Journal of Chemical Ecology, Vol. 15, No. 6, 1989
INFLUENCE OF PHEROMONE TRAP COLOR AND DESIGN ON CAPTURE OF MALE VELVETBEAN CATERPILLAR A N D FALL ARMYWORM MOTHS (LEPIDOPTERA: NOCTUIDAE) 1
EVERETT
R. MITCHELL, and ROBERT
HERNDON
R. AGEE,
R. HEATH
Insect Attractant, Behavior, and Basic Biology Research Laboratory Agricultural Research Service, U.S. Department of Agriculture Gainesville, Florida 32604 (Received May 2, 1988; accepted August 18, 1988)
Abstraet--Three pheromone traps were evaluated in paired field trials for effectiveness in capturing wild male velvetbean caterpillar moths (VBC), Anticarsia gemmatalis Hrbner, and fall armyworm moths (FAW), Spodopterafrugiperda (J.E. Smith), using a wind-oriented trapping device. The traps were: (1) the standard multicolored bucket trap consisting of a forest green canopy, yellow funnel, white bucket and open (i.e., single wire) pheromone holder; (2) a forest green monocolored bucket trap; and (3) the Multi-Pher1 trap consisting of a blue-green canopy, white funnel, white bucket, and white, multislotted pheromone holder. The Multi-Pher-1 trap differs primarily from the other two in that its entrance is smaller in diameter and is partially obstructed by the pheromone holder. Significantly fewer VBC and FAW males were captured in pheromone-baited monocolored (forest green) bucket traps than standard multicolored bucket traps. The Multi-Pher-1 trap also caught significantly fewer VBC moths than the standard multicolored bucket trap, but there was no significant difference in numbers of FAW moths caught in the two traps. The results further demonstrate the importance of considering visual cues, in this case color, in the design of pheromone traps for nocturnal insects. Key Words--Trap color, trap design, velvetbean caterpillar, Anticarsia gemmatalis, fall armyworm moth, Spodoptera frugiperda, Lepidoptera, Noctuidae, electroretinogram. l This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by USDA. 1775
1776
MITCHELL ET AL. INTRODUCTION
Intemational Pheromones Moth Traps (bucket trap; Intemational Pheromone Systems, Merseyside, England) baited with pheromone are used widely to survey adult populations of the fall armyworm (FAW), Spodopterafrugiperda (J.E. Smith) (Mitchell et al., 1985). Mitchell and Heath (1986) also demonstrated the utility of bucket traps for surveying adult populations of the velvetbean caterpillar (VBC), Anticarsia gemmatalis Hfibner, with sex pheromone. In the course of these and subsequent investigations involving pheromones of the FAW, VBC, and Heliothis spp., we observed a propensity for bumblebees, Bombus sp., to be captured in bucket traps along with the target species. Captures of bumblebees were most common in late summer and fall when the traps were deployed in weedy areas with plants having large conspicuous blooms. We attributed the apparent attraction of bumblebees to the bucket trap's colorful appearance--a protective canopy of forest green, an entrance funnel of bright yellow, and a white bucket receptacle. Bucket traps of identical dimensions also are available with one color throughout--forest green. The present study was designed to determine if the forest green bucket trap could be used in place of the multicolored bucket trap without sustaining significant reductions in captures of male FAW or VBC moths. We also evaluated the Multi-Pher-1 (BioControle Services, Ste-Foy, Canada), a trap somewhat similar in design to the bucket trap but costing approximately 30% less. This trap has a blue-green canopy, white funnel, white bucket, and white, multislotted pheromone holder. The design of the Multi-Pher-1 trap differs from the standard multicolored bucket trap in that the entrance is smaller, the funnel is abbreviated, and the funnel opening is partially obstructed by the pheromone holder.
METHODS AND MATERIALS
Field Trials. All tests were conducted in northwest Alachua County, Florida, in fall 1987. Pheromone baits for the FAW were prepared by Terochem Laboratories, Ltd. (Alberta, Canada). The four-component pheromone blend formulated on rubber septa at 2.0 mg/dispenser consisted of (percentage by weight): (Z)-7-dodecen-l-ol acetate, 0.45 %; (Z)-9-dodecen-l-ol acetate, 0.25 %; (Z)-9-tetradecen-l-ol acetate, 81.61%; and (Z)-I 1-hexadecen-l-ol acetate, 17.69%. The pheromone used in tests with the VBC was prepared in our laboratory. The pheromone was purified by AgNO3 high-performance liquid chromatography (Heath and Sonnet, 1980). Analysis of the purified pheromone was obtained on a capillary gas chromatograph (Varian 3700), and the columns used for analysis were 50 m • 0.25 mm ID methyl silicone (OV-1); 50 m • 0.25 mm ID Carbowax 20 M; and 42 m • 0.27 mm ID cholesteryl-p-chlorocinna-
TRAP COLOR AND DESIGN AFFECTS MOTH C A P T U R E
1777
mate, a liquid crystal phase described by Heath et al. (1979). Analysis of the pheromone with these columns showed the material to be at least 99 % pure. Before loading, the rubber septa (5 x 9 mm; No. 8753-D22, A.H. Thomas, Philadelphia, Pennsylvania) were extracted with CHzC12 for 24 hr and air dried. A septum was loaded by depositing 0.5 mg of a blend consisting of (Z,Z,Z)3,6,9-eicosatriene and (Z,Z,Z)-3,6,9-heneicosatriene (40 and 60%, respectively) dissolved in 100 txl hexane into the end with the largest reservoir. Wind-oriented traps (WORT) (Mitchell et al., 1988) were used to make simultaneous comparisons of the bucket trap combinations (standard multicolored vs. forest green, Figure la) or the standard multicolored bucket trap and the Multi-Pher 1 trap (Figure lb). The WORT consists of three major compo-
FIG. 1. Wind-oriented trapping device (WORT) used to determine the effect of color (a) and design (b) on capture of male velvetbean caterpillar and fall armyworm moths in traps baited with sex pheromone. (a) International Pheromones bucket traps (BT) mounted on WORT (left, standard BT, with forest green top, yellow funnel, and white bucket; BT on right is forest green throughout). (b) Standard BT on right and MultiPher-1 trap on left.
1778
MITCHELL ET AL.
nents: tail and nose assembly, pivot, and support arms arranged perpendicularly to the tail and nose sections. The design of the WORT is such that treatments are always aligned in the same relationship relative to the prevailing wind, thereby minimizing the possibility of interactions among closely spaced pheromone traps caused by shifts in surface winds. The test traps were positioned 1 m apart opposite each other on the WORT support arms. WORTs were positioned so that the bottom of each trap bucket was ca. 1 m from the soil surface. The bucket receptacle of each trap contained a small piece of dichlorovos (Vapona) insecticide strip that served as a killing agent for trapped moths. Three WORTs baited with VBC pheromone and three WORTs baited with FAW pheromone were operated simultaneously in a soybean field ( > 35 hectares) that also had a high population of young (pretassel) volunteer corn plants. The WORTs were spaced 300-500 m apart throughout the field. In the first test with the VBC, the standard multicolored bucket trap (forest green canopy, yellow funnel, white bucket, Figure 2a) was compared to the monocotored forest green bucket trap (not shown). The first trial with the FAW involved the same trap color combinations on different WORTs and was carded out simulta-
FIG. 2. Trap components: (a) multicolored bucket trap with forest green canopy, yellow funnel, white bucket; (b) Multi-Pher-1 trap with blue-green canopy, white pheromone holder, white funnel and bucket.
TRAP COLOR AND DESIGN AFFECTS MOTH CAPTURE
1779
neously with the first VBC trap test. The second test for both the VBC and FAW compared the standard bucket trap with the Multi-Pher-1 trap (blue-green canopy, white multislotted pheromone holder, white funnel, white bucket) (Figure 2b). These trials also were carried out simultaneously. In all cases, the trap colors were an integral part of each molded component, i.e., the colors were not simply painted onto the component's exterior surfaces. Moth catches were recorded daily, and the treatments (i.e., traps) were rotated between positions on each WORT. Pheromone baits were replaced every two weeks. Each collection was considered a replicate. Differences between means were separated using the t test for paired treatments (Steel and Torrie, 1960). Spectral Analysis of Compound Eye. Spectral sensitivity of the compound eye of male VBC and FAW moths (six of each) to monochromatic light at wavelengths from 350 to 675 nm was measured electrophysiologically. The moths were from cultures reared in our laboratory on a modified pinto bean diet (Guy et al., 1985). The moths were 2-3 days old when tested. The moths were immobilized on a wax base to facilitate the insertion of microelectrodes into their compound eyes. A recording stainless-steel microelectrode was inserted 20-30/zm into the mid-dorsal region of one eye that was positioned with the mid-lateral center directed toward the stimulating light. The indifferent electrode was positioned in a similar position in the unilluminated eye. A light beam from a monochromator was focused directly on the lateral surface of the eye and head of the moth. The moths were dark-adapted for 45-60 min until they were at maximum sensitivity in a light-proof electrically shielded cage. The electroretinogram techniques were similar to those described by Agee (1973) and Agee and Patterson (1983). Light pulses of 200 msec were delivered at a rate of one per 2 sec and intensity adjusted to produce a "criterion" electrical response of 200 IxV in the eye per stimulus. The light pulse duration was controlled by an electrically driven solenoid shutter. Monochromatic light was produced by a quartz-halogen lamp with intensity adjusted to the criterion response by quartz-iconel neutral density wedge and filters. The intensity of light stimuli was determined at all test wavelengths with a calibrated thermopile (accuracy traceable to National Bureau of Standards) and a nanovolt meter in microwatts per square centimeter. Test wavelengths from 350 to 675 nm were selected with a grating monochromator. The electrical responses generated by the photoreceptors in the eye were amplified with a biological amplifier and displayed on an oscilloscope for analysis. Spectral Reflectance of Trap Colors. The spectral reflectance of samples (2.5 cm x 2.5 cm) of the various colored trap components were determined using a Varian 634S recording reflectance spectrophotometer. The surfaces were scanned at wavelengths from 330 to 850 nm with the monochromator slit width set at 1 mm and operated at a scan rate of 50 nm/min to obtain maximum accuracy. Eastman Kodak white (No. 6091)was the 100% standard.
1780
MITCHELL ET AL. RESULTS AND DISCUSSION
Color had a profound effect on pheromone trap effectiveness in capturing male VBC moths (Figure 3A). The standard multicolored bucket trap captured 6.7 times more VBC moths than the forest green bucket trap (difference significant at P < 0.01, paired t test). The standard multicolored bucket trap also captured significantly more male FAW moths than the forest green bucket trap (Figure 4A; P < 0.01), although the magnitude of increase was not as great as for the VBC. The standard multicolored bucket trap captured significantly more (P < 0.01; Figure 3B) male VBC moths than the Multi-Pher-1 trap. However, there was no significant difference in the numbers of FAW males captured in the standard multicolored bucket trap and the Multi-Pher-1 trap (Figure 4B). The spectral reflectance of the standard multicolored bucket trap parts showed that white had 91-100% reflection at wavelengths from 420 to 680 nm. The yellow reflected 55 % of the incident light at wavelengths from 530 to 680 rim. The forest green had a reflectance peak at 510-530 nm of only 16 % of the incident light. By contrast the blue-green canopy of the Multi-Pher-1 trap reflected 43 % of the incident light at wavelengths of 480-510 nm (Figure 5). The eyes of both the VBC and FAW were most sensitive at two similar peaks: a broad major peak in the green-yellow range from 480 to 570 nm (Fig125 er" --n b-CI2 a_
I
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FIG. 3. Capture of male velvetbean caterpillar moths in: (A) standard bucket trap (BT) versus the all-green BT trap (33 replications); (B) standard BT versus the Multi-Pher-1 trap (21 replications). Difference between means within A and B were significant, P < 0.01, paired t test. Thin black bars represent standard error of the mean.
1781
TRAP COLOR AND DESIGN AFFECTS MOTH CAPTURE
20 r"m W -m I.--. Q.L.3 r..,'3 LU J C]Z ~E
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GREEN
V U _ T I -PHER
STRNEIRRD
F~G. 4. Capture of male fall armyworm moths in: (A) standard bucket trap (BT) versus the all-green BT (43 replications); (B) standard BT versus Multi-Pher-1 trap (22 replications). Difference in mean moth captured within A was significant, P < 0.01, paired t test; difference in mean moth captured within B was not significant. Thin black bars represent standard error of the mean.
100 m (J Z
~
INFLUENCE OF PHEROMONE TRAP COLOR AND DESIGN ON CAPTURE OF MALE VELVETBEAN CATERPILLAR A N D FALL ARMYWORM MOTHS (LEPIDOPTERA: NOCTUIDAE) 1
EVERETT
R. MITCHELL, and ROBERT
HERNDON
R. AGEE,
R. HEATH
Insect Attractant, Behavior, and Basic Biology Research Laboratory Agricultural Research Service, U.S. Department of Agriculture Gainesville, Florida 32604 (Received May 2, 1988; accepted August 18, 1988)
Abstraet--Three pheromone traps were evaluated in paired field trials for effectiveness in capturing wild male velvetbean caterpillar moths (VBC), Anticarsia gemmatalis Hrbner, and fall armyworm moths (FAW), Spodopterafrugiperda (J.E. Smith), using a wind-oriented trapping device. The traps were: (1) the standard multicolored bucket trap consisting of a forest green canopy, yellow funnel, white bucket and open (i.e., single wire) pheromone holder; (2) a forest green monocolored bucket trap; and (3) the Multi-Pher1 trap consisting of a blue-green canopy, white funnel, white bucket, and white, multislotted pheromone holder. The Multi-Pher-1 trap differs primarily from the other two in that its entrance is smaller in diameter and is partially obstructed by the pheromone holder. Significantly fewer VBC and FAW males were captured in pheromone-baited monocolored (forest green) bucket traps than standard multicolored bucket traps. The Multi-Pher-1 trap also caught significantly fewer VBC moths than the standard multicolored bucket trap, but there was no significant difference in numbers of FAW moths caught in the two traps. The results further demonstrate the importance of considering visual cues, in this case color, in the design of pheromone traps for nocturnal insects. Key Words--Trap color, trap design, velvetbean caterpillar, Anticarsia gemmatalis, fall armyworm moth, Spodoptera frugiperda, Lepidoptera, Noctuidae, electroretinogram. l This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by USDA. 1775
1776
MITCHELL ET AL. INTRODUCTION
Intemational Pheromones Moth Traps (bucket trap; Intemational Pheromone Systems, Merseyside, England) baited with pheromone are used widely to survey adult populations of the fall armyworm (FAW), Spodopterafrugiperda (J.E. Smith) (Mitchell et al., 1985). Mitchell and Heath (1986) also demonstrated the utility of bucket traps for surveying adult populations of the velvetbean caterpillar (VBC), Anticarsia gemmatalis Hfibner, with sex pheromone. In the course of these and subsequent investigations involving pheromones of the FAW, VBC, and Heliothis spp., we observed a propensity for bumblebees, Bombus sp., to be captured in bucket traps along with the target species. Captures of bumblebees were most common in late summer and fall when the traps were deployed in weedy areas with plants having large conspicuous blooms. We attributed the apparent attraction of bumblebees to the bucket trap's colorful appearance--a protective canopy of forest green, an entrance funnel of bright yellow, and a white bucket receptacle. Bucket traps of identical dimensions also are available with one color throughout--forest green. The present study was designed to determine if the forest green bucket trap could be used in place of the multicolored bucket trap without sustaining significant reductions in captures of male FAW or VBC moths. We also evaluated the Multi-Pher-1 (BioControle Services, Ste-Foy, Canada), a trap somewhat similar in design to the bucket trap but costing approximately 30% less. This trap has a blue-green canopy, white funnel, white bucket, and white, multislotted pheromone holder. The design of the Multi-Pher-1 trap differs from the standard multicolored bucket trap in that the entrance is smaller, the funnel is abbreviated, and the funnel opening is partially obstructed by the pheromone holder.
METHODS AND MATERIALS
Field Trials. All tests were conducted in northwest Alachua County, Florida, in fall 1987. Pheromone baits for the FAW were prepared by Terochem Laboratories, Ltd. (Alberta, Canada). The four-component pheromone blend formulated on rubber septa at 2.0 mg/dispenser consisted of (percentage by weight): (Z)-7-dodecen-l-ol acetate, 0.45 %; (Z)-9-dodecen-l-ol acetate, 0.25 %; (Z)-9-tetradecen-l-ol acetate, 81.61%; and (Z)-I 1-hexadecen-l-ol acetate, 17.69%. The pheromone used in tests with the VBC was prepared in our laboratory. The pheromone was purified by AgNO3 high-performance liquid chromatography (Heath and Sonnet, 1980). Analysis of the purified pheromone was obtained on a capillary gas chromatograph (Varian 3700), and the columns used for analysis were 50 m • 0.25 mm ID methyl silicone (OV-1); 50 m • 0.25 mm ID Carbowax 20 M; and 42 m • 0.27 mm ID cholesteryl-p-chlorocinna-
TRAP COLOR AND DESIGN AFFECTS MOTH C A P T U R E
1777
mate, a liquid crystal phase described by Heath et al. (1979). Analysis of the pheromone with these columns showed the material to be at least 99 % pure. Before loading, the rubber septa (5 x 9 mm; No. 8753-D22, A.H. Thomas, Philadelphia, Pennsylvania) were extracted with CHzC12 for 24 hr and air dried. A septum was loaded by depositing 0.5 mg of a blend consisting of (Z,Z,Z)3,6,9-eicosatriene and (Z,Z,Z)-3,6,9-heneicosatriene (40 and 60%, respectively) dissolved in 100 txl hexane into the end with the largest reservoir. Wind-oriented traps (WORT) (Mitchell et al., 1988) were used to make simultaneous comparisons of the bucket trap combinations (standard multicolored vs. forest green, Figure la) or the standard multicolored bucket trap and the Multi-Pher 1 trap (Figure lb). The WORT consists of three major compo-
FIG. 1. Wind-oriented trapping device (WORT) used to determine the effect of color (a) and design (b) on capture of male velvetbean caterpillar and fall armyworm moths in traps baited with sex pheromone. (a) International Pheromones bucket traps (BT) mounted on WORT (left, standard BT, with forest green top, yellow funnel, and white bucket; BT on right is forest green throughout). (b) Standard BT on right and MultiPher-1 trap on left.
1778
MITCHELL ET AL.
nents: tail and nose assembly, pivot, and support arms arranged perpendicularly to the tail and nose sections. The design of the WORT is such that treatments are always aligned in the same relationship relative to the prevailing wind, thereby minimizing the possibility of interactions among closely spaced pheromone traps caused by shifts in surface winds. The test traps were positioned 1 m apart opposite each other on the WORT support arms. WORTs were positioned so that the bottom of each trap bucket was ca. 1 m from the soil surface. The bucket receptacle of each trap contained a small piece of dichlorovos (Vapona) insecticide strip that served as a killing agent for trapped moths. Three WORTs baited with VBC pheromone and three WORTs baited with FAW pheromone were operated simultaneously in a soybean field ( > 35 hectares) that also had a high population of young (pretassel) volunteer corn plants. The WORTs were spaced 300-500 m apart throughout the field. In the first test with the VBC, the standard multicolored bucket trap (forest green canopy, yellow funnel, white bucket, Figure 2a) was compared to the monocotored forest green bucket trap (not shown). The first trial with the FAW involved the same trap color combinations on different WORTs and was carded out simulta-
FIG. 2. Trap components: (a) multicolored bucket trap with forest green canopy, yellow funnel, white bucket; (b) Multi-Pher-1 trap with blue-green canopy, white pheromone holder, white funnel and bucket.
TRAP COLOR AND DESIGN AFFECTS MOTH CAPTURE
1779
neously with the first VBC trap test. The second test for both the VBC and FAW compared the standard bucket trap with the Multi-Pher-1 trap (blue-green canopy, white multislotted pheromone holder, white funnel, white bucket) (Figure 2b). These trials also were carried out simultaneously. In all cases, the trap colors were an integral part of each molded component, i.e., the colors were not simply painted onto the component's exterior surfaces. Moth catches were recorded daily, and the treatments (i.e., traps) were rotated between positions on each WORT. Pheromone baits were replaced every two weeks. Each collection was considered a replicate. Differences between means were separated using the t test for paired treatments (Steel and Torrie, 1960). Spectral Analysis of Compound Eye. Spectral sensitivity of the compound eye of male VBC and FAW moths (six of each) to monochromatic light at wavelengths from 350 to 675 nm was measured electrophysiologically. The moths were from cultures reared in our laboratory on a modified pinto bean diet (Guy et al., 1985). The moths were 2-3 days old when tested. The moths were immobilized on a wax base to facilitate the insertion of microelectrodes into their compound eyes. A recording stainless-steel microelectrode was inserted 20-30/zm into the mid-dorsal region of one eye that was positioned with the mid-lateral center directed toward the stimulating light. The indifferent electrode was positioned in a similar position in the unilluminated eye. A light beam from a monochromator was focused directly on the lateral surface of the eye and head of the moth. The moths were dark-adapted for 45-60 min until they were at maximum sensitivity in a light-proof electrically shielded cage. The electroretinogram techniques were similar to those described by Agee (1973) and Agee and Patterson (1983). Light pulses of 200 msec were delivered at a rate of one per 2 sec and intensity adjusted to produce a "criterion" electrical response of 200 IxV in the eye per stimulus. The light pulse duration was controlled by an electrically driven solenoid shutter. Monochromatic light was produced by a quartz-halogen lamp with intensity adjusted to the criterion response by quartz-iconel neutral density wedge and filters. The intensity of light stimuli was determined at all test wavelengths with a calibrated thermopile (accuracy traceable to National Bureau of Standards) and a nanovolt meter in microwatts per square centimeter. Test wavelengths from 350 to 675 nm were selected with a grating monochromator. The electrical responses generated by the photoreceptors in the eye were amplified with a biological amplifier and displayed on an oscilloscope for analysis. Spectral Reflectance of Trap Colors. The spectral reflectance of samples (2.5 cm x 2.5 cm) of the various colored trap components were determined using a Varian 634S recording reflectance spectrophotometer. The surfaces were scanned at wavelengths from 330 to 850 nm with the monochromator slit width set at 1 mm and operated at a scan rate of 50 nm/min to obtain maximum accuracy. Eastman Kodak white (No. 6091)was the 100% standard.
1780
MITCHELL ET AL. RESULTS AND DISCUSSION
Color had a profound effect on pheromone trap effectiveness in capturing male VBC moths (Figure 3A). The standard multicolored bucket trap captured 6.7 times more VBC moths than the forest green bucket trap (difference significant at P < 0.01, paired t test). The standard multicolored bucket trap also captured significantly more male FAW moths than the forest green bucket trap (Figure 4A; P < 0.01), although the magnitude of increase was not as great as for the VBC. The standard multicolored bucket trap captured significantly more (P < 0.01; Figure 3B) male VBC moths than the Multi-Pher-1 trap. However, there was no significant difference in the numbers of FAW males captured in the standard multicolored bucket trap and the Multi-Pher-1 trap (Figure 4B). The spectral reflectance of the standard multicolored bucket trap parts showed that white had 91-100% reflection at wavelengths from 420 to 680 nm. The yellow reflected 55 % of the incident light at wavelengths from 530 to 680 rim. The forest green had a reflectance peak at 510-530 nm of only 16 % of the incident light. By contrast the blue-green canopy of the Multi-Pher-1 trap reflected 43 % of the incident light at wavelengths of 480-510 nm (Figure 5). The eyes of both the VBC and FAW were most sensitive at two similar peaks: a broad major peak in the green-yellow range from 480 to 570 nm (Fig125 er" --n b-CI2 a_
I
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FIG. 3. Capture of male velvetbean caterpillar moths in: (A) standard bucket trap (BT) versus the all-green BT trap (33 replications); (B) standard BT versus the Multi-Pher-1 trap (21 replications). Difference between means within A and B were significant, P < 0.01, paired t test. Thin black bars represent standard error of the mean.
1781
TRAP COLOR AND DESIGN AFFECTS MOTH CAPTURE
20 r"m W -m I.--. Q.L.3 r..,'3 LU J C]Z ~E
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GREEN
V U _ T I -PHER
STRNEIRRD
F~G. 4. Capture of male fall armyworm moths in: (A) standard bucket trap (BT) versus the all-green BT (43 replications); (B) standard BT versus Multi-Pher-1 trap (22 replications). Difference in mean moth captured within A was significant, P < 0.01, paired t test; difference in mean moth captured within B was not significant. Thin black bars represent standard error of the mean.
100 m (J Z
~
