View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Journal of the Entomological Society of British Columbia J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 15 Emergence of overwintered larvae of eye-spotted bud moth, Spilonota ocellana (Lepidoptera: Tortricidae) in relation to temperature and apple tree phenology at Summerland, British Columbia HEATHER L. MCBRIEN1,2 and GARY J.R. JUDD1,3 ABSTRACT We recorded daily appearance of overwintered larvae of eye-spotted bud moth (ESBM), Spilonota ocellana (Denis & Schiffermüller) in spring 1992, 1994, and 1996 in an un- sprayed apple orchard at Summerland, British Columbia, to relate larval emergence to degree-day (DD) accumulation and apple phenology. In all years the first larva was found between mid-March and early April, and none appeared after late April. Median emergence of larvae occurred when McIntosh apple trees were at early, tight-cluster stage of fruit-bud development. Larval head capsule measurements showed that ESBM usually overwinter as fifth and sixth instars, with a small proportion (≤6%) as fourth- instar larvae. In the laboratory we monitored emergence of non-diapausing overwin- tered larvae from apple branches incubated at 8.8, 9.4, 12.9, 15.0, 18.0, and 20.9 ºC. A least-squares linear regression described emergence over this temperature range rela- 2 tively accurately (r = 0.57, P < 0.05) and a base temperature for emergence (Tb = 1.0 ºC ± 0.6) was extrapolated from this regression. Regression analysis indicated median emergence should require 154.6 ± 6.7 DD above 1 ºC (DD1 ºC). Using daily air- temperature maxima and minima and 1 March to start accumulating DD1 ºC, the error between predicted and observed days to median emergence in the field was -6.7 ± 3.1 d; the regression model predicted early in every case. Using observed larval appearance on apples (1992, 1994, & 1996) and an iterative process, we determined that a combination of 6 ºC as the Tb and 1 January as a date to start accumulating DD6 ºC, minimized the coefficient of variation for the three-year mean DD6 ºC accumulations (82.7 ± 3.5 DD6 ºC) required for 50% of the larvae to appear in the field. While this latter DD index de- scribed observed emergence of larvae accurately, and its use may help improve manage- ment of ESBM, it should be validated using independent data before growers use it rou- tinely. Key Words: Spilonota ocellana, Tortricidae, larval development, phenology, degree days INTRODUCTION The eye-spotted bud moth (ESBM), hemisphere (Weires and Riedl 1991). Spilonota ocellana (Denis and Schiffer- ESBM is univoltine and larvae overwinter müller), is a pest of apple (Gilliatt 1932, in hibernaculae on branches of host plants. MacLellan 1978), blueberry (Gillespie Larvae crawl from hibernaculae in early 1985), cherry (Oatman et al. 1962), and spring to feed on leaves and blossoms. prune (Madsen and Borden 1949) through- Pupation occurs in a nest of dead leaves out fruit-growing areas in the northern and blossoms held together with silk. 1 Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, 4200 Hwy 97, Summerland, British Columbia, Canada V0H 1Z0 2 Current address: Pest Management Regulatory Agency, Sir Charles Tupper Building, 2720 Riverside Dr., Ottawa, Ontario, Canada K1A 0K9 3 Author to whom correspondence should be addressed 16 J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 Adults emerge in early summer and lay worms (Noctuidae), providing control of eggs singly on leaves (Weires and Riedl ESBM only indirectly (Madsen and Down- 1991, McBrien and Judd 1998). Summer- ing 1968, British Columbia Ministry of generation larvae arising from these eggs Agriculture, Fisheries and Food 2004). often feed on fruit surfaces causing dam- Therefore, strategies to control ESBM spe- age and discolouration beneath leaves at- cifically need to be developed. tached to fruit with silk (Gilliatt 1932). The ability to predict when overwin- In North America, ESBM has a history tered larvae of ESBM appear in spring of sporadic outbreaks in apple orchards would be a useful tool in designing an inte- (MacLellan 1978) because insecticides grated management programme. The applied in summer against codling moth, phenology of ESBM larval emergence in Cydia pomonella (L.) often control it indi- spring has been related to apple phenology rectly (Madsen and Downing 1968, British in other areas (Gilliatt 1932, Madsen and Columbia Ministry of Agriculture, Fisher- Borden 1949, Oatman et al. 1962) but this ies and Food 2004). As non-insecticidal approach has not been validated in B.C., methods like sterile male technique (Dyck Canada, and may not provide consistent and Gardiner 1992) or pheromone-based prediction of emergence on different spe- mating disruption (Judd et al. 1996, Judd cies of host plant and on different varieties and Gardiner 2004) have been imple- of fruit trees across different years. A tem- mented to control codling moth and lea- perature-based model to predict emergence frollers (Tortricidae) in British Columbia of overwintered larvae may be a more use- (B.C.), feeding damage by ESBM has in- ful approach as this technique has been creased (GJRJ unpublished data), mirror- applied successfully against other species ing reports from The Netherlands of leafrollers in the Pacific Northwest (Deventer et al. 1992). Therefore, control (Brunner 1991). We describe emergence of ESBM in spring has become more criti- of overwintered larvae of the ESBM in cal. Insecticides applied in spring are often relation to degree-day (DD) accumulations timed to control leafrollers and green fruit and apple tree phenology. MATERIALS AND METHODS Collecting and Handling Prunings. ensure they had completed diapause so that Several hundred 30-cm branch sections some portion of diapause development was were pruned from a mixed block of not included in any estimates of post- McIntosh, Delicious, and Spartan apple diapause development time. Prunings col- trees in an experimental apple orchard at lected on 2 February and 1 March 1992, the Pacific Agri-Food Research Centre when apple buds were still dormant, were (PARC) in Summerland, B.C. on 2 Febru- placed in a controlled-environment cham- ary 1992. No insecticides were applied to ber at 19 ºC under a 13:11 h L:D photo- this orchard for at least five years preced- regime provided by Daylight fluorescent ing or during this study and it was heavily tubes. On each collection date, seventy infested with ESBM larvae in 1991. Prun- 30-cm-long prunings were placed in a plas- ings consisting mainly of fruit-spur wood tic basin (35 cm × 35 cm × 16 cm), cov- and excluding previous years’ growth were ered with polyester organza and held in transported to the laboratory, stored in place with an elastic band that prevented cardboard boxes filled with moist sawdust, larva from escaping but permitted air cir- and held in darkness at 0.4 ± 0.5 ºC until culation. On 1 March, an equivalent required. length of pruned branch sections was re- Diapause Termination. Before as- moved from laboratory cold storage (0.4 sessing temperature-dependent emergence ºC) and set up identical to other pruning of overwintered larvae, it was important to samples. Every 24 h, prunings were re- J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 17 moved from their basin and tapped sharply 1 / days to emerge). Emergence rates for to dislodge active larvae onto a white all larvae at each temperature were re- cloth. The number of larvae collected gressed against temperature using least- daily was recorded and sampling was ter- squares linear regression analysis (Zar minated when larvae went undetected for 1984). Extrapolating this linear regression seven consecutive days after they began through the x-axis gave the theoretical appearing. lower developmental threshold base tem- Emergence at Constant Tempera- perature (Arnold 1959). The number of tures. On 7 May 1992, 66 days after being DDs needed for emergence of 50% of the placed at 0.4 ºC as part of the diapause larval population was determined by taking study, ca. five hundred 30-cm sections of the reciprocal of the slope of the linear prunings were removed from cold and di- regression line (Campbell et al. 1974). vided evenly among eight basins described Standard errors for estimates of Tb and DD previously. One basin of prunings was totals were calculated as described by placed in each of seven separate con- Campbell et al. (1974). Two ESBM larvae trolled-environment chambers set at 3.8, emerged within 1 d of incubation at 20.9 8.8, 9.4, 12.9, 15.0, 18.0, or 20.9 ºC, re- ºC. The emergence rates for these two spectively, each with a photoregime of larvae were considered outliers and ex- 13:11 h L:D. One basin of prunings was cluded from linear regression analysis in returned to 0.4 ºC. Constant-temperature order to maintain homogeneity of variance conditions were chosen to approximate the (Zar 1984). range of air temperatures and photoregime Phenology of Larval Emergence in normally experienced by ESBM larvae the Field. Prunings infested with overwin- during spring in the Okanagan Valley. tered ESBM larvae were collected from the When prunings were placed in controlled- experimental apple orchard in early March temperature chambers on 7 May 1992, 1992, 1994, and 1996. Collections were larvae in the field had completed emer- made while apple buds were dormant and gence. before ESBM larvae had started to crawl One larva emerged on day 54 from from overwintering hibernaculae. As be- prunings incubated at 0.4 ºC and three lar- fore, prunings mainly consisted of fruit- vae emerged on days 9, 18, and 46 from spur wood and did not include previous prunings incubated at 3.8 ºC.