Studies on the twigminer, &lt;i&gt;Argyresthia pseudotsuga&lt;/i&gt; Freeman, which kills new growth on twigs of Douglas-fir, showed that adults oviposited from mid-April until May on bud scales or on needles close to the buds. Eggs hatched in mid-May and larvae continued to mine in the new twigs until late fall or early winter. The insects pupated by the end of February in chambers at the bases of the twigs

Hedlin, A. F.

Ruth, D. S.

English

Journal of the Entomological Society of British Columbia

26 J . ENTOMOL. Soc. BRIT. CoLUMBIA 76 (1979) , D EC. 31, 1979 starvation because of declining numbers of woolly aphids. Biological control of the balsam woolly aphid, which is difficult to control economically by other means, could still reduce aphid popula-tions and damage if better species were dis-covered, or if releases were of larger numbers over a wider area, or if populations were pro-tected by first releasing in cages. Also, if past releases were unsuccessful simply because of bad weather or a scarcity of woolly aphid popu-lations , similar introductions could be success-ful given better conditions. One possible cause of establishment failure, low winter temperatures, should not have affected species already proven in the east, because in south coastal British Columbia and particularly on southern Vancouver Island, temperatures are milder. There may, however, have been difficulties with unfavorable weather at critical times, particularly with small delicate flies such as A. thompsoni and C. nigrocellulata. REFERENCES Chapman, J. A. and J . M. Kinghorn. 1957. Window flight traps for insects. Can. Ent. 87: 46-47. Clark, R. C., D. O. Greenbank, D. G. Bryant and J. W. E. Harris. 1971. Adelges piceae (Ratz.), bal-sam woolly aphid (Homoptera: Adelgidae): 113-127, In Biological control programmes against insects and weeds in Canada 1959-1968. Commonwealth Institute of Biological Con-trol, Trinidad, Techn. Comm. No.4. Franz, J. M. 1958. Studies on Laricobius erichsonii Rosen . (Coleoptera: Derodontidae) a predator on Chermesids. Entomophaga 3: 109-196. Harris, J . W. E. 1973. Tree and site characteristics relative to progressive balsam woolly aphid damage to Abies spp ., British Columbia 1959-1970. Pacific Forest Research Centre, Victoria, Internal Rep. BC-46. 60 pp. Harris , J. W. E ., J . C. V. Holms and A. F. Dawson. 1968. Balsam woolly aphid predator studies, British Columbia, 1959-1967. Forest Research Lab ., Victoria, Inform. Rep. BC-X-23. 18 pp. McGugan, B. M. and H. C. Coppel. 1962. Biological control of forest insects - 1910-1958: 35-216. In A review of the biological control attempts against insects and weeds in Canada . Com-monwealth Inst. of Biological Control, Trinidad, Techn . Comm. No.2. Mitchell, R. G. and K. H. Wright . 1967. Foreign predator introductions for control of the balsam woolly aphid in the Pacific Northwest. J. Econ. Ent. 60: 140-147. OBSERVATIONS ON A TWIGMINER, ARGYRESTHIA PSEUDOTSUGA FREEMAN (LEPIDOPTERA: YPONOMEUTIDAE), IN DOUGLAS-FIR SEED ORCHARDS D_ S. RUTH AND A. F. HEDLIN Environment Canada Canadian Forestry Service Pacific Forest Research Centre Victoria, B.C. V8Z 1M5 ABSTRACT Studies on the twigminer, Argyresthia pseudotsuga Freeman, which kills new growth on twigs of Douglas-fir, showed that adults oviposited from mid-April until May on bud scales or on needles close to the buds . Eggs hatched in mid-May and larvae continued to mine in the new twigs until late fall or early winter . The insects pupated by the end of February in chambers at the bases of the twigs. RESUME Les auteurs rapportent que les adultes de la Mineuse, A rgyresthia pseudotsuga Freeman, qui tue la nouvelle croissance sur les ramules de Douglas taxifolie, pondent depuis la miavril jusqu'en mai sur les ecailles des bourgeons ou sur les aiguilles pres des bourgeons eclos . Les ouefs eclosent a la mi-mai et les larves continuent de miner sur les nouveaux ramules jusque vers la fin de I'automne ou au debut de I'hiver. La pupation a lieu ala fin de fevrier dans des loges aux bases des rameaux. J. ENTOMOL. Soc. BRIT. CoLUMBIA 76 (1979), DEC. 31,1979 27 INTRODUCTION Several species of insects mine twigs and shoots of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and, when numerous, may re-duce the cone-bearing capabilities of trees in seed orchards. One of the twigminers, Argyresthia pseudotsuga, described by Freeman in 1972, has been observed for several years in seed orchards on the Saanich Peninsula of Vancouver Island. This paper presents in-formation on the biology of the insect. LIFE HISTORY AND HABITS Adult moths emerge in the spring when Douglas-fir is flowering. In 1976, caged insects emerged from April 12 to 22. In 1977, moths were observed in the field from April 25 to May 2. Periods when the various life stages occur are shown in Fig. 1. The moth lays eggs singly during April near the bases of buds (Fig. 2). Although more than 1 egg per bud may be laid , only 1 larva survives_ When the egg hatches in mid-May, the larva makes a small channel 1.5 to 2 mm long, usually just above the node and beneath an elongated bud scale (Fig. 3) . The larva moves toward the base of the twig, mining around the node, then moves toward the tip of the twig in a spiral fashion around the new wood . As feeding pro-gresses , the larva mines the centre of the twig, forming a gallery (Fig. 4) . Twenty-four galleries averaged 26 mrn in length, ranging from 17 to 35 mrn. The larva feeds until fall or early winter , moving to the base of the twig where it con-structs a pupal gallery 10 to 18 mm long, just above the node (Fig. 5). The pupal chamber is walled off from the feeding gallery by tightly packed frass and boring dust, and an exit hole is TABLE L Head capsule widths of the larval ins tars of 845 Argyresthia pseudotsuga collected during 1976 and 1977 at the Tahsis Seed Orchard, Saanichton, B .C. Sample Range Mean Std. Dev Instar size (mm) (mrn) (mrn) I 120 0.15-0.23 0.19 ± 0.03 0.02 II 131 0.23-0.28 0.26±0.02 0.01 III 165 0.28-0.37 0.32 ± 0.04 0.03 IV 232 0 .37-0.52 0.42 ± 0.04 0.03 V 197 0 .53-0.70 0.63 ± 0.06 0.04 T ABLE II. Numbers of shoots on Douglas-fir trees infested by A rgyresthia pseudotsuga, Tahsis Seed Orchard , Saanichton, B.C. (Upper four whorls only) Whorl no. Avg . no shoots Avg. no infested shoots per whorl 11 0.6 cut below the walL The larva then spins a cocoon below the exit hole. Bv November 5 and Decem-ber 6, 8% and 33% r~specti vely, of the larvae were at the base of the twig. By February 5, 72% and by March 7, 1000/0, had pupated . In 1976 and 1977, larvae were present from May 16 to Feb-ruary 5, completing their development in ap-proximately 8 months. Head capsule measurements were from reared larvae for the first two instars and from field-eollected larvae for the last three . Data in Table I provide information on larval head cap-sule sizes for the five instars . 2 104 2.2 3 153 5.5 4 260 8.2 DESCRIPTION OF LIFE ST AG ES The adult has a wingspan of 9 .5 to 10 mrn and is pearly grey, with a yellowish tinge (Freeman 1972) _ The egg is 0_34 by 0.57 mrn in size (avg of 7 eggs) , is elliptical, cream-colored, and has a reticulate surface . The young larva is about 0.6 mrn long and has a pale cream-colored body with a dark brown head capsule. The fully developed larva is 5.5 mrn long. The pupa is black and is 6 mrn long. tage S A E Jan . Feb . Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. dult - "" gg .~ Larva Pupa Fig. 1. Occurrence of stages of Argyresthia pseudotsuga, Saanichton, B .C. 28 J. ENTOMOL. Soc. BHIT. CoLUMBIA 76 (1979). DEC. 31.1979 J. ENTOMOL. &lC. B RIT. COLUMBIA 76 (1979) , D EC. 31, 1979 29 FIGURE CAPTIONS Fig. 2. Egg of Argyresthia pseudotsuga, on Douglas-fir needle. Fig. 3. Channel made by Argyresthia pseudot-suga larva above node of Douglas-fir twig. Fig. 4. Larva of Argyresthia pseudotsuga, and mined Douglas-fir twig. Fig. 5. Argyresthia pseudotsuga, pupa, exit hole and mined section of Douglas-fir twig. Fig. 6. Douglas-fir shoots infested by larvae of Argyresthia pseudotsuga_ DAMAGE Larvae kill the new shoots and reduce the number of potential cone-bearing twigs on trees. Soon after the insect begins to feed the shoot becomes flaccid (Fig. 6) and slightly lighter in color than normal foliage. By mid-July , the apica l portion ( y., to 1/ 3) of the shoot is dead and dry ; the remainder, although severely t unneled , is stil l succulent. By November, damage becomes more obvious because of the pale green foliage ; by spring, the twig has turned brown. To assess the damage caused by A. pseudot-suga, the number of attacked twigs was counted on each of the 4 whorls below the leader, on 24 trees which averaged 3.4 metres in height. The data in Table II show tha t although damage to current growth is not severe , the insect can destroy potential cone-bearing shoots. REFERENCE Freeman T. N. 1972. The coniferous feeding species of Argyresthia in Canada (Lepidoptera : Yponomeutidae). Can. Ent. 104: 687-697. 

Observations on a twigminer, Argyresthia pseudotsuga Freeman (Lepidoptera: Yponomeutidae), in Douglas-fir seed orchards

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Observations on a twigminer, Argyresthia pseudotsuga Freeman (Lepidoptera: Yponomeutidae), in Douglas-fir seed orchards

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