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Summary of Laboratory Experiments on Mating Disruption
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Effect of pheromone on male behaviour
Experiment 1 evaluated the mating success of females in the presence or absence of
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pheromone or pheromone analogues in Erlenmeyer flasks maintained in laboratory conditions,
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using 10 males and 10 females per flask (Schmidt et al. 1980). Hercon hollow fibers were used
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as a pheromone release device, at a rate of ca. 25 ng / h / fibre. The presence of pheromone
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suppressed mating of females, and the level of suppression increased with the concentration of
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pheromone for a range of 100 g to l mg AI or 125 ng / h to 1 g / h. Both components of the
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spruce budworm pheromone blend, E-11 tetradecenal and Z-11 tetradecenal, were as effective
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when tested alone as the natural blend (95:5 E:Z-11 tetradecenal), a finding that is somewhat
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surprising considering that neither component alone is attractive to males. Of different
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pheromone analogs tested, the only one as effective as the natural sex pheromone in suppressing
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mating was 10-(Cyclopent-1-en-1-yl)-decanal.
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Experiment 2 was conducted in a wind tunnel with two calling females at the upwind end
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of the tunnel (Sanders 1982). The wind tunnel was either left untreated (control) or treated with
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pheromone at a range of 10 to 10 000 pg / m3; for each pheromone concentration, two modes of
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pheromone release were used, uniform permeation of the wind tunnel or nine discrete plumes
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uniformly spaced in the tunnel. The males were enclosed for 3 h in the wind tunnel, and the
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number of individuals wing fanning or flying to the calling female was recorded for all
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treatments. The level of response of males declined with the concentration of pheromone, and
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the orientation toward pheromone sources was particularly suppressed when the pheromone was
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released from discrete plumes rather than uniformly in the atmosphere – with the exception of
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the highest concentration of pheromone. These results suggest that, at least for concentrations of
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pheromones that can be realistically achieved in the field, competition of synthetic pheromone
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sources with calling females is more likely to underlie mating disruption than camouflage of
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calling females by synthetic pheromone, and the release of pheromone from a few high release
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sites than from numerous low release sites may improve the efficacy of mating disruption.
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Experiment 3 was conducted in a wind tunnel and used different amounts of pheromone
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placed at the upwind end of the tunnel (PVC pellets with 0.0003 to 0.03 % AI on a wt / wt basis),
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corresponding to release rate of 0.1, 1 and 10 ng / h (Sanders 1985). One-day old males were
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either pre-exposed or not (experienced or naive moths, respectively) to the pheromone for a
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period of 3 h. The proportion of males that responded by wing-fanning or by orienting toward
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the pheromone sources was recorded. The lack of difference among naïve and experienced
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males in terms of orientation toward the pheromone source, even at the highest dose, suggests
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that sensory habituation is not the predominant mechanism underlying mating disruption.
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Experiment 4 was conducted in 3 L mating chambers maintained in laboratory conditions
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(Ponder et al. 1986). Mating of females was suppressed by the presence of pheromone, and the
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level of suppression increased with the concentration of pheromone from 1 to 320 g, although
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an average of 20% females were mated even at the highest concentration. In untreated cages, the
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mating probability of females increased with the ratio of males per female for a range of 1:1 to
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1.5:1, whereas the density of females had a relatively minor effect on female mating success for
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a range of 6 to 18 females. In pheromone-treated cages, in contrast, the mating success of
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females increased significantly with density. As expected, the proportion of mated females
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increased with the duration of the experiment from 20 to 68 h in both control and treated cages.
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Two analogs of the spruce budworm pheromone, 11,13-tetradecadienal and 12-tetradecenal (1:1
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E:Z ratio), were perceived by the male antenna and reduced captures of moths in traps when
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added to the sex pheromone, but only the first one suppressed mating of females.
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Experiment 5 was conducted in a flight tunnel with an array of 35 rubber septa
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impregnated with pheromone or pheromone analogs (E-11-tetradecenyl acetate or E-11-
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tetradecenol) (Sanders 1995). Two calling females were placed at the upwind end of the tunnel,
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and one male released at the other end. The analogs had no significant effect on the response of
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males for a dose of 10 g per septa, either in terms of wing-fanning or orientation toward
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females. Comparing different ratios of E:Z-11 tetradecenal (95:5, 80:20, and 50:50) and
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pheromone doses (0.1 and 1 g per septa) revealed that orientation of males toward females was
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most suppressed at the highest dose of the 95:5 ratio. Most males flew toward the pheromone-
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impregnated septa, which suggests false trail following as a mechanism of mating disruption; no
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evidence of sensory fatigue or habituation was detected. It was concluded that mating disruption
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may not suppress mating to near zero level, because a vast majority of males eventually reached
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the calling females when they were kept in the wind tunnel for a period of 3 h.
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Experiment 6 was conducted in a flight tunnel with 16 rubber septa baited with
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pheromone and pinned equidistantly on the top part of the tunnel, using concentrations of
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pheromone that ranged from 1 to 1 000 g per septa (Sanders 1996). Two one-day old females
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were placed at the upwind end of the tunnel. Males were kept in cages in the upper and lower
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section of the tunnel for 3 h before the onset of the experiment (experienced and naïve males,
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respectively), and their response recorded (wing-fanning, orientation toward calling females)
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over a four day period. Most naïve males wing-fanned independently of the pheromone
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concentration, whereas the incidence of wing-fanning declined with concentration for
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experienced males. The proportion of males that reached calling females declined with the
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concentration of ambient pheromone; the response of naïve and experienced males was similar,
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and no daily variation in response was observed during the course of the four day experiment.
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However, experienced males were slower in initiating flight and took significantly longer to
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reach calling females, especially as they got older. At release rates characteristic of female
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emission rate i.e., 10 to 100 g loadings, males were commonly attracted by the rubber septa,
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indicative of competitive attraction of pheromone sources with calling females. Sensory fatigue,
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indicated by a lack of upwind flight toward calling females or pheromone sources, occurred for
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loadings of 1 000 g in rubber septa, which corresponds to approximately ten times the natural
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release rate of females. Altogether, the results suggest that continuous exposure to around 20 ng
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/ m3 is necessary to achieve effective mating disruption in the field.
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Experiment 7 was conducted in a flight tunnel with a movable patterned ceiling that served
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to sustain the flight of males over prolonged periods (Sanders 1998). Two virgin females were
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placed at the upwind end of the wind tunnel before a male was introduced at the opposite end of
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the tunnel. All males reached the females in the absence of pheromone in the tunnel, whereas
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the orientation of males toward females declined with the concentration of pheromone (septa
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loaded with 0.1 to 100 g of AI). Some males flew for long durations (up to 53 min) toward
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calling females when the atmosphere was permeated with pheromone, which suggests that
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complete mating disruption will be difficult to achieve in the field because some males are likely
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to eventually locate a calling female.
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Effects of pheromone on female behaviour
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Experiment 8 was conducted using three day old virgin females maintained in Erlenmeyer flasks
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with an airflow consisting of either pheromone-impregnated air or “clean” air (Palaniswamy and
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Seabrook 1978). The presence of pheromone significantly increased the rate of walking,
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antennal grooming, extension of the ovipositor, and oviposition. Electroantennograms revealed
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that females perceived their conspecific pheromone at an amplitude of approximately two-thirds
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that of males.
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Experiment 9 reported a physiological response of females to their pheromone using the
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electroantennogram response technique (Palaniswamy et al. 1979). The response of females
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increased with age and was suppressed by a juvenile hormone analog.
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Experiment 10 was conducted in Erlenmeyer flasks containing females that were
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subjected to an air flow with or without sex pheromone; the pheromone was released from
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cartridges with 20 l of pheromone and replaced every 30 min (Palaniswamy and Seabrook
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1985). Exposure to the pheromone resulted in a larger number of females actively releasing
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pheromone (calling) and an earlier onset of calling. In other experiments, however, no effect of
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either pheromone or conspecific calling females on the calling behaviour was detected (Sanders
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and Lucuik 1972; Sanders 1995)
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Experiment 11 evaluated the response of females enclosed in 27 L screen cages with one
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shoot of balsam fir; the cages were treated with 14 pheromone dispensers pinned on the outer
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surface of the cage (corresponding to a release rate of 100 to 200 ng / h), or left untreated
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(Sanders 1987). The flight activity of females was recorded for a three day period using an
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electrostatic charges amplifier. The incidence of flight was significantly increased by the
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presence of pheromone for both mated and virgin females, and for some days the amplitude of
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difference was greater than ten. Virgin females remained inactive for two days following
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emergence, even in the presence of pheromone.
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Summary of Field Experiments on Mating Disruption
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Trials based on pheromone applied from the ground
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Experiment 1 was conducted in 1975 north of Sault St.-Marie, ON, in a stand of spruce
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and fir infested with a moderate density of spruce budworm (Sanders 1976). The experimental
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design consisted of a grid of nine traps (3 x 3) baited with virgin females in 40 x 40 m plots.
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Eight equidistantly spaced PVC lures releasing an unspecified amount of pheromone were placed
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between the traps. The number of males captured per trap was recorded one day before and after
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pheromone application, and the experiment was replicated six times in space and time. Female-
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baited traps captured an average of about 50 males per night before treatment. On the night of
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treatment, trap catches were reduced by 60% and 97% at the periphery and centre of plots,
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respectively.
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Experiment 2 was conducted in 1978 near St-Quentin, NB, in a mature stand of balsam
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fir – spruce (Schmidt and Seabrook 1979). The experimental design consisted of 16 square
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meter circular plots with cylindrical cages (61 cm diameter x 61 cm high) placed at the centre
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and surrounded by eight sources of pheromone positioned on tree stumps. Adult moths were
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confined in the cages at different densities and sex-ratios for 5 days, after which the females
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were dissected to determine their mating status. In control plots, the mating success of females
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was independent of the density of adults and increased with the relative abundance of males. For
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a release rate of 1 800 mg / ha / h, the mating success of females in treated plots was low (4%) at
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densities of one or three mating pairs (four of 89 mated females) and intermediate (23-27%) at a
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density of ten mating pairs per cage (24 of 89 mated females for a sex-ratio of one male per
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female; 11 of 47 mated females for a sex-ratio of three males per female). The mating success of
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females was similar for release rates of 330 and 1 800 mg AI / ha / h.
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Experiment 3 was conducted in 1981 near Fredericton in New Brunswick (Palaniswamy
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et al. 1982). The experimental design included 20 treated sites and four control sites; the
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distance between treated sites was > 500 m, whereas treated and control sites were > 3 km apart.
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Each plot consisted of a 12 m diameter shaded clearing surrounded by conifers. Four cylindrical
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screen cages (61 cm diameter x 61 cm high) were deployed at the center of each plot. Adult
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moths were confined in the cages at different densities and sex-ratios for 5 days, after which
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period the females were dissected to determine their mating status. In control plots, the mating
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success of females was independent of the density of mating pairs or sex ratio, and 228 of 566
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(41%) of females mated during the 5 day experiment. Mating success of females in pheromone-
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treated plots was extremely low (1.5%) at a low density of adults (one mated female among 67
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females in cages with three males and three females), low (8.9%) at intermediate density (22
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mated females among 250 females in cages with six males and six females), intermediate
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(14.1%) at high density (24 mated females among 170 females in cages with 12 males and 12
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females), and relatively high (20.7%) when the sex-ratio was male-biased (149 mated females
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among 720 females in cages with 12 males and six females). The level of mating suppression
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increased linearly with the release rate of pheromone for a range of 8 to 84 mg AI / ha / h.
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Experiment 4 was conducted in 1981 near Fredericton, NB, in a 10 ha mixed stand of
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balsam fir and white spruce with a density of ca. 0.3 late instars per terminal shoot (Alford and
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Silk 1983). Eight 10 x 10 m plots were established, with a distance between plots > 25 m. Two
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hundred Hercon flakes impregnated with pheromone were applied by hand in six plots (10 mg
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AI / ha / h) and the two remaining plots served as control. The effect of mating disruption on
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mating success was assessed using 480 females tethered near the tip of a branch. Mating success
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of females was higher in control plots than in pheromone-treated plots (62 vs 21%).
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Experiment 5 was conducted in 1982 near Durham, NB, in a 100 ha mixed stand of
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balsam fir and white spruce with a density of ca 0.5 late instars per terminal shoot (Alford and
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Silk 1983). Sixteen 20 x 25 m plots were established, with a distance between plots > 50 m.
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Two thousand Hercon flakes impregnated with pheromone were applied by hand in 12 plots (21
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mg / ha / h) and the four remaining plots served as control. The effect of mating disruption on
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female mating success was evaluated using sticky traps baited with virgin females (four traps per
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plot) and recording the number of males captured in each trap daily. The pheromone treatment
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reduced trap catches by about 80%, although the effect was minimal during the peak period of
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adult emergence. The level of disruption was higher when pheromone sources were clumped
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rather than uniformly distributed.
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Experiment 6 was conducted in 1989 near Noonan, NB, in two 1 ha sites composed of
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balsam fir and spruce (Kipp et al. 1990). One site was treated with 110 g AI / ha of pheromone
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and the other site left untreated. The effect of mating disruption on male orientation was
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evaluated using traps baited with virgin females or synthetic pheromones. Several males were
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captured in traps located in the control plot but none in the treated plot.
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Trials based on pheromone applied from the air
Experiment 7 was conducted in 1977 near Sault St.-Marie, ON, in two 12 ha white spruce
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stands heavily infested with budworms (20 to 25 third to fifth instars per 45 cm branch tips); the
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two stands were located 1.6 km apart (Sanders 1976). The control stand was treated with
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insecticide when larvae were in the sixth instar, but the mortality attributable to the insecticide
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was only 30%. The other stand was treated with pheromone applied from the air at a rate of 7.4
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g AI / ha in the middle of the flight season. Twenty traps baited with one virgin female per trap
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were deployed in each plot, and the females were replaced every second to fifth day. Following
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the application of the pheromone, the captures of males declined by > 90% from more than 80
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males per trap per night to less than five; captures of males in control plots remained consistently
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high (> 40 males per trap per night) over time. The effect of pheromone treatment was sustained
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for a period exceeding 10 days. The relatively high captures of males in female baited traps on
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the windward side of the pheromone-treated plot suggest that mating disruption is most effective
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in large stands with a low periphery to area ratio.
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Experiment 8 was conducted in 1977 in Ontario at two sites, one located near
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Searchmont and the other near Black Sturgeon Lake (Sanders 1979). The density of budworms
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was considerably higher at Searchmont (32 late instars per 45 cm branch tip) than Black
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Sturgeon Lake (< 1 late instar per branch tip). In Searchmont, a 250 ha white spruce stand was
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treated from the air with 10 g AI / ha of pheromone-treated Conrel hollow fibers applied from
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the air; a slightly larger stand 1.5 km to the west of the treated area served as a control. In Black
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Sturgeon Lake, two 10 ha stands located 1 km apart were treated with either 3 or 30 g AI / ha of
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pheromone, and one control plot was established > 10 km from the treated areas. In order to
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minimize the effect of female dispersal on the assessment of mating disruption in treated plots at
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Black Sturgeon Lake, all the estimates were obtained in 300 x 300 m plots surrounded by a 100
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m buffer area. The effect of mating disruption on the orientation of males toward pheromone
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sources was evaluated in each plot using > 25 traps baited with either synthetic pheromone or
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virgin females. At both locations, the density of males captured in pheromone- or female-baited
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traps was > 97% lower in treated plots than in control plants. The effect of mating disruption on
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female mating success was evaluated in each plot using 10 traps baited with virgin females for
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one day; the traps were replaced periodically depending upon the availability of females. In the
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control plots, the proportion of females that attracted males for mating was higher at the site with
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a high budworm density (Searchmont: 32 of 67 females, or 47.8%) than at the site with a low
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density (Black Sturgeon Lake: 12 of 65 females, or 18.5%). Mating disruption greatly reduced
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the mating success of females at the two locations: in total, only three of 127 females (2.4%)
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attracted males in pheromone-treated plots. The effect of mating disruption on the abundance of
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eggs could not be rigorously assessed at Black Sturgeon Lake due to the very low population
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density. In Searchmont, the number of egg masses did not significantly differ in control and
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treated plots, whereas the number of overwintering larvae was about 50 % lower in pheromone-
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treated plots than in control plots (26 vs 39 larvae per 10 m2 of foliage).
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Experiment 9 was conducted in 1978 near Saint-Quentin, NB, and near Amherst, NS, in
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mixed stands of fir and spruce (Miller 1979). The experimental design consisted of five 100 ha
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plots that were treated with 0, 0.1, 1.0, 10, and 20 mg AI / ha / h (New Brunswick) and 0, 0.1, 1,
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10, and 13 mg AI / ha / h (Nova Scotia). The pheromone was applied from the air using
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Conrel® hollow fibers footnote 2. We follow herein the recommendations of the authors and
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discard results in plots with 0.1 or 1 mg AI / ha / h, because the effect of the pheromone was
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minimal and inconsistent at these concentrations. The number of adults emerging in the
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experimental plots was similar in pheromone treated plots and control plots (New Brunswick: 58
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and 83 pupae pupae per 10 m2 of foliage; Nova Scotia; 226 vs 103). The effect of mating
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disruption on the orientation of males toward pheromone sources was evaluated using 15-40
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sticky traps baited with synthetic pheromone per plot. For traps placed at the mid-crown level
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(1.5 m above ground), the pheromone reduced male captures in traps by > 94 % in New
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Brunswick (70 vs 1226 males captured in 10 traps over 22 nights) and Nova Scotia (477 vs 10
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731 males). The pheromone also reduced captures of males in traps located in the upper canopy
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but the effect was slightly lower than that observed in the mid-crown (New Brunswick, 1 164 vs
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6 390 males; Nova Scotia, 3 620 vs 25 623 males). The latter result was attributed by the authors
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to a low level of mating disruption in the upper canopy toward the end of the flight season. The
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effect of mating disruption on female mating success was assessed using a variety of methods:
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(1) Laboratory-reared spruce budworms were confined in cylindrical screen cages (61 cm
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diameter x 61 cm high) at different densities of mating pairs (1, 3, and 10). The pheromone
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treatment reduced the proportion of mated females from about 73 to 40% early in the emergence
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season, but the reduction was weaker late in the season. The mating success of females
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increased with the density of mating pairs in the cage in the pheromone-treated plots, but was not
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affected by density in the control plots. (2) Females that had been collected in the field as pupae
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were tethered on branches in the mid-crown and upper canopy of balsam fir for a period of 24 h.
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A total of 166 tethered females were recovered from plots treated with > 10 mg AI / ha / h, 54 of
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which were mated (32.5%). For the females tethered in the mid-crown of trees, the proportion of
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mated females was lower in the plots treated with pheromone (six of 77, or 7.8%) than in the
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control plots (26 of 42, or 61.9%). Females tethered in the upper tree canopy experienced a
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relatively high mating success (22 of 47 mated females, or 46.8%). (3) Feral females were
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collected from trees sprayed with pyrethrin in all plots, with the exception of control plots. The
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low proportion of virgin females in plots treated with a low (< 1 mg AI / ha / h) concentration of
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pheromone (45 of 859 virgins, or 5.2%) compared with plots with a high (> 10 mg AI / ha / h)
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concentration of pheromone (139 of 972 females, or 14.3%) suggests some level of mating
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disruption among feral females. (4) Females that died from natural causes were collected in
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trays placed at the bottom of trees to determine their mating status. No virgin females were
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collected in a sample that included > 1 000 females. (5) In plots treated with a high
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concentration of pheromone, only two of 831 females collected in Malaise traps were virgin.
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The number of egg masses was slightly higher in pheromone-treated plots than in control plots in
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New Brunswick, whereas the opposite trend was observed in Nova Scotia.
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Experiment 10 was conducted in 1980 near Machias, ME, in mixed spruce-fir stands.
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The experiment included blocks of varying size (9 to 145 ha), two of which served as control and
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the remaining three were treated with pheromone applied from the air in Hercon flakes at
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different concentrations (50, 100, 500 g AI / ha) (Dimond et al. 1984). The density of spruce
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budworm was not reported, but the experiment was conducted at the peak of an outbreak. The
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effect of mating disruption on the orientation of males toward pheromone sources was evaluated
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using 20 sticky traps baited with synthetic pheromone and five unbaited traps per plot; due to the
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high density of budworms, the traps saturated with moths very quickly, thus the observations
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were conducted over 2 or 3 h periods. Captures of males exceeded 20 individuals per hour for
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several days over a 20 day interval in July. The reduction of male captures in pheromone-treated
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plots relative to control plots was more obvious at the high pheromone concentration (500 g AI /
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ha: >95 % reduction) than at the low pheromone concentrations (< 50 g AI / ha: ca. 50%
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reduction). The effect of mating disruption on female mating success was assessed using two
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approaches. (1) Virgin females were tethered on the upper tree canopy and their mating status
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recorded later. Sample sizes were low overall, but a trend suggested that mating disruption
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reduced female mating success early but not late in the season. (2) Feral females were collected
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either using Malaise traps suspended between the tree crowns or a gasoline powered vacuum
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device. The mating success of females was very similar in pheromone-treated and control traps,
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independent of the sampling device. The authors reported a high proportion of feral females
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were virgin (up to 55% in some plots) through the entire period of adult emergence, but provided
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no actual data. The relatively high incidence of virgin females was not due to a shortage of
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males per se because the ratio of males per female exceeded 10:1 at most sites. Counts of egg
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masses on the foliage failed to reveal any effect of mating disruption on either the abundance of
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egg masses or the fertility of eggs.
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Experiment 11 was conducted in 1981 near Thessalon, ON, in white spruce stands
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(Sanders and Silk 1981). The experiment included one 7.5 ha control plot and one 30 ha plot
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treated with 100 g AI / ha applied as Hercon laminated flakes from the air, with a distance of 10
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km between plots. The density of budworm was moderate (ca 0.3 emerged pupae per 45 cm
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branch section). The effect of pheromone treatment on male orientation was evaluated using 20
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synthetic pheromone baited traps in each plot, half of which were suspended in the tree canopy
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and the other half two m above ground. The traps in the control plots became saturated with
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moths during the peak period of flight (> 50 males per day), but the data clearly indicated lower
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captures of males in pheromone treated plots than in control plots; the reduction in trap catches
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appeared to be more pronounced for traps located near the ground than those in the tree canopy.
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The effect of mating disruption on mating success was evaluated by confining laboratory-reared
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moths in 1 m3 screen cages hauled into the canopy about 8m above ground, using six cages per
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plot; the experiment was repeated over time. The proportion of mated females was lower in
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pheromone-treated plots (102 of 222, or 45.9%) than in control plots (173 of 218, or 79.4%).
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However, all 18 feral females captured by net in the upper crown of spruce in pheromone-treated
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plots were mated, and the density of egg masses was not different in control and pheromone-
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treated plots (0.75 and 0.78 masses per 45 cm branch section).
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Experiment 12 was conducted in 1983 in Ontario using two large screen cages (9.4 x 5.6
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x 3 m) erected around live balsam fir trees at the centre of 3 ha plots, before the application of
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pheromone treatment (Seabrook and Kipp 1986). One plot was treated by air with Hercon flakes
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impregnated with pheromone (148 g AI / ha) and the other left untreated. A total of 2 300 moths
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(1 450 males: 850 virgin females) were confined in each cage for a period of 4 days. A reduction
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in mating success of 30-75% in the pheromone-treated plot relative to the control plot was
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reported.
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Experiment 13 was conducted in 1985 using the same protocol as in experiment 10. The
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body size (wing length) of mated and unmated females was assessed upon completion of the
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experiment (Kipp et al. 1987). The proportion of mated females was two times higher in the
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control plot (326 of 517 females, or 63.1%) than in the treated plot (147 of 458, or 32.1%).
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Mated females were larger than unmated females in the treated plot but not in the control plot.
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Experiment 14 was conducted in 1987 near Dunphy, NB, in a 25 ha plot treated with
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pheromone applied from the air as ICI Microcaps at a concentration of 96 g AI / ha, and in two
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control plots of unspecified area (Seabrook and Baskerville 1988). The density of spruce
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budworm at the onset of the experiment was lower in the treated plot than in the control plots
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(ca. 4.5 vs 9.0 empty pupal cases per m2 of foliage). The effect of mating disruption on male
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orientation was assessed using traps baited with synthetic pheromone or left unbaited (three traps
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per plot for each treatment); the traps were replaced periodically to prevent trap saturation. The
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data reported below are in terms of males per trap per day. The pheromone-baited traps captured
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> 10 times more males in the control plots than in the treated plot early in the emergence season
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until the 7 July (9.2 vs. 0.8); few males were captured in blank traps in either the control or
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treated plots (0.6 vs. 0.1). The level of mating disruption declined thereafter (17.1 vs. 3.5 in
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control and treated plots), which was attributed by the authors to a heavy rainfall “washing off”
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the pheromone from the foliage. Surprisingly, the blank traps captured a relatively high number
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of males, especially in control plots (2.5 vs 0.5). The effect of pheromone treatment on female
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mating success was assessed using adults collected in Malaise traps deployed on scaffold towers
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(six traps per plot). All the sampled females were mated. The results were difficult to interpret
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because only eight adults were captured in treated plots compared with 1 289 in the control plots;
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the authors noted that the traps may not have been deployed properly in treated plots. The ratio
329
of egg mass per pupal case was three times higher in the control plots than in the treated plot, but
330
data on the number of egg masses in different plots were not reported. It was concluded that the
331
data were difficult to interpret due to the variation in adult densities between plots and the
332
potential adverse effect of rainfall on mating disruption.
333
Experiment 15 was conducted in 1988 near Bathurst, NB, in three 25 ha stands
334
comprising > 40% of mature balsam fir (Seabrook 1989). Two plots were treated with
335
pheromone (20 and 90 g AI / ha) and the other plot was left untreated. Sampling was conducted
336
in the 10 ha at the center of each plot; the distance between plots was > 5 km. The study is
337
unique in that the mating status of males was recorded in the first half of the emergence period
338
(before ca 50% of females had emerged) using the method developed by Bergh et al. (1988); no
339
difference was observed in control plots (69 of 425 mated males, or 16.2%) and treated plots (58
340
of 423, or 13.7%). The effect of mating disruption on male orientation was assessed using traps
341
baited with synthetic pheromone or virgin females, or left unbaited. The high density of spruce
342
budworm resulted in very high captures of males (>800 individuals per trap for some days) thus
343
the traps in control plots rapidly became saturated with moths; data compiled during one day by
344
replacing the traps every two h indicated a high level of mating disruption (captures of males in
15
16
345
traps baited with pheromone and females in control plots: 835 and 260; in treated plots: 80 and
346
62); captures of males were high even in blank traps (average of 37 males per trap per day).
347
Female mating success was not assessed. The ratio of egg mass per pupal case was similar in
348
control and treated plots and reached a plateau above 3.5 late in the season.
349
Experiment 16 was conducted in 1996 near Fredericton, NB, in two plots, one of which
350
was 1.9 ha in size and treated twice during the season with pheromone applied in 3M microcaps
351
at a concentration of 100 g AI / ha; the second plot was left untreated (Lonergan et al. 1997).
352
The effect of pheromone treatment on female mating success was assessed by confining adults in
353
large screen cages (five to 15 mating pairs in 1 980 L cages), intermediate-sized screen cages
354
(two to three mating pairs in 7.8 L cages) and small screen cages (1 mating pair in Petri dish
355
sized cages); the experiment was repeated for each cage design over time. The difference in the
356
proportion of mated females between control and treated cages was higher early rather than late
357
in the season (Before 25 August in treated plots, 53 of 727 mated females, or 7.35%; in control
358
plots, 645 of 648 mated females, or 99.5%. After 25 August in treated plots, 61 of 168 mated
359
females, or 36.3%; in control plots, 158 of 160 mated females or 98.8%). No apparent effect of
360
cage size on mating success was detected.
361
Experiment 17 was conducted in 2000 near Fredericton, NB, in two plots, one of which
362
was 4 ha in size and treated with 50 g AI / ha of pheromone in 3M microcaps, and the other left
363
untreated (Silk and Kettela 2001). The effect of mating disruption on female mating success
364
was assessed by confining two mating pairs in 7.8 L screen cages; the experiment was repeated
365
several times during the season both low in the canopy and in the upper crown. The proportion
366
of mated females was considerably lower in treated plots (12 of 122 mated females, or 9.8%)
16
17
367
than in control plots (90 of 116 mated females, or 77.6%). The level of mating suppression was
368
more pronounced early in the season, but no apparent effect of canopy height was detected.
369
Experiment 18 was conducted in 2001 near Fredericton, NB, in three plots, two of which
370
were 5 ha in size and treated with either 25 or 75 g AI / ha of pheromone applied from the air in
371
3M microcaps; a control 1 ha plot was left untreated (Silk and Kettela 2002). The effect of
372
pheromone treatment on female mating success was assessed by confining two mating pairs in
373
17.5 L screen cages; the experiment included 12 cages per plot and was repeated over time. The
374
mating success of females was low in the high pheromone dose plot (15 of 165 mated females, or
375
9.1%), intermediate in the low pheromone dose plot (36 of 165 mated females, or 21.8%), and
376
high in the control plot (105 of 145 mated females, or 72.4%).
377
Experiment 19 was conducted in 2004 in Balsam Lake Provincial Park in southern
378
Ontario in three white spruce stands, two of which were treated with pheromone at a
379
concentration of 20 g AI per ha (20 ha plot) and 50 g AI / ha (46 ha plot); a third plot located 1
380
km away from the treated plots was left untreated and served as a control (Kettela and Silk
381
2005). The density of spruce budworm at the onset of the experiment averaged 4.8 late instars
382
per 50 cm branch section. The effect of pheromone treatment on male orientation was assessed
383
using traps baited with synthetic pheromone (30 traps per plot); the traps were checked daily.
384
The number of moths per trap was consistently lower every day through the emergence season in
385
the plot treated with 50 g AI / ha than in the control plot. Male captures were also reduced in the
386
plot treated with 15 g AI / ha, yet to a considerably lesser extent than for the high dose treatment.
387
The effect of mating disruption on female mating success was assessed in ten L screen cages
388
with two males and one virgin female; 18 cages were deployed in each plot and the adults
389
replaced every third day. The proportion of mated females was low at the high pheromone dose
17
18
390
(6%), intermediate at the low pheromone dose (48%), and high in the control plot (82%). The
391
mating success of wild females was also determined for individuals captured with a sweep net.
392
All the females collected in the control plots after the 23 June were mated; in contrast, the
393
proportion of mated females varied between days from 30 to 80% at the high pheromone dose,
394
and from 55 to 85% at the low pheromone dose. The density of egg masses remainded
395
consistently low at the high pheromone dose (1.16 to 1.32 masses per 50 cm branch section) and
396
steadily increased over time at the low pheromone dose (3.98 to 13.20 egg masses per 50 cm
397
branch section between 23 June and 11 July); the data expressed in relative terms (egg masses
398
per pupal case) was 0.22 for the control plot, 0.18 for the low pheromone concentration, and 0.12
399
for the high pheromone concentration.
400
Experiment 20 was conducted in 2005 near Craighurst, ON, in two white spruce stands,
401
one of which was 8.2 ha in area and treated with 50 g AI / ha of pheromone; the other plot was
402
25 ha in area and served as a control (Kettela et al. 2006). The density of pupa at the onset of
403
the experiment was approximately 1.7 individuals per 50 cm branch section. The effect of
404
mating disruption on male orientation was assessed using Multipher traps baited with synthetic
405
pheromone and replaced at intervals of 3-6 days (15 traps in control plots and 30 traps in treated
406
plots). The average number of males per trap was 85% lower in treated plots (2.2) than in
407
control plots (14.8). The effect of pheromone treatment on female mating success was assessed
408
using 10 L screen cages with two males and one female placed in the field for a period of three
409
days. The proportion of mated females was considerably lower in the treated plot (37 of 98
410
mated, or 37.8%) than in control plots (97 of 105 mated females, or 92.3%). A total of 26 feral
411
free-flying females were captured, all of which were mated; the authors did not specify if these
412
females were captured in the treated or control plots. The number of egg masses sampled on the
18
19
413
foliage was considerably lower in the treated plot than in the control plot (five and 38 egg masses
414
in total, respectively).
415
Experiment 21 was conducted in 2008 on the North Shore in Québec in a stand with >
416
40% of fir infested with budworms (20 to 25 overwintering larvae per branch) (Trudel et al.
417
2009). The strength of the study was the replicated structure of the experiment (factorial design
418
including all combinations of Bt and/or pheromone application at a dose of 35 g AI / ha,
419
corresponding to four treatments repeated four times each, for a total of 16 50 ha blocks). The
420
distance between experimental blocks was not specified by the authors. The interpretation of the
421
results is difficult because the application of Bt before adult emergence had no effect on any of
422
the demographic parameters reported in the study. The captures of males in traps baited with
423
synthetic pheromone were reduced by 80 to 99% in blocks treated with pheromone, and the
424
reduction was consistent over a 39 day period. Traps baited with virgin females were used as a
425
proxy to assess the mating success of females. Although the presence of pheromone reduced the
426
percentage of cages that captured at least one male and the overall number of males per trap, the
427
proportion of mated females within the cages was independent of the pheromone treatment. No
428
difference in reproduction by female budworms could be detected as a function of pheromone
429
treatment, either in terms of egg or larval densities.
430
431
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432
433
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434
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Bergh, J.C., Eveleigh, E.S., and Seabrook, W.D. 1988. The mating status of field-collected male
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Palaniswamy, P., and Seabrook, W.D. 1985. The alteration of calling behaviour by female
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Ponder, B.M., Kipp, L.R., Bergh, C., Lonergan, G.C., and Seabrook, W.D. 1986. Factors
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Sanders, C.J. 1976. Disruption of sex attraction in the Eastern spruce budworm. Environmental
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Sanders, C.J. 1996. Effects of prolonged exposure to different concentrations of synthetic
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526
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