given in Table 4. As most delphacid species hibernateas nymphs,their adults were the firstto emergeand formedthe bulk of the catchin April and May. By June,the Cicadellidae,most of whichhibernated as eggs,were the most abundantboth in thefield and in theair, while the numbers of adultdelphacids declined. By mid-July,the second generationof adult delphacidsemerged and theirincidence in the aerial trapsrose. The second generationsof cicadellidadults tended to overlapwith thedelphacids, but whereasthe latter