Spotted cutworm, Xestia c-nigrum (L.) (Lepidoptera: Noctuidae) responses to sex pheromone and blacklight

J. Appl. Entomol. ORIGINAL CONTRIBUTION Spotted cutworm, Xestia c-nigrum (L.) (Lepidoptera: Noctuidae) responses to sex pheromone and blacklight P. J. Landolt 1, C. Guédot 1 & R. S. Zack 2 1 USDA, ARS, Yakima Agricultural Research Laboratory, Wapato, WA, USA 2 Department of Entomology, Washington State University, Pullman, WA, USA Keywords lures, monitoring, pheromone, spotted cutworm, trapping Correspondence Peter J. Landolt (corresponding author), USDA, ARS, Yakima Agricultural Research Laboratory, 523 Konnowac Pass Road, Wapato, WA 98951, USA. E-mail: peter.landolt@ars.usda.gov Received: April 29, 21; accepted: June 28, 21. doi: 1.1111/j.1439-418.21.1571.x Abstract Traps baited with the sex pheromone blend of (Z7)- and (Z5)-tetradecenyl acetate captured significant numbers of male spotted cutworm moths, Xestia c-nigrum (L.) compared to unbaited traps. Nearly no males were captured in traps baited with (Z7)-tetradecenyl acetate, the major pheromone component. Antennae of spotted cutworm males responded to (Z7)-, (E7)-, (Z5)- and (E5)-tetradecenyl acetate in the laboratory; however there was no response by moths in the field to the E isomers when presented in traps as major and minor components respectively of a binary blend or to the (E7) isomer as a single component. These findings clarify the makeup of a sex attractant that can be used for monitoring X. c-nigrum on agricultural crops in Washington. However, multiyear season-long monitoring of spotted cutworm moths in Yakima Valley apple orchards revealed differential responses to pheromone and blacklight traps. A spring flight period showed a strong moth response to the pheromone compared to blacklight, while a later summer flight period showed a weak moth response to the pheromone relative to blacklight. At this time, we do not know which trap type might best indicate spotted cutworm abundance and risk to crops. Introduction The spotted cutworm, Xestia c-nigrum (L.), is highly polyphagous (Tietz 1972) and is a widespread pest of numerous crops in temperate regions of North America, Asia and Europe. It is noteworthy for its early spring damage to leaf and flower buds. The spotted cutworm is a significant pest of several crops in the Yakima Valley of eastern Washington state and causes occasional economic damage to vineyards, orchards and various row crops (Howell 1979). There is interest by growers in monitoring spotted cutworm moths for determining the need to look for larval damage to crops and for the purpose of timing pesticide applications. Howell (1979) used blacklight traps to define the seasonal pattern of spotted cutworm moth activity in the Yakima Valley of Washington. However, such traps are generally not used for agricultural pest monitoring because of purchase and maintenance costs and difficulties in sorting non-target insects that are captured. Moth sex pheromones are much more selective as attractants and can be relatively inexpensive and long lasting. A sex attractant pheromone can be used for trapping adult males of the spotted cutworm, but there may be taxonomic or geographic variance in the chemistry of the female sex pheromone and in the response of males to female pheromonal compounds. Roelofs and Comeau (197) trapped Xestia (Amathes) c-nigrum (L.), probably in the state of New York, with both the Z- and E- isomers of (7)-tetradecenyl acetate [(7)-14Ac], presented singly. They reported that a larger form of the moth was trapped with (Z7)-14Ac, while a smaller form of the moth was trapped with (E7)-tetradecenyl acetate [(E7)-14Ac]. J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA. 593

Spotted cutworm responses to sex pheromone and blacklight P. J. Landolt, C. Guédot and R. S. Zack The smaller form of the moth may have been X. c-nigrum (=Amathes adela Franclemont), while the larger form may have been Xestia dolosa (=Amathes dolosa Franclemont) (Hudson 1981). Hirai (1976) subsequently isolated the Z isomer of (7)-14Ac from females of X. (Amathes) c-nigrum in Japan and reported captures of males in traps baited with (Z7)- 14Ac. Ando et al. (1977) in Japan also captured a small number of X. c-nigrum in traps baited with (Z7)-14Ac. Steck et al. (1982) in Saskatchewan, Canada, captured increased numbers of males of X. c-nigrum in traps baited with the combination of (Z5)-tetradecenyl acetate [(Z5)-14Ac] and (Z7)-14Ac, compared to (Z7)-14Ac alone, and captured relatively few moths in traps baited with (Z7)-14Ac alone. Mayer and McLaughlin (1991) suggested that the moth may vary in its pheromone communication with geography. Subchev et al. (1996) showed that (Z5)-14Ac inhibited male spotted cutworm response to (Z7)-14Ac in Europe. This contradiction in prior reports indicates a need to verify responses of local spotted cutworm moths to these compounds. We sought to obtain a clearer understanding of the response of local X. c-nigrum to sex pheromone, in order to recommend a sex attractant for use in monitoring this species in agricultural crops in central and eastern Washington. We tested prior reports, treated here as hypotheses, that a local spotted cutworm is: (i) attracted to (Z7)-14Ac; (ii) is more strongly attracted to the blend of (Z7)-14Ac and (Z5)-14Ac; and (iii) is attracted to the corresponding E isomers of the same compounds. We used the sex pheromone to determine the seasonality of sex attraction and to verify the seasonal phenology reported by Howell (1979) using blacklight traps. Materials and Methods Evaluation of pheromone compounds. Field experiments were conducted to evaluate the attractiveness of possible sex pheromones of the spotted cutworm. All field experiments used the Universal moth trap, or Unitrap (AgriSense-BCS Ltd, Pontypridd, UK). This trap is a white bucket with a yellow cone over the bucket top, and a green lid. Each trap included a 2.2 cm 2.2 cm piece of Vaportape (Hercon Environmental Inc., Emigsville, PA) that was stapled to the inside wall of the trap bucket. Lures were placed in a small basket at the centre of the inside of the trap lid. Traps were hung at a height of 2 3 m from branches of apple trees in commercial orchards in Yakima County, Washington. Traps within a set (statistical block) were within an orchard row, and were six trees or 15 m apart, while sets of traps were three rows or 18 m apart. Treatments were randomized when traps were set up. Lures were replaced at 2 weeks and Vaportape was replaced at 4 weeks. Chemicals tested as attractants were loaded into pre-extracted red rubber septa (West Inc., Lyonville, PA), in 2 ll methylene chloride. Septa were air dried in a fume hood for 24 h and were then stored in glass bottles in a freezer until placement in the field. Pheromone blend experiment This experiment tested the hypotheses that males are attracted to (Z7)-14Ac, and that (Z5)-14Ac enhances male response to (Z7)-14Ac. Treatments were: (i) a control septum with no pheromone; (ii) a septum with 1 mg of (Z7)-14Ac alone; and (iii) a septum with 1 mg (Z7)-14Ac and 1 lg (Z5)-14Ac. Five sets of traps, each set including the three treatments, were placed in the field on 23 May 22, in a randomized complete block arrangement. Traps were checked weekly until 6 June 22. This experiment was repeated in 24, with five replicates set up 24 May and maintained until 15 June. Gas chromatography with electroantennographic detection analysis This experiment tested the antennal responses of spotted cutworm male moths to the E and the Z isomers of (5)-14Ac and (7)-14Ac, in order to possibly clarify pheromonal responses of males to the positional and geometric isomers of prior spotted cutworm pheromone reports. One microlitre aliquots of authentic standards were analysed by gas chromatography coupled to electroantennographic detection (GC-EAD) using a Hewlett Packard 589 Series II gas chromatograph and an IDAC 232 data acquisition interface with a micromanipulator assembly type IRN-5 (Syntech, Kirchzarten, Germany). The gas chromatograph was equipped with a DB-1 (Agilent Technologies, Palo Alto, CA) fused silica capillary column [.25 mm (ID) 6 m (length) with.25 lm film thickness] and samples were injected manually in splitless mode. The injector temperature was 25 C and helium was the carrier gas. The column temperature started at 4 C maintained for 2 min, increased to 2 C at a rate of 1 C/min and held at 2 C for 12 min. The effluent from the column was split using an OSS-2 splitter (SGE Analytical Science, Austin, TX) between the flame ionization detector (FID) and the electroantennographic 594 J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA.

P. J. Landolt, C. Guédot and R. S. Zack Spotted cutworm responses to sex pheromone and blacklight detector (EAD) with a ratio FID : EAD of 1 : 2. The make-up gas connected to the splitter was nitrogen driven at a flow rate of 4 ml/min. Adult spotted cutworm moths were captured in a walk-in blacklight trap adjacent to an apple orchard near Donald, in Yakima County, Washington, from late August to early October 26. Larvae were reared on an artificial diet (Southland Products Inc., Lake Village, AR) until they burrowed into soil provided and pupated. Pupae were removed from soil and kept in waxed paper cups at 1 C on a 16L : 8D light cycle and 65 7% RH until adult emergence. Male moths used for GC-EAD analysis were 2 9- day-old virgin males. One antenna per insect was excised at the base of the antennal scape and fixed between two silver electrodes with electrically conductive gel (Spectra 36 electrode gel, Parker Laboratories, Fairfield, NJ). GC-EAD analyses were conducted by exposing male spotted cutworm moth antennae to 1 ll aliquots of 2 ng/ll solutions of each of the synthetic standards; (Z7)-14Ac, (Z5)- 14Ac, (E7)-14Ac, and (E5)-14Ac. Each analysis was replicated using three moths. Geometric isomer experiment Results from the GC-EAD analysis suggested to evaluate moth response to E vs. Z isomers of the combination of (7)-14Ac and (5)-14Ac, as the major and minor components of a blend respectively. Treatments were: (i) 1 mg (Z7)-14Ac + 1 lg (Z5)-14Ac; (ii) 1 mg (Z7)-14Ac + 1 lg (E5)-14Ac; (iii) 1 mg (E7)-14Ac + 1lg (Z5)-14Ac; and (iv) 1 mg (E7)- 14Ac + 1 lg (E5)-14Ac. Five sets of these traps were placed in the field 24 March 28 and were maintained until 6 November 28. Traps were checked weekly. A second test evaluated spotted cutworm moth response in the field to E vs. Z isomers of (7)-14Ac presented singly. Treatments were: (i) a control septum with no pheromone; (ii) 1 mg (Z7)- 14Ac; (iii) 1 mg (E7)-14Ac; (iv) 1 mg (Z7)-14Ac + 1 lg (Z5)-14Ac. Five sets of these traps were placed in the field 17 March 29 and were maintained until 4 November 29. Season long monitoring of spotted cutworm with traps Based on the results of the prior experiments, the blend of (Z7)-14Ac and (Z5)-14Ac in rubber septa at dosages of 1 mg and 1 lg respectively was used to determine seasonality of sex attraction and to verify the seasonal pattern of spotted cutworm moth flight reported by Howell (1979) using blacklight traps. Pheromone traps were then compared to blacklight traps through the growing seasons of 25 through 29. All traps were in or on the edges of commercial apple orchards in Yakima County, Washington. Traps were checked weekly and lures and Vaportape were replaced every 4 weeks. In 25, three pheromone traps and three blacklight traps were compared for monitoring of spotted cutworm. These traps were set up on 31 March and were maintained until 9 November. Blacklights in traps were 8 W blacklight bulbs operated on 12 V DC batteries. Bulbs were mounted at the center of galvanized steel vanes sitting over the funnel of a bucket. VaporTape was placed in the bucket to kill captured moths. Batteries were changed out every 2 days. In 26 and 27, three pheromone traps and a single blacklight trap sampled spotted cutworm moths. In 26, these traps were maintained from 12 April to 28 November. In 27, these traps were maintained from 31 March until 3 November. The blacklight trap used in these two years was a large walk-in cage design, with a cone fitted over a large screened cage. Two 3 W blacklight bulbs were fitted in the centre of aluminium vanes positioned over the cone. These lights were powered by AC power. In 28, three pheromone traps and three blacklight traps were compared for use in monitoring spotted cutworm moths in apple orchards. Traps were maintained from 16 April to 31 October. Blacklight traps were BioQuip (Palo Alto, CA) Blacklight Traps, equipped with 12 W bulbs. In addition, the walk-in light trap described above was maintained and monitored daily for spotted cutworm moths from 1 April to the end of November. In 29, five pheromone traps and a single blacklight trap sampled spotted cutworm moths. These traps were maintained from 17 March to 4 November. The same walk-in blacklight trap described above was maintained and checked weekly for spotted cutworm moths also from 17 March to 4 November. Statistical analyses were performed using Statmost Statistical software (DataMost 1995). For experiments that compared pheromone blends, treatment means were subjected to an anova and differences between means were determined by Tukey s test following a significant F value for the anova. Spotted cutworm moths were identified by comparison to descriptions and photographs in Lafontaine (1998). Voucher specimens of X. c-nigrum are placed in the James Entomological Collection, J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA. 595

Spotted cutworm responses to sex pheromone and blacklight P. J. Landolt, C. Guédot and R. S. Zack Department of Entomology, Washington State University, Pullman, Washington. Results Evaluation of pheromone compounds Pheromone blend experiment No male spotted cutworm moths were captured in unbaited traps. Numbers of males captured in traps baited with (Z7)-14Ac were significantly greater than in unbaited traps for the second test of this experiment. Numbers of males trapped with the combination of (Z5)-14Ac and (Z7)-14Ac were significantly greater than numbers in unbaited traps or in traps baited with (Z7)-14Ac alone. The latter finding was the same for both tests of this experiment (table 1). Gas chromatography with electroantennographic detection analysis All four synthetic standards, (Z7)-14Ac, (E7)-14Ac, (Z5)14Ac, and (E5)-14Ac, elicited consistent antennal responses in male spotted cutworm moths. Geometric isomer experiment Numbers of male spotted cutworm moths caught in traps baited with the combinations of (E7)-14Ac + (Z5)-14Ac or (E7)-14Ac + (E5)-14Ac were few and were not significantly different from the numbers captured in unbaited traps (table 2). However, numbers of males captured in traps baited with (Z7)- 14Ac + (Z5)-14Ac, or (Z7)-14Ac + (E5)-14Ac, were significantly greater than unbaited traps. Catches were greatest in traps baited with (Z7)-14Ac + (Z5)- 14Ac compared to all other treatments (table 2). In the second test, numbers of male spotted cutworm moths caught in traps baited with the combinations of (Z7)-14Ac + (Z5)-14Ac were significantly greater than the numbers captured in unbaited traps, traps baited with either (E7)-14Ac alone or (Z7)-14Ac alone (table 3). Traps baited with (Z7)-14Ac caught more males than traps baited with (E7)-14Ac alone or unbaited traps. No male spotted cutworms were caught in unbaited traps or in traps baited with (E7)-14Ac alone (table 3). Season long monitoring of spotted cutworm with traps Catches of moths in pheromone traps maintained near Yakima in 25 through 29 indicated two general flight periods of spotted cutworm moths through the season (fig. 1). These periods of responses to pheromone traps were consistent through the years. The greatest numbers of males captured in pheromone traps were in spring, from early May into early June. A second later period of activity, generally from late July into late October/ early November, was evident, but with reduced numbers of moths in pheromone traps. There was not a consistent and distinct single peak of catches during this period. Catches of spotted cutworm moths in blacklight traps also indicated two periods of activity, one in June and one in August into early Table 2 Mean numbers of male spotted cutworm moths captured in traps baited with combinations of putative female pheromone components (n = 5) (Yakima County, WA) Treatment Mean SE Control..a (Z7)-14Ac + (Z5)-14Ac 21. 31.1b (Z7)-14Ac + (E5)-14Ac 13.4 3.2c (E7)-14Ac + (Z5)-14Ac.8.8a (E7)-14Ac + (E5)-14Ac.4.4a Means followed by the same letter are not significantly different by Tukey s test at P <.5. Table 1 Mean numbers of male spotted cutworm moths captured in traps baited with two putative female pheromone components, singly and in combination. Test 1 was conducted in May/June 22 (n = 5). Test 2 was conducted in June 24 (n = 5) (Yakima County, WA) Treatment Test 1 Test 2 Mean SE Mean SE Control..a..a (Z7)-14Ac.2.2a 2.4 1.9b (Z7)-14Ac + (Z5)-14Ac 39.2 7.8b 23.2 8.1c Means in a column followed by the same letter are not significantly different by Tukey s test at P <.5. Table 3 Mean numbers of male spotted cutworm moths captured in traps baited with putative female pheromone components (n = 5) (Yakima County, WA) Treatment Mean SE Control..a (E7)-14Ac..a (Z7)-14Ac 7.6 2.1b (Z7)-14Ac + (Z5)-14Ac 13.8 11.6c Means followed by the same letter are not significantly different by Tukey s test at P <.5. 596 J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA.

P. J. Landolt, C. Guédot and R. S. Zack Spotted cutworm responses to sex pheromone and blacklight 15 25 SCW seasonality to blacklight 8 25 SCW seasonality to pheromone Female 12 9 6 3 Male 64 48 32 16 13 117 131 145 159 173 187 21 215 229 243 257 271 285 299 313 327 13 117 131 145 159 173 187 21 215 229 243 257 271 285 299 313 327 1 8 6 4 2 26 SCW seasonality to blacklight 26 SCW seasonality to pheromone 8 Female Male 64 48 32 16 18 122 134 151 165 179 193 27 221 234 248 263 275 29 34 318 332 18 122 134 151 165 179 193 27 221 235 249 263 276 29 34 318 332 12 96 72 48 24 27 SCW seasonality to blacklight 15 27 SCW seasonality to pheromone Female Male 12 9 6 3 13 117 131 145 159 173 187 21 215 229 243 257 272 285 299 313 327 13 117 131 145 159 173 187 21 215 229 243 257 271 285 299 313 327 5 4 3 2 1 28 SCW seasonality to blacklight 28 SCW seasonality to pheromone 12 weeks female 12 weeks male 3 weeks female 3 weeks male 16 128 96 64 32 16 121 136 151 165 179 191 25 219 233 247 261 275 289 35 319 16 121 137 151 165 179 192 26 22 234 248 262 275 289 35 319 5 4 3 2 1 29 SCW seasonality to blacklight 29 SCW seasonality to pheromone 4 Female Male 32 24 16 8 15 119 133 147 161 175 189 23 217 231 245 259 273 287 31 315 15 119 133 147 161 175 189 23 217 231 245 259 273 287 31 315 329 Fig. 1 Mean ( SE) numbers of spotted cutworm moths captured per week in traps baited with sex pheromone and in blacklight traps, for the 25 to 29 seasons (Yakima County, WA). J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA. 597

Spotted cutworm responses to sex pheromone and blacklight P. J. Landolt, C. Guédot and R. S. Zack September. Patterns of catches of males and females in blacklight traps were generally similar between years (fig. 1), although in most years, the number of males captured exceeded the number of females captured. Although not distinctly different from the pattern in timing seen with pheromone traps, the pattern of moths in blacklight traps did not closely match that of pheromone traps. The peak in catches in blacklight traps in August was not coincident with highest sex pheromone trap activity, which lacked a consistent or distinct peak at that time. Numbers of spotted cutworm moths captured in blacklight traps were very small compared to numbers in pheromone traps during the spring flight, but in August numbers in blacklight traps were larger compared to those in pheromone traps (fig. 1). Discussion Roelofs and Comeau (1971) first reported trapping male spotted cutworm moths with (Z7)-14Ac. The capture of X. c-nigrum in traps baited with (Z7)-14Ac was also reported by Bestmann et al. (1979), Hirai (1976), Ando (1977) and Steck et al. (1982). Steck et al. (1982) in Saskatchewan, Canada, captured increased numbers of males of X. c-nigrum in traps baited with the combination of (Z5)-14Ac and (Z7)- 14Ac, compared to (Z7)-14Ac alone. However, in Europe, (Z5)-14Ac inhibited male spotted cutworm response to (Z7)-14Ac (Subchev et al. 1996). Mayer and McLaughlin (1991) suggested that the moth may vary in its pheromone communication with geography. The contradiction in prior reports of the role of (Z5)-14Ac in sex attraction indicated a need to verify responses of local spotted cutworm moths to these compounds. In this study, the first trapping experiment assessed male spotted cutworm moth attraction to two positional isomers of tetradecenyl acetate, (Z5)- 14Ac and (Z7)-14Ac, that have been implicated in sex attraction of that species (Steck et al. 1979, 1982). Results of the first test of this experiment (May/June 22) did not show a significant rate of capture of males in traps baited with (Z7)-14Ac. However, the second test of this experiment (June 24) did demonstrate attraction of males of X. c-nigrum to (Z7)-14Ac. The reason for the absence of a significant response to (Z7)-14Ac in the first test (May 22) is unknown. Both tests of our first trapping experiment showed a stronger response of males to the combination of (Z7)-14Ac and (Z5)- 14Ac, compared to (Z7) 14Ac alone, confirming locally the results reported by Steck et al. (1982) working in Canada, but contrary to the findings of Subchev et al. (1996) in Europe. The objective of the second and third experiments was to clarify spotted cutworm moth responses to pheromone geometric isomers. Roelofs and Comeau (197, 1971), working in New York, captured males of the small form of spotted cutworm (X. adela = c-nigrum) with the E isomer and the larger form of the moth (X. dolosa) with the Z isomer of (7)- 14Ac. These reports contradict other studies that trapped X. c-nigrum with (Z7)-14Ac (Ando 1977; Bestmann et al. 1979; Steck et al. 1979, 1982). Our results showed antennal responses to the Z and the E isomers of both (7)-14Ac and (5)-14Ac. However, in the field, testing of these same compounds indicated responses only to the Z isomers. The response seen to (Z7)-14Ac + (E5)-14Ac may be a response to (Z7)-14Ac alone, since it is quantitatively less than the response to (Z7)-14Ac + (Z5)-14Ac. At the least, the presence of (E5)-14Ac did not shut down male response to (Z7)-14Ac. Again, best results were obtained using (Z7)-14Ac + (Z5)-14Ac. Although it was our intention to use these experimental results to make recommendations on the monitoring of spotted cutworm in apple orchards, observations of the spotted cutworm seasonal presence in traps raised questions about the moth responses to pheromone vs. blacklight. The trapping patterns differed from prior reports and also showed differences between patterns of response to blacklight vs. pheromone. At this time, we do not know if pheromone traps or blacklight traps might best provide a more accurate assessment of relative populations of spotted cutworm moths or of the risks of damage to crops by the larvae. The seasonal monitoring of spotted cutworm using both light traps and pheromone traps from 25 to 29 were quite consistent from year to year. However, they showed inconsistencies in patterns of moth activity compared to that reported by Howell (1979) for 1973 to 1977 using blacklight traps. Differences in patterns relate to: (i) time frames or dates covered by captures of moths; (ii) rates of capture of moths in traps; and (iii) relationship between population sizes indicated by captures of moths in the first and later flight(s). Captures of moths in blacklight traps reported by Howell (1979) lasted longer for both flights compared to our blacklight trap catches. For the first flight, Howell (1979) reported a 6 1 week flight while we report a 4 7 week flight. For the second flight, captures of moths by Howell (1979) were mainly over 11 13 weeks, compared to 5 7 weeks in 598 J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA.

P. J. Landolt, C. Guédot and R. S. Zack Spotted cutworm responses to sex pheromone and blacklight our study. It is possible that this apparent difference in breadths of activity may be due to differences in numbers of moths trapped per unit time (peak amplitude), which could then broaden the period of detectable activity at the beginning and ending of flights. Captures of spotted cutworm moths in blacklight traps in our study were dramatically lower than captures reported by Howell (1979). Populations of spotted cutworms may have been much greater in the Yakima Valley during the 197s compared to recently. Spotted cutworms are polyphagous, feeding on many plants including a variety of crops. Population densities can be strongly impacted by local and regional makeup of cropping systems and pest management practices on those crops. However, we are not aware of what changes in crops or pest management practices would result in large changes of spotted cutworm numbers for this time frame. Our light trap catches were consistent with Howell (1979) in showing a second flight period of spotted cutworm moths that gave consistently higher trap catches compared to the earlier spring flight. However, from 25 to 29, there was a strong difference between the strength or amplitude of the spotted cutworm numbers trapped with blacklight in comparison to sex pheromone. Compared to blacklight traps, there were more moths trapped with pheromone in the spring flight and consistently smaller numbers of moths trapped with pheromone later in the summer. Similar differential responses to pheromone vs. blacklight, with greater responses to pheromone earlier and greater responses to blacklight later in the season, were reported for codling moth, Cydia pomonella (L.), by Howell (1981) and for corn earworm, Helicoverpa zea (Boddie), by Roach (1975). Possible explanations for this disparity in trapping the spotted cutworm relate to differential environmental conditions or genetic strains. Morton et al. (1981) for example found that Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) response to blacklight traps was influenced by wind speed, temperature, night length and moonlight. Spring conditions in Washington include much cooler night-time temperatures which may prompt moths to fly before or at dusk, when background lighting can interfere more with responses to blacklight traps. Such a phenomenon could make pheromone traps appear more effective during spring than in summer. Alternatively, the spotted cutworm may yet have more than one pheromone strain in the Yakima Valley, with one strain responding strongly to the combination of Z-7-14Ac + Z-5-14Ac in spring and late summer and another strain that responds poorly to that blend flying in August. Both these explanations are speculative and additional study is called for to determine why spotted cutworm responses to these stimuli differ through the season and which type of trap, if either, more accurately reflects spotted cutworm density. Studies of spotted cutworm behaviour and sex attraction have been complicated by issues of taxonomy and identity. The taxonomy is recently summarized by Lafontaine (1998). Most Eurasian and North American specimens are presently under the same specific name (c-nigrum), but were previously under the names c-nigrum and adela respectively. Until 198, the two North American forms now called c-nigrum and dolosa (Franclemont 198) were together under the name c-nigrum. Xestia dolosa differs from X. c-nigrum both in size and in female genital morphology. The former is known only from eastern North America, while the latter is much more widespread from coast to coast and from Alaska to Central America. At this time, all spotted cutworms in Washington are placed under one name, X. c-nigrum. Results of our tests locally with different pheromone lures do not indicate the presence of more than one pheromonal phenotype of spotted cutworms. There was no indication in the Yakima Valley of a moth response to the E isomers of the pheromone blend, as reported by Roelofs and Comeau (1971) in New York, where the smaller form (adela) responded to (E7)-14Ac and the larger form (dolosa) to (Z7)-14Ac. Also, there was no indication of an inhibitory effect of (Z5)-14Ac on moth response to (Z7)-14Ac, as was seen in Europe by Subchev et al. (1996). The differences however that we observed in spotted cutworm moth seasonal response to sex attractant lures vs. blacklights could indicate the presence of more than one spotted cutworm in the Yakima Valley, with differing phenologies and differing sex pheromone responses. If this is indeed the case, it will be very important to determine if there are corresponding differences in spotted cutworm pest status on a variety of crops in this area and when those spotted cutworms might require pest management intervention. Acknowledgements Technical assistance was provided by Robert Brown, Jewel Brumley, Jennifer Friedt, Daryl Green, Stephanie Jesperson, Bonnie Ohler, Karolynn Tom, and Laura Tom. This research was funded in part by grants from the Washington Tree Fruit Research J. Appl. Entomol. 135 (211) 593 6 Published 21. This article is a US Government work and is in the public domain in the USA. 599

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