Silver, G. T.

English

Journal of the Entomological Society of British Columbia

PROC. ENTOMOL. Soc. BRIT. C OLllMIHA. VOL. 57 (1960), DEC. 1, 1960 CHEMICAL CONTROL OF LOOPERS IN STANLEY PARK, VANCOUVER' G. T. SILVER 2 Introduction Stanley Park has long been recog-nized by the Forest Insect Survey as a good collecting area for loopers, primarily the western hemlock looper, Lam b din a jiscellaria lugubrosa (Hlst.) . A heavy outbreak of this species occurred between 1911 and 1913, but by 1914 the population was greatly reduced by the action of a tachinid fly (Whitford and Craig, 1918). Many western hemlock, Tsuga heterophylla (Raf.) Sarg., were killed outright. Another outbreak caused moderate defoliation in 1929, and the Park was dusted in 1930 to prevent further damage (Hopping, 1934) . No further outbreaks of the hem-lock looper were recorded until 1958. In July, 1958, large numbers of hem-lock loopers were present, but in as-sociation with a much larger number of green-striped forest looper, Mel-anolophia imitata Wlk. By July 15 the combined population has caused light to heavy defoliation on coniferous understory trees and light defoliation to many mature overstory hemlock. Six hundred acres were sprayed by aircraft on July 26 with 10 per cent DDT to protect the trees from further damage . No appraisal was made of insect mortality but about 30 minutes after spraying the roads and paths were littered with dead and dying larvae. Samples taken on the under-story trees two days after spraying indicated a relatively large number of larvae had survived the treatment apparently protected by the thick mid-story of vine maple which exists in some sections of the heavily wooded areas. By mid-July, 1959, the number" of western hemlock looper and the 1 Contribution No. 598, Forest Biology Division, [{esear r h Branch, Department of Agriculture ot· tawa, Canada. ' 2 Forest Biology Laboratory, Victoria, B.C. green-striped forest looper were large enough on some trees that if allowed to complete their feeding it was fear-ed that top-kill could occur on some of the mature and over-mature west-ern hemlock. In contrast to 1958 the hemlock looper was the more numer-ous species. About 550 acres were sprayed between 7: 17 a.m. and 7: 43 a.m., July 25, by a Grumman Avenger aircraft from Skyway Air Services Ltd. at Langley. The insecticide was DDT in fuel oil , without emulsifier, and applied at the rate of one gallon per 3.cre. Methods Because of Park restrictions it was impossible to cut branch samples so la rval mortality was calculated by a series of prepared tests . Larvae of both species were obtained by beating trees. Small hemlock branches were tied to a lath cross-piece suspended about a foot above a 40-inch square of factory cotton stretched on a frame. Tanglefoot was placed around the edge of the frame and the ends of the cross-piece to prevent larvae from escaping. The trays for the two species were set up in pairs in a large clearing with three replications about 200 feet apart at right angles to the line of flight . Larvae were placed on the foliage on the evening of July 24, and checked again early the next morning. The trays were checked four times after spraying on July 25, and once again early on July 26. All living larvae were then taken to the laboratory and reared for 11 days on foliage collected adjacent to each tray. Spray deposit cards were set out on each tray prior to spraying, and sam-ples of the insecticide were obtained. Results The insecticide samples were an-alysed by the Chemical Control Sec-P I:0l'. ~:\ 'J"\I ' . I. SO(. B:: r' l. C( ' I.I 111<1 .1. \" (11 .. . )1 (1 ~1I.;n). DIe". 1, 10GI1 59 tion , Forest Biology Divi sion, and con-tained 7.54 per cent DDT by weight. The amount of DDT recovered from the spray depo sit cards was small, ranging from 0.0 6 to 0.10 pounds per acre . Considering th e low DDT deposits h emlock looper 18, rva l mortality was r emarkably heavy. In the three repli-c:),tions 0.06, 0.09 , and 0.10 pounds of DDT per acre wer e r ecovered, and the corre.':pol1cling larva l mortali ty three clays after spraying was 97.4,90 .4, and 96.8 pel' cent respectively. The com-bined mor tality from the three repli-cations is sh own in Table 1. Mortality TABLE I - Hcmlock looper lar val morlali1y )'csult ing from an ;]ve l'age deposit of 0.083 lb. acre DDT. St,m)r-y Park . 1959. figUl' es arc u tl ~ ,)!' r eclc(i fo r natura l m ortality . D al's afte!' No, larvae P er cen t Date 'spray j)c:lrl Livjn~ mo rtality J uly 26 July 27 ,J u 'y 28 J uly 30 July 31 August 3 August 6 1 197 19 91.2 2 199 17 92.1 :-l 204 12 94.4 5 20() 10 95 ,-1 (j 2m 9 95,8 9 209 7 96,8 12 209 7 96.8 was 91.2 per cent after 24 hours, and increased slowly to 96 .8 per cent on th e ninth day. Of th e seven survivors after 12 days four were pupae. Larva l mortalit y of the green-striped fores~ looper was] rss ~.bD.n the h emlock looper. DDT recoverey in the th ree tests was 0.06, 0.09, and 0.10 pounds per acre, and larval mortality a fter three days was '/5 .8, 90.4, and 86.5 per cen t r espectively. Mortality in the first replication increased slow-ly, but reached 86.7 per cent on the twelfth day compared with 86.5 per cent [or th~ test which received 0,09 pounds of DDT per acre. Th e data for the three re1Jlica t ions were grouped l Table 2). Total mortality bar ely reached 90 per cent , considerably less than for h emlocl<: looper. Twelve of TABLE 2-GrC'cll -, t ,'ipc r] 10l'est leop p!' la \'a I mor1ali ty r esu l ~ i Il~ f rom an avera ge de · posit of 0.083 lb . ;;r'e DDT. St2!l 1;, P :E'k, Hl5£l. F;~l:t' E' S eT C uncoL'ccl ecl [or nat ura l mortality . Dale Ju lv 26 Jul,' 27 Jul~' 28 Jul; 30 Auguot 3 August 4 August 6 1 2 l ar vae ln issing. Days after SP' a.1 ] 2 :-l ;) 9 10 12 22 lan'ae died or para <:: ites . the 27 survivors were pupae. As ma terial \vas not available to allow for check experim ents the mor-tality percentages a r e not corrected for na t ural mor tality. On .July 25, abou t 20 per cent of the h emlock looper s were in the fourth instal' and about 80 per cent in th e fifth or ul t imate in stal'. Most of th e fourth - instal' larvae died within 24 hours. The first green-striped forest looper la rvae to clrop ancl die were the sm allest. Dead la rvae the first clay No. !u rvae Dead Li\'ing 225 46 232 39 233 38 235 34' 237 32 238 31 240 27 2 P er cent mor tal il \' 83.0 . 85.ti 86.0 87 .4 88. 1 88 .5 89.9 were 23.5 per cen t fourth, 52 .5 per cent fifth, 8. ncl 2,4.0 per cent sixth or ulti -mate instal'. By the second day all fourth -instal' larvae were dead, and after the fifth day on ly last- instar larvae were a live. Based on th ese rec-ords it appears that the bes t t ime to spray for both species is no la ter than when the majority of the larvae reach the tomtl1 instal'. In this particular instance treatment on e week or 10 cl8yS earlier would have r esul ted in l1cavier mortal ity in a shorter t ime . 

Chemical control of loopers in Stanley Park, Vancouver

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Chemical control of loopers in Stanley Park, Vancouver

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Journal of the Entomological Society of British Columbia