HORTICULTURAL ENTOMOLOGY
Overwintering of Codling Moth (Lepidoptera: Tortricidae) Larvae in Apple Harvest Bins and Subsequent Moth Emergence BRADLEY S. HIGBEE,1 CARROL O. CALKINS,
AND
CHEY A. TEMPLE
Yakima Agricultural Research Laboratory, USDAÐARS, 5230 Konnowac Pass Road, Wapato, WA 98951
J. Econ. Entomol. 94(6): 1511Ð1517 (2001)
ABSTRACT Codling moths, Cydia pomonella (L.), have long been suspected of emerging from stacks of harvest bins in the spring and causing damage to nearby apple and pear orchards. With increased use of mating disruption for codling moth control, outside sources of infestation have become more of a concern for growers using pheromone based mating disruption systems. Studies were designed to provide information on bins as a source of codling moth and the pattern of codling moth emergence from stacks of bins. In these studies, codling moth larvae colonized wood harvest bins at a much higher frequency than harvest bins made of injection molded plastic (189 moths emerged from wood compared with Þve from plastic). There was no statistical difference in the number of moths infesting bins that had been Þlled with infested fruit compared with bins left empty at harvest. This suggests that codling moth enter the bins during the time that the bins are in the orchard before harvest. Emergence of laboratory reared adult codling moth from wood bins placed in stacks was found to be prolonged compared with Þeld populations. Temperature differences within the bin stacks accounted for this attenuated emergence pattern. Covering bin stacks with clear plastic accelerated codling moth development in the upper levels of the stack. Codling moth emergence patterns from plastic-covered stacks more closely coincided with male ßight in Þeld populations. This information could be important in developing a technique for neutralizing codling moth-infested bins, and in understanding how infested bins may inßuence pest management in fruit orchards that are located near bin piles. Implications for control of codling moth in conventional orchards and in those using mating disruption as the principal component of an integrated pest management system include increased numbers of treatments directed at areas affected by infested bins. KEY WORDS Cydia pomonella, codling moth, overwintering, apple, pear, pest management
CODLING MOTH, CYDIA pomonella (L.), is described by Ferro and Harwood (1973) as the oldest known and most widely distributed pest of deciduous pome fruit. The larvae feed inside the fruit, resulting in a product with little or no value. Containers or bins used to harvest pome fruits have been known to harbor diapausing codling moth larvae (Cockerell 1898, Newcomer 1936, Higbee et al. 1999). Larvae that will overwinter leave the fruit in the fall near harvest and seek out suitable overwintering sites. Once they select a location, they spin a protective cocoon that provides shelter until spring when the larvae pupate and subsequently develop to adulthood. The hibernacula normally occur under bark scales on the tree, attached to the trunk just below the surface of the ground, among the duff and debris on the orchard ßoor, or in boxes, bins and other containers used to collect the harvest (Newcomer 1933, Yothers and Carlson 1941). Although there is little published data on the occurrence or suspected effects of infested bins on codling moth populations in pome fruit orchards, there is an abundance of anecdotal observations. Early agricultural bulletins suggested that codling moth larvae 1
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infest and overwinter in harvest containers in the fall. Then the adults emerge in the spring. The impact on orchards can be signiÞcant in terms of damaged fruit if these containers are located near or transported to orchards before the adults emerge (Cockerell 1898, Cooley 1902, Sanderson 1903, Bourne and Whitcomb 1927, Selkregg and Siegler 1928, Wakeland and Haegele 1934). Newcomer (1936) found an average of 14 codling moth per apple box and was convinced that infested boxes were an important source of difÞculty in controlling codling moth in PaciÞc Northwest orchards. When anticipating the near eradication of the codling moth through areawide sterile male releases in the Similkameen Valley of British Columbia, Canada, Proverbs and Newton (1975) examined the importance of fruit containers imported into the valley as sources of reinfestation. They concluded that imported fruit boxes would provide the greatest potential for codling moth reinfestation after discontinuing sterile moth releases. Conventional organophosphatebased spray programs often are able to mitigate these effects (Cross 1985), but with the increased use of mating disruption for codling moth control (Calkins 2000) and the associated low tolerance for external codling moth populations, the issue of bins as a source
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of codling moth infestation is becoming increasingly important. Currently there are no proven commercial control tactics targeting overwintering codling moth larvae in bins. Investigations by Newcomer (1936) indicated that a steam treatment was effective and economical. He also found that treating wood props, used to support limbs, with dormant spray oil killed two-thirds of the larvae present. Lacey and Unruh (1998) demonstrated that three species of entomopathogenic nematodes were effective in controlling diapausing codling moth larvae in laboratory and simulated Þeld bioassays. Lacey and Chauvin (1999) described the use of one of these nematodes, Steinernema carpocapsae (Weiser), as a bin treatment that could be applied at the time the fruit is removed by ßotation from the bin at the packing facility. At one site of a large codling moth mating disruption implementation program (Calkins 1999), the West Parker Heights Areawide Codling Moth Management Project, we observed that pheromone traps near bin piles consistently trapped more moths than traps placed within neighboring orchards, in some cases fruit damage occurred (B.S.H., unpublished data.). Thus, studies were conducted to better understand the process of codling moth infestation of harvest bins. The objectives of these studies were to determine during what period the larvae enter the bins (before or after infested fruit is placed into the bin), to compare infestation rates of wood and plastic bins, to describe adult emergence in the spring from stacked bins, and to determine if emergence in spring by moths can be accelerated by covering bin stacks with plastic sheeting. In this report, we present the results of our studies on the dynamics of infestation and emergence from harvest bins by diapausing codling moth. This information could facilitate development of techniques for eliminating codling moths infesting bins, and enhance our understanding of how infested bins may be inßuencing pest management in pome fruit orchards. Materials and Methods Two studies were conducted to determine to what extent harvest bins are infested by codling moth larvae and the pattern of emergence by the adult moths after the bins are stacked in holding areas near orchards. Experiment 1 was designed to compare the infestation levels in plastic and standard commercial wood bins by overwintering larvae. We also compared the proportion of larvae that colonized bins Þlled with infested fruit to larvae that colonized empty bins. For this study, two orchards were selected with areas of relatively high fruit infestation by codling moth (5Ð10%). Four treatments were replicated six times in each orchard and arranged in a randomized block design within the tree rows. Each replicate consisted of two standard-sized (⬇0.7 m high by 1.2 m wide by 1.2 m deep), commercial wood bins and two plastic bins of the same approximate size (model no. 28-FV, Macroplastics, Yakima, WA). In each replicate one wooden
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and one plastic bin was Þlled with apples and other ones were empty. Wooden bins that had not been used to carry fruit for 2 yr and new, plastic bins, were placed upright in the orchards 6 wk (mid-August) before apples were harvested. After half of the bins were Þlled with fruit from adjacent trees, all bins were held for 24 h outdoors under ambient conditions (25⬚C day, 10⬚C night), then moved into a regular cold storage regime (0 Ð2⬚C) and held for 4 to 5 mo. Samples of fruit (200) from each bin were examined and the percentage of fruit infested by codling moth was calculated. After fruit was removed from the bins that contained fruit, the bins were moved from cold storage into a heated (21Ð24⬚C) greenhouse. Each bin was placed inside a large, black plastic bag Þtted with a cardboard funnel leading to a 2-liter clear plastic soda bottle. The bins were checked every 2 d and moths captured in the bottles counted and sexed. Data comparing emergence between bin types and treatments (fruit-Þlled or no fruit) were analyzed using PROC GLM two-way analysis of variance (ANOVA) (SAS Institute 1996). The objectives for experiment 2 were to characterize adult codling moth emergence from stacked wooden bins in the Þeld and to investigate whether we could accelerate and advance the period of emergence by covering bin stacks with clear plastic sheeting. Bin stacks were constructed using 216 bins (empty bins that were obtained from typical, larger stacks at storage areas near each site) in a 6 high ⫻ 6 wide ⫻ 6 deep conÞguration. Approximate outside dimensions of each stack were 7.3 m wide by 7.3 m deep by 6.4 m high. One replicate of two bin stacks was established in mid-February at each of three sites. The sites were approximately equidistant, separated by ⬇1,500 m. One bin stack at each site was covered with 6 mil clear plastic sheeting while the other stack of bins was left uncovered. Temperature probes (thermisters, Campbell ScientiÞc, Logan, UT) and 100 caged, diapausing, laboratory reared Þfth instars were placed in small cages (a plastic container approx. 15 cm long by 7 cm wide by 4 cm deep with the sides screened with organdy) at three positions (north, south, and center) in each of three levels; low (between lowest two bins), middle (between third and fourth bins) and high (between two uppermost bins). For each stack of bins this represented a total of nine probe/cage locations and 900 codling moth larvae. Moth emergence and temperature data from cages were pooled within levels for analysis. Temperature was recorded using a data logger (model CR7, Campbell ScientiÞc), and moth emergence in each cage was checked and recorded weekly while leaving the bin stacks intact. This was accomplished by gluing the end of a length of twine, sufÞcient to reach up and laterally between adjoining bins out beyond the perimeter of the stack, to the top of the cage. To remove the cage from the stack to check for emerged moths, the string was threaded through a small loop on one end of a pole, the pole was then inserted between the bins (in the space below the ßoor of one bin and the top edge of the bin below it) while pulling the twine outward until the cage was raised to the point of contact with the pole.
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HIGBEE ET AL.: OVERWINTERING CODLING MOTH AND HARVEST BINS
Table 1. Mean numbers (ⴞSE), percentage of codling moth— damaged fruit (mean ⴞ SE) and ratio of emerged males from harvest bins at each of two sites Site
Treatment
Moths/bin (⫾SE)
% codling mothÑ damaged fruit
Ratio of M:F
Campbell
Wood Plastic Full Empty Wood Plastic Full Empty
3.6 ⫾ 1.6 0.17 ⫾ 0.11 2.3 ⫾ 1.6 1.4 ⫾ 0.5 12.2 ⫾ 3.4 0.25 ⫾ 0.13 5.8 ⫾ 2.8 6.6 ⫾ 3.1
6.33 ⫾ 0.9 4.25 ⫾ 0.6 5.3 ⫾ 0.6 Ñ 4.9 ⫾ 0.7 10.3 ⫾ 1.5 7.6 ⫾ 1.0 Ñ
25:17 2:0 15:12 10:5 81:59 1:2 37:31 44:28
Wallace
The pole was then pulled out of the stack with the cage. After counting the emerged moths inside the cage, the procedure was reversed to replace the cage to the original position. To establish Þeld population dynamics, codling moth pheromone traps were placed in eight conventionally managed apple orchards within 5 miles of the study site. Field traps (model 1CP, Tre´ ce´ , Salinas, CA) were baited with 1 mg codlemone lures (CM First Watch, Scenturion, Clinton, WA) that were replaced at 2- to 3-wk intervals. Sticky trap bottoms were replaced as needed from mid-April to October and the number of male moths trapped was recorded each week. This experiment was conducted in 1996 and 1997. The effects of bin height and cover on temperature in the bin and timing of emergence by codling moth were analyzed using repeated measures ANOVA. The model has one between-subjects factor having two levels (covered versus no cover), and two repeated measures factors (bin height [low, middle, high] and year [1996 1997]). Response variables were mean Julian date of emergence, Julian date of initial emergence, and (for temperature data) Julian date that bioÞx was reached at each level in the bin stack. BioÞx was assumed to occur at 200 DD (10⬚C lower threshold) from 1 February. The height by cover interaction was invariably signiÞcant, thus we extracted simple effects contrasts (Winer 1971) comparing covered versus uncovered bins at each height separately.
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Methods for calculating simple effects contrasts and for estimating degrees of freedom following Winer (1971).
Results In the study comparing larval infestation (experiment 1), the wooden bins were infested by diapausing codling moth larvae almost exclusively relative to the plastic bins at both sites (Campbell site: F ⫽ 4.4; df ⫽ 1, 20; P ⫽ 0.049; Wallace site: F ⫽ 11.2; df ⫽ 1, 20; P ⫽ 0.003; Table 1). A total of 189 codling moths emerged from the wood bins compared with Þve from the plastic bins. The overwintering larvae excavated cavities in the wood bins to varying degrees and incorporated chewed wood from the bin into their hibernacular webbing. The larvae frequently used any irregularities that existed on exposed surfaces of wood bins. However, they also bored short tunnels (2Ð 4 cm) into the relatively smooth plywood sides of the wood bins and constructed hibernacula within the cell. There was no evidence of excavation in the plastic bins. The larvae that did colonize the plastic bins were located in relatively open spaces between structural Þns on the underside of the bins. The codling moth inhabiting the plastic bins had been preyed upon by spiders. The larvae had attached their hibernacula to the surface of the plastic, but there were no foreign substances integrated into the webbing. They appeared to be more exposed to external factors than larvae that had excavated or burrowed into the wood bins. Statistical analysis of emergence from the infested bins revealed no difference in the number codling moth emerging from bins Þlled with infested fruit compared with bins that were left empty (P ⬎ 0.25 at both sites, Table 1). Sex ratios of all emerged moths favored males at both sites (m:f ⫽ 1.59 or 58% males at Campbell and ⫽ 1.34 or 55.5% males at Wallace, Table 1). The emergence dynamics for male and female moths from both sites is depicted in Fig. 1. Males generally outnumbered females during the Þrst 30 Ð35
Fig. 1. Total number of adult codling moths emerged from harvest bins after placement in greenhouse.
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Fig. 2. Mean number of codling moths emerged from cages placed in covered and uncovered bin stacks, and mean number of males caught in pheromone traps in conventionally managed orchards in 1996.
d of emergence, while slightly more females emerged during the Þnal 14 d. The percentage of fruit damage found in the bins and the mean number of codling moth emerged per bin at each of the two sites is shown in Table 1. The levels of codling moth fruit damage at the two study sites averaged 5.3% (SEM ⫽ 0.6) at Campbell (6.3% for fruit placed in the wood bins and 4.25% for fruit placed in the plastic bins) and 7.6% (SEM ⫽ 1.0) at the Wallace (4.9 and 10.3% damage in the wood and plastic bins respectively) site. The mean number of codling moth emerged per wood bin was 3.6 (SEM ⫽ 1.6) for Campbell and 12.2 (SEM ⫽ 3.4) at the Wallace site. All larvae found inside fruit during damage evaluations had died. The most likely cause of death appeared to be asphyxiation as larval burrows and the seed cavity of the fruit were observed to be partially or fully Þlled with liquid. Emergence dynamics from bin stacks and male ßight from Þeld data collected in experiment 2 are compared in Figs. 2 and 3. Emergence of overwintering codling moth from uncovered bin piles shown in Figs. 2 and 3 was delayed relative to that from bin piles covered with plastic. There was also a delay relative to Þeld populations. The pattern of codling moth emergence from the plastic covered bin pile was similar to that of the Þeld population, both peaking in mid- to late May, but a substantial number of moths emerged in late April and early May from the plastic covered bins. Estimated Julian date that bioÞx was reached was affected by the bin level x cover interaction (F ⫽ 21.1; df ⫽ 2, 8; P ⫽ 0.0006). A plot of the means (Fig. 4) indicates that covering the bins had larger effects at the middle and high levels than at the low level. Tests on simple effects indicated that covering the bins
signiÞcantly raised the temperature in the bins (as indicated by the julian date that bioÞx was reached; Fig. 4) at all three levels compared with bins left uncovered (P ⬍ 0.01 for all three contrasts; df ⫽ 4 for all contrasts). For example, the estimated mean julian date that bioÞx was reached in 1996 was 152, 148, and 141 for the low, middle and high levels in the uncovered treatment and 120, 106, and 99 for the low, middle, and high levels of the covered treatment (Fig. 4). Mean emergence data and initial emergence data depended upon the interaction between bin level and cover (mean emergence date: F ⫽ 186.2; df ⫽ 2 ,8; P ⬍ 0.0001; initial emergence date: F ⫽ 52.8; df ⫽ 2, 8; P ⫽ 0.0002). The signiÞcant interaction was caused by the cover factor having larger effects at the upper bin levels than at the lower level (Table 2). Tests on simple effects indicated that covering the bins had no signiÞcant effects on emergence at the low level (mean emergence date: t ⫽ 2.4, df ⫽ 4, P ⬎ 0.05; initial emergence date: t ⫽ 2.6, df ⫽ 4, P ⬎ 0.05), but resulted in signiÞcantly advanced emergence dates at the two higher bin levels (P ⬍ 0.01 for all contrasts). Lastly, height effects were substantially more noticeable for the covered bins (earliest emergence at the upper level) than the uncovered bins (Table 2). The number of days during which the moths emerged was similar (about 50 d), but the moths in bin piles covered with clear plastic had a peak emergence 25Ð30 d earlier than those in the uncovered bin piles. Daily high temperatures averaged 10 Ð20⬚C warmer in plastic covered bin piles and there was a distinct gradient from lower to higher levels with increasing temperatures encountered at the higher levels. There was no signiÞcant difference (P ⬎ 0.05) in percentage emergence of moths between treatments (clear plastic cover 96 ⫽ 59%, 97 ⫽ 76%; no cover 96 ⫽ 64%, 97 ⫽ 76%).
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HIGBEE ET AL.: OVERWINTERING CODLING MOTH AND HARVEST BINS
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Fig. 3. Mean number of codling moths emerged from cages placed in covered and uncovered bin stacks, and mean number of males caught in pheromone traps in conventionally managed orchards in 1997.
Discussion Experiment 1 clearly illustrates that diapausing codling moth larvae will enter and inhabit wood bins placed in the orchard before harvest. Plastic bins were much less attractive to overwintering codling moth larvae. The results of these studies indicate that use of plastic bins for harvest would greatly mitigate bin
infestation by codling moths. Codling moth larvae have labial salivary glands that are modiÞed for the production of silk (Eaton 1988). The proximity of these web-spinning glands to the mouthparts of the larvae allows the incorporation of small bits or shavings of wood, which the insect has chewed, into the webbing of the hibernacula. This may confer struc-
Fig. 4. Codling moth degree-day accumulation and predicted Julian date of bioÞx at each of three levels of height in plastic covered and uncovered bin stacks in 1996 and 1997.
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Table 2. Average Julian date of initial and mean emergence (ⴞSE) of 2 yr for caged codling moth in plastic covered and uncovered bin stacks
Treatment Plastic Uncovered
Julian date (mean ⫾ SE)
Height in bin stack
Initial emergence
Mean emergence
Low Middle High Low Middle High
145.5 ⫾ 4.3 129.2 ⫾ 3.0 117.5 ⫾ 3.0 156.0 ⫾ 4.3 147.8 ⫾ 3.0 152.5 ⫾ 3.0
159.3 ⫾ 3.6 138.4 ⫾ 3.2 122.3 ⫾ 2.7 169.5 ⫾ 3.6 158.8 ⫾ 3.2 162.0 ⫾ 2.7
tural and protective advantages. It appears that a substrate that can be chewed is important in selecting an overwintering site. The larvae are known to have very strong mouthparts, and we suspect that they excavate the area around the chosen site and incorporate the waste into the hibernacular webbing. Bins Þlled with infested fruit and bins that were left empty had the same levels of codling moth infestation. This suggests that the majority of codling moths colonize the bins during the period that they are situated in the orchard up to the time of harvest. Although most codling moth larvae have a facultative diapause (Riedl 1983) induced by short daylength, some are univoltine even under the long photoperiod conditions that occur earlier in the season during the development of the Þrst generation larvae. Items made of wood, such as props used for supporting limbs or bins, that are near infested fruit could provide overwintering substrates for codling moths entering diapause as early as June or July. One way to minimize infestation of bins would be to place bins in the orchard as close to harvest as possible. Reported sex ratios of overwintering codling moths indicate a trend of spring emergence patterns similar to the results reported here, males dominating in the early portion of the ßight and females dominating in the later ßight period (Riedl et al. 1976, Howell 1991). However, the majority of historical data supports overall sex ratios of overwintering Þeld populations that are nearly equal or favor females (Howell 1991). Moth density is implicated as a factor in determination of sex ratios (MacLellan 1972). MofÞtt and Albano (1972) found that diapausing codling moth larvae sustained less than 5% mortality when held in a standard cold storage regime (⫺0.56 to 0.28⬚C) for 133 d. These larvae were held in ßuted cardboard hibernacula, a situation similar to diapausing larvae found in bins. Whereas, larvae that were destined for diapause, but were still in the fruit did not survive the cold storage period in the current study. Analyses of temperature and codling moth emergence data from experiment 2 indicate potential, due to decreasing temperature gradients from top to bottom levels, for prolonged and continuous codling moth emergence from large bin stacks. As indicated by degree-day accumulation, codling moths in the plastic covered treatment experienced warmer temperatures, which accelerated initial and mean emergence.
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Effects of covering the bin stacks were most prominent at the upper levels and slight or absent at the low level. Bins in the lowest level experienced the least amount of warming, resulting in the slowest development and latest emergence in those bins. This would explain the reports of sporadic border damage in conventionally managed orchards. The continuous presence of moths would allow females to lay eggs at times when organophosphate insecticide residues have aged the longest (when residues are weakest), such as just before the Þrst applications directed at the second or third generation. The implications include risk from bins arriving in an orchard from a remote location which, depending on their position within the bin stack, may contain codling moths that are near emergence. Transportation of agriculturally important insect pests by movement of the host (and vessels containing the host) is widely recognized as a primary mode by which pests colonize new areas. Transport of larvae and pupae of the oriental fruit moth, Grapholitha molesta (Busck), in bins was judged one of the primary modes (along with infested fruit and nursery stock) of dispersal of this pest in South Africa (BlomeÞeld and Geertsema 1990). The issue of codling moths being transported long distances in bins is troublesome because it may provide an avenue for pesticide resistant populations to spread to areas where codling moths are relatively susceptible to insecticides, thereby accelerating resistance development. This could negate management of organophoshate resistance in areawide programs (Siegfried et al. 1998). There is no way of predicting the presence of overwintering codling moths in any particular bin or group of bins unless the recent history of the bin(s) is known. The larvae are difÞcult, but not impossible to Þnd. Pheromone-baited traps must be placed along orchard borders to effectively identify problem bin piles in the Þeld. There are no current methods for disinfesting harvest bins economically on a commercial basis. A number of fairly simple techniques are available, such as fumigation, forcing moths to emerge into a heated storage room, or a heat treatment such as a hot water dip or steam injection which would kill the larvae/ pupae while in the bins. Segregating bins identiÞed as being from a high risk orchard and disinfesting them separately is another possible strategy. However, the cost of handling combined with the large number of bins involved renders these techniques economically unattractive to the fruit packer. Covering bins with plastic or spreading bins out rather than stacking them, are techniques that can be employed to synchronize codling moth emergence from bin piles with emergence of Þrst generation Þeld populations. A well covered bin pile would also trap moths and keep them from entering orchards. This would serve to mitigate the problems associated with a continuous stream of codling moths entering the orchard from infested bins. Unfortunately, the economics of covering bin piles with plastic sheeting may not be practical. Spreading bins in a more open conÞguration in the early spring
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HIGBEE ET AL.: OVERWINTERING CODLING MOTH AND HARVEST BINS
to encourage uniform exposure and warming would require considerably more space. One technique under evaluation is inoculation of drench tank solutions with entomopathogenic nematodes (Lacey and Chauvin 1999). Preliminary work using small-scale bins and optimum conditions look very promising. In the absence of treatments that can reliably, consistently, and economically disinfest bins, knowledge of the potential and extent of bin infestation by codling moth allows application of appropriate monitoring and control measures to solve the problem of codling moth infested bins. Acknowledgments We thank Diane Lovelace and Merilee Bayer for technical assistance. The supply of diapausing larvae by Stephanie Bloem was essential to the success of the project. We thank David Horton for assistance with statistical analysis. We are grateful to Steven Welter, Robert Van Steenwyck, and Lawrence Lacey for critical review of the manuscript.
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pests, their biology, natural enemies and control. Elsevier, Amsterdam. Lacey, L. A., and R. L. Chauvin. 1999. Entomopathogenic nematodes for control of diapausing codling moth (Lepidoptera: Tortricidae) in fruit bins. J. Econ. Entomol. 92: 104 Ð109. Lacey, L. A., and T. R. Unruh. 1998. Entomopathogenic nematodes for control of codling moth, Cydia pomonella (Lepidoptera: Tortricidae): effect of nematode species, concentration, temperature, and humidity. Biol. Control 13: 190 Ð197. MacLellan, C. R. 1972. Sex ratios in three stages of Þeld collected codling moth. Can. Entomol. 104: 1661Ð1664. Moffitt, H. R., and D. J. Albano. 1972. Effects of commercial fruit storage on stages of the codling moth. J. Econ. Entomol. 65: 770 Ð773. Newcomer, E. J. 1933. Orchard Insects of the PaciÞc Northwest and their control. U.S. Dep. Agric. Circ. 270. Newcomer, E. J. 1936. Orchard Sanitation for control of codling moth. Better Fruit 30: 5. Proverbs, M. D., and J. R. Newton. 1975. Codling moth control by sterile insect release: importation of fruit and fruit containers as a source of reinfestation. J. Entomol. Soc. B. C. 72: 6 Ð9. Riedl, H., B. A. Croft, and A. J. Howitt. 1976. Forecasting codling moth phenology based on pheromone trap catches and physiologicalÐtime models. Can. Entomol. 108: 449 Ð 460. Riedl, H. 1983. Diapause and life cycle strategies in insects. W. Junk, The Netherlands. Sanderson, E. D. 1903. The codling moth. Del. Agric. Exp. Stn. Bull. 59: 22. Siegfried, B. D., L. J. Meinke, and M. E. Schrarf. 1998. Resistance management concerns for areawide management programs. J. Agric. Entomol. 15: 359 Ð367. Selkregg, E. R., and E. H. Siegler. 1928. Life history of the codling moth in Delaware. U.S. Dep. Agric. Tech. Bull. 42: 1Ð5. SAS Institute. 1996. SAS/STAT users guide, version 6.12. SAS Institute, Cary, NC. Wakeland, C., and R. W. Haegele. 1934. Codling moth control in Idaho. Idaho Agric. Exp. Stn. Bull. 200: 3Ð9. Winer, B. J. 1971. Statistical principles in experimental design, 2nd ed. McGraw-Hill, New York. Yothers, M. A., and F. W. Carlson. 1941. Orchard observations of the emergence of codling moths from two-yearold larvae. J. Econ. Entomol. 34: 109 Ð110. Received for publication 13 September 2000; accepted 9 July 2001.
