Effect of Color on the Trapping Effectiveness of Red Palm Weevil Pheromone Traps
The Red Palm Weevil (RPW), Rhynchophorus ferrugineus Olivier (Curculionidae: Coleoptera), is the most serious and difficult to control insect pest on date palm (Phoenix dactylifera L.) in the United Arab Emirates. The aim of this study was to evaluate the effect of trap color on trap effectiveness in catching R. ferrugineus. Traps baited with the male aggregation pheromone of the red palm weevil were installed in four date palm farms in Abu Dhabi, United Arab Emirates, in 2007. Seven trap colors were tested for attraction to the red palm weevil (red, green, blue, orange, pink, yellow and white). The highest weevil catch was achieved in the red trap (p<0.05). Present results indicate that trap color has a significant effect on trap effectiveness, which suggests that dark-colored traps in general and the red in particular, catch more weevils. Therefore, the use of red traps will be more effective in the control programs of this economic pest.
The red palm weevil, Rhynchophorus ferrugineus Olivier (Curculionidae:
Coleoptera), is one of the most important insect pests attacking date palm trees
(Phoenix dactylifera L.) in the Arabian Gulf states. It is an invasive
pest, native to Pakistan, which was first recorded in the northern United Arab
Emirates (UAE) in 1985 and has since spread to almost the entire UAE (El-Ezaby
et al., 1998) and to Oman. In addition, this pest is currently spreading
in Mediterranean European countries and posing a threat to both date production
and the appearance of the landscape (Ferry and Gomez, 1998;
Khalid, 2007; Murphy and Briscoe,
1999). The high pest status of R. ferrugineus is attributed to its
presence throughout the whole year, the severe damage it causes to infested
trees and the difficulty of discovering early infestations. As an internal plant
borer, R. ferrugineus is difficult to detect in palms in the early
stages of an attack (Abrahamet al., 1998). Females
deposit eggs in concealed places on the tree and the resultant larvae bore inside
the tree trunk causing severe damage. Furthermore, Abraham
et al. (2002) reported that the pupa is protected by the thick and
strong cocoon and the adult weevil has a dense exoskeleton making control by
natural enemies difficult.
Several methods are used to control the red palm weevil. The most effective
and environmentally sound method is the food-baited pheromone trap (Abraham
et al., 1998; Faleiro et al., 1998).
These traps have been successfully used as mass trapping devices to manage the
red palm weevil on date palm in the Middle East. It has been reported that using
aggregation pheromone traps was very effective in catching the adults of the
red palm weevil and curtailing population growth in the field (Abraham
et al., 1999, 2000; Faleiro,
2000). Abraham et al. (1999) found that the
weevils captured by using pheromone traps were female dominated and the use
of the traps reduced insect numbers over time. Oehlschlager
et al. (1995) reported a 90% decrease in the numbers of the American
palm weevil (Rhynchophorus palmarum L.) captured in the oil palm plantations
after two years of pheromone trapping in Costa Rica. They also indicated that
the traps caught more females than males. Similar results were reported by other
scientists (Abraham et al., 1999; Faleiro
and Rangnekar, 2000; Vidhyasagar et al., 2000;
Al-Saoud, 2006, 2007). Catching female weevils is
desirable in any Integrated Pest Management (IPM) program because they are the
precursors of the damaging larval stages.
Traps of different designs and colors have been used to capture adults of R.
ferrugineus. Hallett et al. (1999) reported
a greater response of red palm weevil to black bucket traps than to white traps.
Similarly, Ajlan and Abdulsalam (2000) found that green
reusable bucket traps captured more red palm weevils compared to white and yellow
traps and Sansano et al. (2008) working in Spain
reported that brown-reddish traps were more effective than white traps.
The purpose of this study was to evaluate the effect of trap color on trap effectiveness in catching R. ferrugineus.
MATERIALS AND METHODS
The experiment was conducted at four date farms at Al-Rahba, Abu Dhabi (Lat.
24° 28' N; Long. 54° 22' E), UAE in 2007. Each farm contained at least
140 date palm trees of different ages (3-20 years).
Pheromone traps were fabricated using a 10 L polypropylene bucket with four
rectangular (3x8 cm) windows cut equidistantly below the upper rim of the bucket.
The distance between each window and the bottom of the bucket was 16 cm. The
bucket was covered with a lid that had three windows similar to the ones on
its sides. The upper surface of the lid had a small handle to ease opening the
trap and the lower side had a small knob on which a wire was fixed to hold the
pheromone and kairomone dispensers. The outer surface of the bucket was rough
with small projections (1-2 mm) to help the weevils cling to the trap and enter.
Each trap contained the following materials: (1) 300 g of dates, (2) dispenser
of the R. ferrugineus male aggregation pheromone containing 70 mg of
the active ingredient (4-Methyl-5-Nonanol (9 parts) + 4-Methyl-5- Nonanol (one
part)) at 95%, purity, (3) dispenser of the kairomone containing 40 mL of the
active ingredient Ethyl Acetate at 98% purity and (4) 5 L of water. The water
was always replenished to keep sufficient moisture in each trap. Food bait (dates)
was changed every two weeks. Based on the dispensing rates, the pheromone was
replaced every three weeks and the kairomone every month. The original color
of the bucket trap was white, which was changed by painting with commercial
acrylic paint sprays. Seven colors were tested: white, yellow, red, orange,
blue, pink and green. All paints were sourced from Al Muqarram Insulation Material
Industry LLC (Sharjah, UAE: www.muqarram.com).
Experimental Design and Trap Installation
The experimental design was a randomized complete block design with seven
treatments (colors) and four replicates (farms). A total of 28 traps were installed
for a trapping period from 1 February until 1 July 2007. This time period (5
months) was selected because it includes the part of season in which the adults
of R. ferrugineus are more active and reach their population peak. Large
beetle population in the field amplifies the effect of trap color on beetle
catch. In each farm, the traps were installed near the farm peripheries with
two rows of trees left as an outer border. The distance between traps was 50
m and each trap was 4 m away from date palm trees. Traps were buried in the
ground down to the level of side windows to facilitate entrance of R. ferrugineus.
Part-burying the trap also prevented it from being over-turned by wind or animals.
Captured weevils were collected weekly. In order to minimize the effect of trap
location on the number of captured insects, the position of each treatment was
re-randomized each week.
The data were subjected to ANOVA using the PROC GLM procedure and the means
were compared by carrying out the Least Significant Difference (LSD) procedure
of the SAS statistical package (SAS, 2001).
There were significant differences between trap colors in the number of captured
weevils (F = 10.83, df = 6, 18, p<0.001) (Fig. 1). During
the trapping period, the maximum number of R. ferrugineus per farm was
captured in the red traps (127.8), which was significantly different from blue
(t = -2.33, df = 18, p = 0.03), green (t = -3.45, df = 18, p = 0.003), Orange
(t = -5.07, df = 18, p<0.0001), pink (t = -5.54, df = 18, p<0.0001), yellow
(t = -5.74, df = 18, p<0.0001) and white (t = -6.63, df = 18, p<0.0001).
Blue and green traps ranked second (108.0 and 98.5, respectively) and no significant
differences occurred between them (t = -1.12, df = 18, p = 0.28).
||Mean±SEM number of adult R. ferrugineus captured
per pheromone trap per farm at Abu Dhabi, UAE, totaled over the period 1
February to 1 July 2007. Columns labeled with the same letter are not significantly
different (p>0.05, PROC GLM, LSD, SAS, 2001)
dynamics of adult R. ferrugineus captured per pheromone trap in
four farms at Abu Dhabi, UAE, totalled over the period 1 February to 1
They were followed by orange and pink traps (84.8 and 80.8, respectively) which
were also not significantly different (t = -0.47, df = 18, p = 0.64). Yellow
(79.0) and white (71.5) traps caught the least number of R. ferrugineus
and did not significantly differ from each other (t = -0.88, df = 18, p = 0.39).
It appeared that dark-colored traps captured more R. ferrugineus weevils
than the light-colored traps.
There was temporal variation in number of R. ferrugineus per trap per month during the trapping period (Fig. 2). Rhynchophorus ferrugineus population attained a peak in March for all trap colors. Red traps captured more R. ferrugineus weevils compared to the other trap colors in February, April, May and June (89,103, 70 and 91, respectively). The only exception was March in which blue traps collected slightly more weevils than red traps (152 and 148, respectively).
In the past ten years, mass trapping with pheromone-baited traps has been successfully
used to control R. ferrugineus in several countries, including the UAE.
Many phytophagous insects respond positively to light reflectance patterns of
their host plant and these responses can be quite specific (Prokopy
and Owens, 1983). Therefore, trap color plays a major role in the effectiveness
of mass trapping. Ajlan and Abdulasalam (2000) reported
that the green-colored traps captured more R. ferrugineus compared to
the white and yellow traps. Similarly, present results demonstrated that green
traps were more effective than white traps. However the red traps were most
effective, catching significantly more weevils compared to the other colors.
This finding is in agreement with that of (Sansano et
al., 2008) who also found that brown-reddish colored traps caught more
weevils compared to their white counterparts. This is important because the
R. ferrugineus mass-trapping program in the UAE recommends the use of
white traps. Also, most of the date palm growers use white and yellow traps.
Yet, in our study the red traps caught approximately 1.8 times as many weevils
as the white traps. The most plausible explanation is simply that R. ferrugineus
uses dark colors as visual cues to locate the date palm tree trunk and the trap.
The weevil responds more positively to dark objects and uses them in the visual
short-range host finding. Kirk (1984) postulated that
both Coleoptera and Lepidoptera with wood boring larvae are attracted to red,
brown and black, although mainly as a contrast with the background rather than
any specific visual cue. Temporal variation in numbers of R. ferrugineus
captured per trap per month for each of the seven colors may reflect seasonal
changes in temperature and other weather parameters. The population dynamics
showed that date palm growers in UAE should maintain the traps during the season
and particularly in March when the R. ferrugineus population reaches
its peak in order to capture the maximum number of insects.
In conclusion, present results demonstrated that red is a better trap color compared to white and yellow, which are currently used by UAE date palm growers. Although, more work could be done to fine-tune trap efficiency, in the meantime, the use of red traps would be a simple means to improve the effectiveness of the R. ferrugineus mass-trapping control programs.
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