Alexander, N. E.

Allen, S. J.

Collis, D. G.

Silver, G. T.

English

Journal of the Entomological Society of British Columbia

THE GREEN-STRIPED FOREST LOOPER ON VANCOUVER ISLAND' G. T. SILVER , D . G. COLLIS , N. E. ALEXANDER , AND S . J . ALLEN 2 Introduction The green -striped forest looper. Melanolophia imitata Wlk. , was not regarded as a paten tially dangerous forest insect until it caused h eavy defoliation in 1960 on the west coast of Vancouver I sland . As this is the first record of M. imitata caus in g ser -ious damage to fo r es ted regions in Bri tish Columbia the results a re worthy of a histor ical note. The moths of this looper emer ge in April or May, mate , and each femal e lays an a verage of 80 eggs. The sex ratio is approximately 1: 1. The larvae feed from Jun e to September. West-ern hemlock, T suga heterophylla (Raf .) Sa r g., is the preferred host. Foliage of a ll ages is eaten but one-year-old needles are preferred. When feeding is completed th e larvae drop to the ground and the insects over-winter as pupae in the duff . Methods Data on annual population fluctu-ations were obtained by analysing random 3-tree beating samples col-lected on the west coast of Vancouver I sland. The extent and intensity of defoliation in 1960 was obtained by aerial s urveys. Plots and sampl e poin ts were established in localities selected to represent light, m edium, and heavy defoliation. and records were obtained on defoliation and tree mortality . The method adopted for pupa l counts, based on preliminary sampl-ing to obtain data on the di stribution of pupae, was to take four one-foot-square duff samples from beneath each tree . These were taken a lon g a straight line, two on the exposed sid e 1 ContriiJuti on ' :0 . ~OOJ Forest Entom olo g," ('IIll! Palho J og~' B r a nc h . lJ epil r ll1le nl or Forest r ." . O l· l awa ~ C;lIl ada . 2 Forest F:nloll1o \og)' a nd ]la th olng ,\ L aiJo r a tor." , \· ie-to ri a. D. C. of the tree and two on the sh a ded sid e. Sample positions were against th e base of the tree and midway be-twee n the base of th e t ree a nd the periphery of the crown . Three trees were sampled at each a rea. The a ver-age number of pupae in the 12 sa mpl es was considered representa -tive of the pupal population in eac h a rea. Results Extent and Intensity Survey record s show that in 1951 larval populations of the gr een-striped forest looper increased a long the west coast of Vancouver I sla nd. The build-up r eached its h eight in 1952 on the south side of Barkley Sound , but defoliation did not exceed 30 per cent and that only in one small a r ea. The population decreased in 1953 , an d remained at a low level until 1957. The population of the green-striped forest looper started to increase again in 1957 as shown by the occurrence of larvae in collections (Table 1) . Both occurrence and number of larvae increased in 1958, and by 1959 hi gh popula t ion s were present in the west coast drainages of Vancouver I sland , two of which are shown in Ta ble 1. The outbreak reach ed a peak in 1960 , particular ly in dra inages 005 ancl 023 . Smvey activ ities on the west coas t were seriously curtailed in 1960 du e to boat troubles, so no collections were mad e in the infes tation a rea during the larva l per iod . Heavy de -foli a ti on was reported in early Sep-tember , a nd aerial surveys la t er in September record ed defoliation r a n g-ing from light to h eavy in 32 loca liti es extending from Herbert Inlet to Naspar t i Inlet. The total a rea of visibl e feeding was calc ulated at :30 TABLE I.- Summary oj Green -strip ed Forest Loe per La rva, ) Found in Beating Samples From Drain age Divi ~ions 0 11 the "Vest Coast of Va ncouver Island . Year ';; sa mpl es including larvae Av. no. larvae ' samp le containing larva e DD 005 ' DD 023 2 DD 005 DD 023 1956 1957 1958 1959 1960 1961 o 0 20 14 47 82 88 72 85 0 61 61 , Alberni Inl et to Escalante Pt . 2 2 45 59 58 4. 14 31 7 2 Escalante P l. 1.0 sout h oJ Cape Ccoke on Brooks Peni nsu la. 22 ,755 acres, of which 4,640 had sus-ta ined heavy, 13 ,120 acres medium, and 4,995 acres light defoliation . The defolia tion limits established durin g the ae rial survey were 0-25, 25-50 , and over 50 per cent for light, med -ium, and heavy, respectively. The infested areas ranged from 30 to 6,340 acres. Visual estimates of defoliation on plot trees , and pupa l coun ts made in the same localities, a re shown in Table 2. The average number of pupae in areas of m edium and heavy defoliation was about the same. There was , however, no way of know-in g wha t 2.0 pupae per squ a re foo t meant in terms of expected la rval population or defoliation . Although ch emical control wa s no t r ecom-m ended , the need for such action was considered a possibility in 1961. Efforts were mad e in th e spring of 1961 to a ppraise the anticipated out-break . Of 75 pupae coll ec t ed and caged for adult emergence, only four produced moths, twenty were para-sitized , and the remainder died of other causes. The moth fiight at the end of May was very light, and only a small number of eggs was found in limited sampling'. At this point it was believed that the 1961 population would be too sma ll to cause appre-ciable defoliation. The predicted drop in larval numbers was confirmed by the reduced numbers obtained in beating samples (Table 1), and by the relative number of la rvae per sample collected from the same points in 1960 and 1961. Some of these were (1961 in bracke ts ) : White Pine Cove. 444 (11) ; Herbert Inlet, 262 (4) ; Beddingfi eld Bay, 460 (40); Millar Channel, 486 (120) ; a nd Tofino Inlet, 215 (28). Natural Control Parasites - The effect of parasites on th e large population of 1960 is not fu ll y known as no samples were TABLE 2.- Defolialion and Numbers of Gree n-striped Forest Looper Pupae at Sample Plot s. Septem be l' , 1960. Locaiity Ououk!ll sh Inl et Port Eliza Milb' Cha nn el Beddingfield Bay E c ls tolV Passage Vill a verde Is . Bligh I". I Defoliat ion limits de te rm in 2il Degree of defoliati on reprcsen ted ' light medium " heavy " by aeri a l s urvey. P ercentage defoliation (western hemlock ) 21 54 32 40 50 91 81 Av. no . pupae per sq. ft. of dull 0.44 0.46 202 l.92 1.46 2.06 0.50 obtained from most of th e more hea vily infes ted a r eas. Of 563 la rvae collected up to early September and reared , only 28 or fiv e per cent died of parasites. Of 133 larvae collected after mid-September, 70 per cent died of parasites, and of a total of 317 pupae collected , 104 or 32.8 per cent were paras i tized . The figure of 70 per cent la rval parasitism may be unreliable. As these collections were made late in the sea-son , many healthy larvae might have a lready dropped to the duff and pupated, leaving the retarded para-sitized larvae on the trees. The figure of 32.8 per cent pupal parasitism appears to be more reasonable, and is supported by collections made in the spring in which 26.7 per cent of the pupae died of parasites. Seven hymenopterous parasites were reared from the 1960 collections . Dusona pilosa (Walley) and Asti-phromma strenuum Holmberg were the ma jor larval parasites and were recovered only from larvae. Other species reared from la rvae were Euceros thoracicus Cresson , M eteorus sp. , and Zele sp . Aoplus cestus (Cres-son) was the most numerous pupa l parasite , followed by Gravenhorstia. alaskensis Ashmead. Three E. thor-a.cicus Cresson were also reared from pupae. It is not certain if the numbers of parasites recovered from rearin gs are related to their importance as con trol factors in the field popula tion . Disease- On May 5. 1960. while searching for pupae, small orange fru itin g bodies about % inch long were observed protruding from the duff. I n every case these grew out from a Melanolophia pupa . The fructifications were identified as the perfect state of Cordyceps militaris (Fr .) Link . The fruiting bodies were plentiful in early May but appeared only in shaded locations at the end of the month . Sampling was not inten-sive enough to determine the control exerted, but it is believed that C. militaris caused considera ble pupal mortality, and was probably one of the factors involved in the population decrease in 1961. Defoliation and Tree Mortality Defoliation estimates, made by crown levels and crown classes, show tha t feeding was, without exception , h eaviest in the upper crown levels of all classes of trees. Trees of all crown classes from suppressed to dominant were fed upon , but defoliation was heavies t in the intermediate trees. Mortality, in the plots analysed , was restricted to trees which were 90 per cent or more defoliated. Most of the remaining trees in this defoliation class were top-killed; in some in-stances the upper 2 3 of the crown was dead in 1961. Although no mor-tality occurred among' trees with less than 90 per cent total defOliation , top-kill occurred among those which were less than 50 per cent d efoliated . Aerial and ground surveys indic-ated that mortality occurred only in the stands which had been heavily defoliated in 1960. The heaviest dam-age occurred on Villaverde Island where loss was calculated at 7,300 cu . ft. per acre for the 260 acres. Average tree mortality for the remaind er of the area was calculated at 116 cu . ft per acre. Total mortality, up to the fall of 1961 , was estimated at 2,400 ,-000 cu . ft. of western hemlock . Thi s figure could be conservative as some trees which were heavily defoliated may die in the next one or two years . Discussion The rapidity with which the green-striped forest looper population in-creased to tree-killing proportions and then collapsed, allowed little time to obtain specific data on sampling techniques. With the exception of the occurrence and average number of larvae per collection no data were obtained to show correlation between population levels and defoli a tion . Al-though pupal counts were made in the fall of 1960, there was no way of determinin g if the numbers found represented a potentia lly da n gerous population. Because of the r educed population in the s pring of 1961 it was not feasible to develop a m ethod for sampling eggs. A n umber of n a tura l control fact-ors contributed to the decrease of the population . Larva l pa rasites, although no t numerou s enough to exert a ny grea t degree of control , were present in a pprecia ble numbers. Pupa l pa ra-sitism accounted fo r a bou t 30 per cent morta lity in the overwintering' popu-lation , but does not acco un t for th e hea vy pupa l mortali ty a nd the r esul t-in g low moth emergence. COl'dyceps is an unknown factor. but could h ave played a s ignificant role in the col-lapse of the ou tbreak. One of the aspects in the outbreak which is difficult at this time to explain is the severe tree mortality on Villa verd e Island. Aerial surveys, supported by ground observations, indicate that tree mortality was r ela-tive ly light on Bligh I sla nd, a lthough it is near Villaverde Island and also received h eavy defoliation. The nature of the recent infesta-tion pOints out one of th e great difficulties in dealing with looper out-breaks. The population started to increase throughout most of Vancou-ver Isla nd (in fac t throughout most r egions of the Va ncouver Forest Dis-trict) in 1958, and reached a level in 1959 whi'ch must now be r egarded a s da ngerously high . Populations r e-ma ined high or increased in 1960 only in isol a ted loca lities a long the west coast of Vancouver Island ; elsewhere the number of larvae dropped . Defoliation h eavy enough to be ob-served from the a ir occurred in 32 loca lities, tota llin g less than 23 ,000 acres, sca ttered a long 80 lineal miles of inaccessibl e coast line. Of this a rea on ly 4,640 ac res were h eavily defoli-ated , and over three -quarters of the total tr ee morta lity of 2,400,000 cu. ft. occurred on a few s mall isla nds of only 260 ac res. It' fu ture outbreaks fo llow a simila r pattern very compre-h ensive a nd d eta iled surveys would be required to detect a nd ta ke action to prevent such heavy morta lity from occurring again on other sma ll islands or inlets a lon g the coast. Summary The green-striped for es t looper which sta rted to increase in 1957 r eached severe outbreak proportions in 1960 in a large number of small separate loca lities a long the west coast of Vancouver I sla nd. The popu-lation decreased to a low level in 1961. Tree morta lity, up to the fall of 1961, was estimated a t 2,400 ,000 cu, ft. of western hemlock . This species must be added to the growing lis t of defoliators capable of causing damage to forests in British Columbia. Note on the reference collection of inflated larvae at the Forest Entomology Laboratory, Vernon, B.C. Over th f' pas t few yea r s th e refe r e nce col-lec ti on of infl a ted la rvae of lep id optero us and h ~' menoplerous t r ce defo liato rs haS bee n ex pand ed gff~a tl y . The coll ection is chi e fl y used as a refere nce a id in id e ntify in g la r Vae' take n in Survey co ll ectio ns or sub· mitted by persons in fo rest in d us try a nd r f' la ted fi e ld s . Hep rese nted in th e co ll ec tion (I r e: Fami li es Gener a Spec ies Lepidoptera 34 209 350 Hymenoptera 6 20 23 The co llection co ntain s most co mm on a nd many uncomm on defoli ators found in the for ests of inte ri o r Briti sh Columbi a . The le pidopterous fa mili es a r e r eprese nt ed by a I'a ri ed num bel' of species; for exa mple , th e co ll ectiun contains 130 species of Geometri-dae , 75 sp('cies of Noctuid ae and 15 species of Notodontid ae. The tota l number of in-na~ed iarvae is about 1.530. Thi s note is publi shed to make local ento-mol ogists [l\Var e of the ex iste nc e of th e co l-lec tion a nd to invite th em to usc it. .t. fl' . // ff/'/")/ ff/lfl iJ . . -1. 1,' ()88 . /-' I)n'sl /':/llu-II / ollJ.'I .1J L rtlif)ru/fJ/'./f. \ ' e j '/flJlI . N.f' , 

The green-striped forest looper on Vancouver Island

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The green-striped forest looper on Vancouver Island

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Journal of the Entomological Society of British Columbia