Venables, E. P.

English

Journal of the Entomological Society of British Columbia

16 B. C. ENTOMOLOGICAL SOCIETY Aphelinus mali Hald A Parasite of the Woolly Aphis E. P. VENABLES, ENTOMOLOGICAL LABORATORY, VERNON, B. C. The control ot 1l1juri()us insects by parasites is a subject which is receiving- a gTeat deal o f attention at the present time in all parts of t he world. This spec ial phase of insec t control is now, as a rule, in the hands of specialists 'who devote th emselves to the study of the subject in a ll its aspects . In various parts uf the w orld parasite laboratories have been established, which serve as centres of clistribution of the desired species uver wide areas . In Canada, the Dominion Entomolog-ical Bra nch has a pa rasite laboratorv at Bell evi lle, Ontario, where a staff is maintained for supplying- parasites for all parts of the Dominion. The promiscuous intruduction of parasites into various districts is re ceived with Ii ttle favour. The dange r of introdu cing, with desired species, secunda ry, o r hyper-parasites , is one of the reasons for exercis-in g- particular Gu-e in this ·wo rk. Such an introduction would possibly result in the destructi on of the para site itself. The best method of shipping the insects, whether in the adult, larval or egg stage, much be studiecl carefully, and be the subject of experi-ment before any extensive shipments are made. In our work dealing with th e control of the w ooll y apple aphis, Eriosoma lanigera :thus. in the interior of British Co lumbia the natural enemies of the insect have been studied. Among the large numbe r of preda tors attacking the insect Syrphid fEes are probably the m ost im-portant; their influence reaching its maximum of efficiency late in the season. In certain sections of the United States, and in Eastern Canada, the aerial form of woolly aphis is attacked by a minute Chalcid fly known as Aphelinus mali Bald. This insect confines itself t o destroying those aphids on the upper portions of the trees and has little influence upon the forms attacking the roots . The absence of the root form of the woolly aphis in the Okanag-an Valley, tog-ether with the absence of the parasite Aphelinus mali Bald, was a matter of interest. The serious in-festat ions by the aerial form of the woolly aphis in the district coupled with the connection of the insect and the Perennial canker disease of apple trees, sug-g-ested the advisability of introducing the insect. The successful introduction of Aphelinus mali into many parts of the world has been carried out with excellent results. The parasite has become established in Eng-land, France, Japan, New Zealand, Australia, and U rug-ua y, to mention only a few of those countries, into which the insect has been artificially introduced. PROCEEDINGS, 1931 17 Regarding both New Zea la nd a nd Aus trali a it is from these coun-tries that the most optimisti c accounts have appea red dea ling with the contr()1 'of the wooll y aphis by the Aphelin us . In New Zeala nd the para-site was wide ly spread during 1922 and 1923, becoming well establi shed at a ll points of liberati on. Its effect upon the woo ll y ap hi s was such that those in touch with the fa ct su rrounding th e infestations were of the opinion that the para site wou ld , under normal conditions, so reduce the num be r of the aph is that the necessity of spraying would be tremen-clous ly red ucecl . I n :.Jew Suuth \Na les the Aphe linu s has done exce ll ent work. Dr. Till ya rd w ho "vas responsible for the in troduct ion of Aphelinus mali Hald. in to Aust ra lia shows th at the resu lts have been quite spectacular. ] t is of inte rest to note that Aphelinus mali Hald. exis ted in :.Jew South \Na lcs prior to its in troduction from Kew Zea land , a nd was bred from the Chrysanthem um aphi s, as recorded by 1\ 1 r. \N. B. Gurn ey in t he Agri cultura l Cazette of New So uth Wa les, 1926. The stoc k brought from New Zea la nd , ho wever, attacked the vvoo ll y aphis a nd is th o ruughl y establi shed. Tn France the parasite is esta bli shed but t he natu ra l predators of th e woolly aphis so reduced the in sects th at the stock of Aphelinu s became somew hat dep le ted each seaso n, a lthoug h being well establi shd . Regarding th e work cl one with Aphelinu s in th e Oka nagan, the parasite was imported in 1929 from Ontario. Mr. A . B. Ba ird, in cha rge o f the Domini on Parasite Labo rato r v a t Bell ev ille, unde rtook the rea r -ing of the parasites, wh ich were shi pped tu Ve rnon as they be ca me ava il ab le. The fi r st shipm ent was se nt off on A ug ust 28th a nd ar rived in Ve rnon on Septembe r 3rd. N ine shipm ents we re received, and a tota l of 508 living parasites were li be ra ted du ring Septembe r . These insects were a ll sent in the ad ult stage. Va rious me thods we re tested in making these shipme nts. A consider-ab le numbe r we re se nt in sm a ll via ls, enclosed in the rm os Aask s. In some cases the via ls we re enclosed in flas ks enclos ing wate r , th e via ls being cor ked a nd the co rks waxed. Ot he rs were enclosed in sma ll icc boxes w ith th e via ls in rack s. A few shipments were sent bv illr mail. The mos t success ful method, a nd th e one resu lting in the lovvest mo rta li ty , co nsis ted of via ls w rapped in cutton a nd packed in w ooden boxes with no other pro tection. The parasites sent by this latter methocl ar rived in excell ent condition. Tn most cases each vial was provided with ha lf a ra isin w hi ch was pinned to the cork. Th is supplied moisture a nd food fo r the pa ras ites , whi ch were obse rved to feecl upon the cut surface o f th e fruit . The parasites, as received, ",:e re li berated o n woolly aph is infes t ed trees in th e Ve rnon dist ri ct. P racti ca ll y a ll th e in sec ts were placed on 2-single tre e at Coldstream, which carried a verv heavy infestat ion. In 18 B. C. E N TOMOLOGICAL SOCI ETY libe rating th e Aphelinu s th e co rk s we re remo ved from th e via ls a nd the latter vve re stood up in a box in th e t ree and th e pa ras ite s a ll owed t() m a ke th eir w ay ou t. Se ve ra l cases of ovipos iti on \ve re no ted as soon a s th e paras ites reac hed a colony of aphid s. A t th e prese nt tim e, we a re unable to say w ha t the result s o f the impo rta tio n of Aphelinus mali m a y be in the 'future . C nde r Oka naga n conditions th e woo ll y aphi s passes the winte r a t th e base of tl-ees, on th e wa te r sprou ts, a t g round leve l, a nd a lso upon the trunk s a nd m a in limbs in kno t ho les, and va rious pro t ec t ed sit ua -t ions cau sed by m ec ha ni ca l injuries to th e ba r k; pruning wound s and sun scald ca nke r s a re favll ri te sites in whi ch t he in sects may winter success -full y. Th e m() rtali ty a mong t he aphid s is heavy duri ng cold wea th er, a nd only a sma ll pe rce ntage of t he a u t u m n in festat ion sur vives. The dest ru ct ion wroug ht by th e w inte r, co mbined w ith th e a t tack of Sy rphid larvae in spring may, a t t im es redu ce the numbe rs o f aphi ds to such a n exte nt as to red uce the cha nces of the Aphelinu s from fi nd ing a suffi cie ncy of woo lJ y aphi ds in w hic h to la y th e ir eggs. I n Fra nce t he nu mbe r s of Aphe linu s a re at t im es se ri uusly de pl eted by the a ttacks uf aphi d preda to rs a nd ot he r ca uses. A t Ve rn on vve a re cage ing in th e tree in 'whi ch th e Aph elinu s we re li be ra ted ; thi s tree w ilJ be a rtifi cia ll y infested w ith a phids thi s spring in o rde r to secure a plent iful supply u f mate ri a l fu r the paras ite t o wo r k upo n. Thi s tree w ilJ be u sed as a centre of d is tri bution fo r th e parasite during th e next few sea sons, 

Aphelinus mali Hald A Parasite of the Woolly Aphis

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Aphelinus mali Hald A Parasite of the Woolly Aphis

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Journal of the Entomological Society of British Columbia