Evaluation of ExosexTM SPTab, a new mating disruption dispenser against the Indian meal moth, Plodia interpunctella (Hübner), in a wooden house in central Japan
Hideakira TSUJI1)*, Kakuro KANNO2), Akiko TOJIMA2), and Junichiro KATAYAMA2)
1) KSK Institute for Environmental Biology, F-409, 2-1 Nishino-Rikyucho, Yamashina-ku, Kyoto 607-8345, Japan
2) Semco Co., Ltd., 26-5, 1-chome Kawanishi-cho, Takatsuki 569-1133, Japan
1)環境生物研究会 〒607-8345 京都市山科区西野離宮町2-1，F-409
2)環境機器株式会社 〒569-1133 高槻市川西町１丁目，26-5
The efficacy of a new mating disruption dispenser, ExosexTM SPTab, from which attracted male moths pick up tablet powder and female sex pheromone from the dispenser, forming mimic females and mobile dispensers, was evaluated against the Indian meal moth, Plodia interpunctella (Hübner), using two vacant neighboring rooms in a wooden house in central Japan. The number of male moths markedly increased in the treatment room in 10 trials and did not in 2 among the 12. The 2 trials were in April and May, when the activity of moths was very low even under the room conditions. These suggest that male moths were attracted to the pheromone dispenser from the outdoor environment in warmer months. The number of larvae produced in the oviposition trap was 86, 66, 61, and 33%, respectively, on each control (100%), in all the 4 trials where the larvae were found in the traps. The mean ranged from 61.5 ± 21.42 (p=0.05). The results suggest that SPTab may decrease the next-generation larval infestation, even if it may induce a temporary increase in male moths in the room.
Key words: Indian meal moth（ノシメマダラメイガ）, sex pheromone（性フェロモン）, mating disruption（交配攪乱）, SPTab dispenser（SPTab ディスペンサー）
Huang and Subramanyam (2002) experimentally showed that egg viability of the Indian meal moth, Plodia interpunctella (Hübner), decreased by 22%/day when female mating was delayed, and males with mating delayed for 5 days were unable to inseminate females. These results suggest that methods that can delay and disrupt mating may be effective behavioral strategies for managing this important pest of stored products.
In order to reduce or replace insecticide treatments, the mating disruption method has been successfully applied to some insect pests (Aono et al., 1989; Snow, 1990, Wakamura, 1992; Matsumoto et al., 2007; Carter and Fraser, 2009), as well as Plodia interpunctella (Ryne et al., 2001; Ryne et al., 2007, Burks, et al., 2011). The method uses large amounts of synthetic female sex pheromones to confuse male adults and limit their ability to locate calling female adults. As a result, mating is either delayed or prevented, and female adults lay fewer or no fertile eggs in their lifetime.
There are some limitations to disruption method programs. Active ingredients are usually not suitable for spraying or dusting formulations. When manually applied dispensers are used, the method needs so many dispensers to cover the wide target area as evenly as possible that no bunches in one area are allowed to save labor time and application cost. Such limitations make it difficult to apply the disruption method for controlling many species of insect pests including the Indian meal moth, Plodia interpunctella, one of the most hazardous species of stored product pest insects.
To overcome these limitations, a new technology system, ExostatTM SPTab, has been developed that delivers a carrier powder containing the female sex pheromone
(Z,E)-9, 12-Tetradecadienyl acetate, (ZETA), directly to the male cuticle. The proprietary carrier powder, EntostatTM (Exosect Ltd., Winchester, UK) is electrostatically chargeable and adheres to insect cuticles via electrostatic attraction (Armsworth et al., 2006, 2008; Nansen et al., 2007a; b). The expected behavior process of male Indian meal moths is as follows. 1) Male moths are attracted to the dispensers containing a compressed Entostat tablet, and become contaminated with Entostat containing ZETA (Baxter et al., 2008). 2) The male's sex pheromone receptors become overloaded, and so the male is unable to locate females. 3) A male carrying the powder forms a mobile pheromone dispenser, producing false pheromone trails, which attract additional males. 4) Contact between the males ensures that the powder and confusion effect (Auto-ConfusionTM) is automatically passed on, leading to effective mating disruption. 5) The Auto-Confusion effect markedly reduces the chances of the female moth mating reducing the number and viability of eggs. (Items with the TM mark are trademarks of Exosect Ltd.)
The authors have evaluated the effects of this system on the population of the Indian meal moth, using two rooms in a wooden house in a suburb of Kawaguchi, Saitama Prefecture (nearby Tokyo). The results obtained in 2010 and 2011 are reported here.
Materials and Method
1. Pheromone dispenser
The pheromone dispenser (SPTabTM) is a plastic hanger dispenser in which one compressed powder cylinder (tablet) is inserted (Fig. 1).
Fig. 1. The pheromone dispenser and it’s vertical section
T: Inserted tablet
The tablet contains the active ingredient 0.93%w/w Z.E-9,12 Tetradecadienyl acetate (10 mg/tablet), the female sex pheromone of Plodia interpunctella, formulated in a proprietary electrostatic wax powder (EntostatTM,) derived from the wax palm. The active ingredient which is impregnated into the powder is shared as a common female sex pheromone by several species of the family Pyralidae; Plodia interpunctella: Ephestia kuehhniella, E. cautella, and E. elutella.
2. Trial rooms
Two neighboring, southern and northern, vacant rooms of a similar size (5.4 × 3.6 m) on the second floor of a wooden house were used alternately as the treatment or the control room (Fig. 2).
Fig. 2 Arrangement in the test rooms
■：Pheromone dispenser ○：Release container □：Oviposition trap
A pheromone dispenser was placed in one room a‚“ a test, and the treated and untreated rooms were changed alternately for the subsequent tests.
The dispenser was affixed to the wall (or an exhaust hood over a kitchen range) at a height of 1.7 m. For release tests, containers that held male and female pupae were separately placed on the floor. Oviposition traps were placed on the floor to examine the effect on the next generation.
Each room had wooden flooring, and one exit door on the west side leading to the ground by an external staircase, but no direct staircase to the first floor in the house. There was a door between the two rooms. The doors and windows were closed during the trials except when making observations. There was a small toilet and sink in the northern room, but no furniture, and no other necessities of life including food, in both rooms. Air-conditioners and ventilation fans were not used during the trials.
Each time, one dispenser was affixed to a surface of the southern wall of the southern room or on the northern ventilation cover of the northern room at a height of 1.7 m (Fig. 2). Ventilation fans were not used during the trials.
3. Moth-release trials
As shown in Table 1, virgin moths were artificially released in the rooms in each of 3 trials among 12 (2 in 2010 and 1 in 2011), although it turned out later that this procedure was not necessary for obtaining the next-generation larvae except when no naturally occurring moths were expected outdoors in early spring. Actually the release cups were placed in the rooms just before adult emergence started.
To obtain the virgin moths, fully grown larvae were divided into 2 sex groups, which were allowed to pupate in several pieces of corrugated cardboard in different containers. Male larvae were determined by the testes that could be recognized through the surface skin. Then, the 2 sex containers were placed in each of the trial rooms just before moth emergence (Table 1). The actually released number of moths was estimated after the trial from the number of pupal skins following successful ecdysis in each container.
After the period of each trial, the number of moths in the room, dead or alive (most of them were dead), was counted to evaluate the influence of the dispenser on the number.
Table 1. Number of moths released and collected
4. Trials with naturally occurring moths
In 9 trials among 12 (2 in 2010, 7 in 2011), no virgin moths were released in the rooms. The number of moths in the rooms was also counted after the period of each trial.
5. Oviposition traps and the number of larvae produced
An oviposition trap was placed on the floor of each room in 10 trials (2 trials in 2010 and 8 in 2011) among the 12. A plastic container (100 x 100 mm square or 110-mm -diameter round) with 40 g of rice bran was placed as the trap on the floor of each room, just under the windowless wall opposite the wall or ventilation cover on which the dispenser was affixed.
After the trial, the oviposition traps were withdrawn and kept at a 25℃ or higher temperature in an incubator until the larvae grew into detectable sizes. Then, the traps were heated in a hot water bath, and the larvae coming out and dying on the surface of the rice bran were counted.
1. Relations between released and collected moths in the 3 release trials
The relations between the numbers of moths released and those collected in September of 2010 and April of 2011 are shown in Table 1 and Fig. 3. Most of those collected were found dead on the floor.
The results show that, in the treatment room, the numbers of collected male moths in 2 September trials were 5.4 to 6.6 times higher than those released in the same room, while being not so different from those released in the control room. In the April trial, however, the collected number was less than half of those released in both the control and treatment rooms.
Fig. 3. Ratios of collected to released moths
The number of collected female moths was always smaller or much smaller than those released in all 3 trials.
2. Number of moths collected in 9 trials with naturally occurring moths
Naturally occurring moths collected per day in 9 trials are shown in Table 2 and Fig. 4. In all trials, the collected number of males was greater or much greater than that of females, and no females were obtained in 6 trials among the 9.
Excluding the May 8-31 trial, the number of male moths collected in the treatment room was much higher than that in the control room
Table 2. Naturally occurring moths collected per day
Fig. 4. Naturally occurring moths collected per day
3. Number of larvae in the oviposition trap
Oviposition traps were used in 10 trials (2 among 4 in 2010, and all the 8 trials in 2011). However, a comparable number of larvae were obtained in only 4 (2 in 2010 and 2 in 2011).
The results of the 4 trials in which larvae were obtained in oviposition traps are shown in Table 3 and Fig. 5. In all 4 trials, the number of next-generation larvae produced in traps was smaller in the treatment room than in the control room. The % numbers of larvae in the treatment room (% of control) were 86, 66, 61, and 33%, respectively.
Table 3. Number of next-generation larvae in oviposition traps in 4 trials
95% confidence range
95% confidence range
Fig. 5. Number of next-generation larvae in release trials
Above: Numbers in 4 trials
Below: Numbers in the treated rooms (% of control)
No larvae were obtained in oviposition traps in other oviposition trials even when a greater number of male moths were obtained (Fig. 6)
Fig. 6. Number of next-generation larvae in 2011 trials
The data on the relations between the numbers of male moths released and those collected in the room (Table 1 and Fig. 3) indicate that outdoor male moths should have been attracted by the active ingredient in the dispenser in warmer months, although few or not enough moths had emerged outdoors in April and early May (Hirao, 1994).
The number of naturally occurring moths collected (Table 2 and Fig.4) also indicates the same tendency as described above. Very few or no active moths seemed to have invaded the rooms from the outdoor environment in early June as well as in April and May. No female moths, however, were found in the rooms even in July to September trials, when male moths were abundant.
In all 4 trials where the number of next-generation larvae could be compared, the % number was smaller in the treatment room than in the control room (Table 3 and Fig.5; Confidence range of the mean: 61.5 ± 21.4, P < 0.05). This may be because of the mating disruption effect due to the marked attraction of male moths to SPTab, as well as to auto-confusion caused by the increased number of male moths attracted to and touching the dispenser, and then acting as mobile pheromone dispensers or mimicking females.
No larvae were obtained in oviposition traps in and after the May 30 - June 20 trials in 2011 (Fig. 6). This may be partly because no or very few female moths could invade the room, even though many male moths could (Table 2 and Fig. 4). The reason is not clear, so the total effect of SPTab on female moths remains unknown.
If any female moths could oviposit and then exit, there may be some possibility that the high room temperature killed the eggs; the maximum temperature ranged from 38 to 42 ℃ when measured from August 10 through October 4, 2011. When examined in an incubator, a 48-hour exposure to a high temperature of 38℃ killed 100% of the eggs, and a 72-hour exposure killed 88.5% of the first instar larvae (Tsuji, unpublished data).
These results suggest that the introduction of these auto-confusion type pheromone dispensers inside a room may have the potential to reduce infestation by next-generation larvae in the room, even if it might increase the number of male moths especially just after the installation of the dispenser in warmer seasons.
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