32 5
MANAGEMENT OF THE RED PALM WEEVIL, RHYNCHOPHORUS
FERRUGINEUES OLIV., BY A PHEROMONE/FOOD-BASED
TRAPPING SYSTEM
Walid Kaakeh1, Fouad El-Ezaby2,
Mahmoud M. Aboul-Nour1, and Ahmed A. Khamis1
1Department of Plant Production, United Arab Emirates University
P. O. Box 17555, Al-Ain, U.A.E.
2Department of Agriculture and Livestock, Al-Ain, U.A.E.
ABSTRACT
Tests were conducted to determine the feasibility and the effect of
using pheromone/food-baited traps in a trapping system within a commercial
date palm plantation on the spatial dynamics of the red palm weevil
(Rhynchophorus ferrugineus Oliv.) (RPW). One registered pheromone lure
(Ferrolure+ or called pheromone 7 in the test) and four experimental
aggregation pheromone lures (called pheromone 5, 6, 8, and 9) were
evaluated in ten farms from 1998 to 2000. The effect of trapping on the
spatial patterns was based on the number of weevils caught per trap per
specific period. Efficacy of various pheromones used was determined based
on the number of weevils caught per trap per time period and the percentage
of tree infestations. There was a variation in trap catches of the pheromone
lures used during the growing seasons. Two major population peaks were
noticed: the first peak started early-March and ended mid-May; the second
peak started mid-September and ended late-December. The total number of
infested trees was significantly decreased compared with the previous years
where chemicals were used for the control of the weevil. The percentage
reduction of infestation was 90.4, 90.9, and 100% for the treatments of
pheromone lures 5, 8, and 7, respectively. The ability of the tested
pheromones to capture more females than males in the traps makes trapping a
potential tool for managing this economic insect. The release rate of the
pheromone lures influenced the efficacy of the pheromone in attracting the
adults. The results presented here are promising in utilizing pheromonesfood
baited traps for reducing RPW populations and protecting palm trees
from RPW infestations within the field. If large-scale tests are desired,
pheromones lures 5, 7, and 8 could be selected for further evaluation and/or
commercial use.
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Additional Index Words: Rhynchophorus ferrugineus, pheromone,
trapping, date palm trees
INTRODUCTION
The red palm weevil (RPW), Rhynchophorus ferrugineus Oliv.,
(RPW) (Curculionidae: Coleoptera), is an economically important, tissueboring
pest of date palm in many parts of the world. The insect was first
described in India as a serious pest of coconut palm (Lefroy, 1906) and later
on date palm (Madan Mohan Lal, 1917; Buxton, 1918). The weevil was
recorder later in Seri Lanka, Indonesia, Burma, Punjab, and Pakistan
(Laskshmanan, 1972). Currently, the insect is a major pest of date palm in
some of the Arabian Gulf States including Saudi Arabia, United Arab
Emirates, Sultanate of Oman, and Egypt (Cox, 1993; Abraham et al. 1998).
The agroclimatic conditions prevalent in this region and the unique
morphology of the crop, coupled with intensive modern date palm farming,
have offered the pest an ideal ecological habitat (Abraham et al., 1998).
Current strategies for management of R. ferrugineus infestations
involve monthly surveys of all palms in infested regions. Infested palms are
removed and infected parts are sectioned and buried. As a preventative
measure all palms in infested areas are sprayed to run off with a variety of
insecticides. Because of the environmental pollution and economic costs of
continuous insecticide spraying, more environmentally and economically
acceptable alternatives are being sought to aid in the management of this
pest.
The recent discovery of the male-produced aggregation pheromone
[ferrugineol, 4-methyl-5-nonanol] for R. ferrugineus (Hallett et al. 1993a, b)
made the implementation of pheromone-based monitoring and trapping of
this weevil possible for the management of this pest. Gunawardena and
Bandarage (1995a) found that at a release rate of 0.38 mg synthetic
ferrugineol/day from capillaries suspended in bucket traps filled with soap
water, significantly caught more weevils compared to a control trap in the
field They also found (1995b) that a combination of ferrugineol with 5
alcohols (n-propanol, n-butanol, n-pentanol, n-hexanol, and n-nonanol) were
field-tested as baits. A significantly higher catch of 0.85 weevils/day/trap,
was obtained with ferrugineol and n-pentanol. In a recent study, El-Garhy
(1996) reported that catch rates were highest during the period from April to
June (50-65 weevils), which corresponds to the warmer weather in Egypt.
El-Ezaby et al. (1998) reported maximum catches in March and April.
32 7
Aggregation pheromones have been reported as effective tools for
monitoring and trapping RPW in the field (Gunnawardena and Badarage,
1995a, b; El-Ezaby et al., 1998; El-Garhy, 1996). The objective of this study
was to determine the feasibility and the effect of using pheromone-food
baited traps in a pheromone trapping system within a commercial date palm
plantation, in the United Arab Emirates, on the spatial dynamics of R.
ferrugineus. Specific objectives were to (1) determine the seasonal
variations of abundance of adults RPW and the effectiveness of pheromonefood
baited traps for monitoring and controlling populations, (2) determine
the effect of trapping on the level of infestation by RPW to date palm trees,
and (3) determine the release rates of the tested pheromone lures.
MATERIALS AND METHODS
Pheromone Lures
Five aggregation pheromone lures were evaluated for RPW catch in
the field (Figure 1). Lures were different in their components and thickness
of their walls that affect the release rate, also differences in the % purity of
the active ingredient. One registered commercially available pheromone lure
was used under the trade name ferrolure+ or pheromone lures
Rhynchophorus ferrugineus (ChemTica International Co., Costa Rica). The
components of this pheromone lure are 4-methyl 1-5-nonanol (9 parts) + 4-
methyl nonanone (1 part) - purity 99.9% + 0.1% colorant and 0.1%
antioxidant. Ferrolure+ was compared with four other pheromone lures
contained 4-methyl-5-nonanol (96.5% purity) with isomers (4S, 5S- = 30%,
4R, 5R- = 30%, 4R, 5S- = 20%, 4S, 5R- = 20%) (SciTech, Czech Republic
and IPM Technologies, USA). In our study, ferrolure+ called pheromone 7
or pheromone control; the other four pheromone lures called pheromone 5, 6,
8, and 9. Pheromones 7 and 8 contained an attractant.
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Figure 1. Various types of pheromone lures used for monitoring R.
ferrugineus.
Components of the Pheromone-Food Baited Trap
The standard pheromone-food baited trap (figures 2 and 3) used in
UAE farms consisted of (a) a 10 liter plastic bucket covered from the outside
by a rough cloth to allow the adult weevils to crawl up easily on the trap to
reach the inside through the openings, rather than falling down from the
smooth surface of the bucket; the bucket had a four 2.5 x 6 openings for the
entrance of the attracted adults, (b) Soft date fruits placed at the lower part of
the bucket as baits, (c) a granular insecticide diazinon placed on the top of
the date fruit to kill adults upon arrival, (d) a pheromone lure to be hanged
from underneath of the bucket cover, and (e) a water to wet the insecticide,
treated date fruits.
Figure 2. Components of the pheromone-food baited traps: (a) a plastic
bucket covered with a rough cloth, (b) date fruit, (c) an insecticide, (d)
pheromone lure, and (5) water.
e d c b akeh
32 9
Figure 3. Preparation of the pheromone-food baited traps. (a) adding an
insecticide to the date fruit at the lower part of the plastic buckets, and (b)
hanging the pheromone lure to the underneath of the bucket lid.
Trap maintenance was required during the experimental period. Traps
were inspected weekly, during the experimental period, to replace the
insecticide-treated dry date fruits and add water as needed.
Pheromone-food baited traps were placed on the ground with the lower
half of the trap inserted in the ground between the date palm trees. Traps
located at ground level captured significantly more weevils than those
located at 1.7 m, and the latter captured significantly more weevils than traps
located on poles at 3.1 m (Oehlschlager et al. 1993).
Figure 4. Placement of the pheromone-food baited trap between the date
palm trees.
Field Study Sites
a
b
33 0
Experiments to evaluate five aggregation pheromone lures were
carried out between March 1998 and May 1999. Ten commercial farms, in
Al-Ain (UAE), were selected for the tests in which two farms were used to
evaluate each of the five pheromone lures. Farms contained trees 7-15 year
old. The distance between trees ranged from 4 to 6 m. Table 1 shows the
total number of pheromone-food baited traps and the number of date palm
trees for each pheromone treatment.
Table 1. Total number of traps for each pheromone lure, and the total
number of date palm trees in the two farms used for each pheromone lure.
Pheromone
Lure No.
Total No.
of Farms
Total No.
of Traps
Total No. of
Trees
5 2 6 1148
6 2 6 1014
7 (control) 2 7 1187
8 2 8 1558
9 2 6 900
Effect of Trapping on Population Patterns and Level of Infestation
The effect of trapping on population spatial patterns was based on (1) the
number of weevils caught per trap per specific period, and (2) the level of
infestation that occurred during the experimental period. Traps were
inspected weekly during the experimental period and the number of adults
RPW were counted and collected. Trapped adults were identified as males or
females and the ratio of female/male was determined. Date palm trees were
inspected during the experimental period to determine if new infestations
occurred. Pheromone lures in all traps were replaced monthly with new
ones.
Pheromone release Rates
Because the release rate of a lure is considered one of the factors
influencing the efficacy of the pheromone in attracting the adults, the lures of
all pheromones evaluated in the tests were monitored for their release rates.
Lures were placed in the traps (similar to the traps placed in the field) (n = 6).
The weights of all lures were recorded before placing them in the traps, and
every few days thereafter. The net weight of the pheromones in each lure
type varied (pheromone 5 = 297 mg, pheromone 6 = 331 mg, pheromone 7 =
752 mg, pheromone 8 = 605 mg, and pheromone 9 = 328 mg). The percent
loss of the pheromone in the dispenser was calculated.
33 1
Figure 5. Weekly inspection of the pheromone-food baited traps for
counting the number of adults RPW.
RESULTS AND DISCUSSION
Seasonal Variations of Abundance of RPW
Figure 6 shows a fluctuation of RPW population, during the growing
season, as indicated by trap catches of five pheromone lures used. This
fluctuation can also be noted between each week of each month. There were
two population peaks during 1998 tests (March to December 1998): the first
major peak started from early-March and ended mid-May (with a small peak
from mid-May to mid-July). The highest trap catch during this period was 8
adults per trap for pheromone 7 on 31 March, 6.3 adults per trap for
pheromone 5 on 14 April, and 3.6 adults per trap for pheromone 6 on 24
March. The second major peak (which was smaller than the first major peak)
started from mid-September and ended late-December, 1998. The highest
trap catch during this period was on 10 October, where 5 adults were caught
per trap for pheromone 7, 3.5 adults per trap for pheromone 5, 3 adults per
trap for pheromone 6, and 2 adults per trap for pheromones 8 and 9. Results
for the high capture rates during the first peak agree with those reported by
El-Garhy (1996) and El-Ezaby (1998). El-Garhy (1996) reported that the
high catch rates during the period from April to June probably due to the
emergence of broods whose development was slowed by the cooler winter
months.
33 2
33 3
Fluctuations in the average minimum and maximum temperature and
percent humidity during the tests were recorded. Trap catch during March, April,
and early-May was higher than those recorded during June and July; the temperature
at the first period was lower. The very low numbers of weevils were caught during
July, August, and September where very high temperatures were recorded. Trap
catch increased from mid-September where average maximum temperature was less
than 40C.
Effect of Trapping on the Level of Infestation
The level of infestation prior to the initiation of the tests and during the
pheromone trials is reported in Figures 7 and 8. The total number of infested
date palm trees in the ten farms used for our pheromone trials was
significantly decreased compared with the previous years where chemicals
were used for RPW control. Figure 7 shows a comparison of the
pheromones 5, 6, and 7 (evaluation from March 1998 to March 1999). The
number of infested trees reported for 1987 season (i.e., one year before
stating the pheromone trials) was 21, 13, and 7 trees for treatments of
pheromone 5, 6, and 7, respectively. The number of infested trees during
pheromone trial period was 2, 10, and 0 trees for treatments of pheromone 5,
6, and 7, respectively. This corresponds to a percentage reduction of
infestation equal to 90.4, 23.1, and 100%, respectively. The average number
of adult weevils per trap per month was 65.2, 48.5, and 112.0 adults for the
treatments of pheromone 5, 6, and 7, respectively.
Figure 8 shows a comparison of the pheromones 8, 9, and 7
(evaluation started June 1998). The number of infested trees reported for
1987 season (i.e., one year before stating the pheromone trials) was 11, 2,
and 5 trees for treatments of pheromone 8, 9, and 7, respectively. The
number of infested trees during pheromone trial period was 1, 2, and 0 trees
for treatments of pheromone 8, 9, and 7, respectively. This corresponds to a
percentage reduction of infestation equal to 90.9, 0, and 100%, respectively.
The average number of adult weevils per trap per month was 23.6, 18.7, and
65.2 adults for the treatments of pheromone 8, 9, and 7, respectively.
The overall performance of pheromone dispensers was very good
(especially if we correlate the trap catch with the level of new infestations
occurred in the farms during the pheromone trial period). The performance
of the RPW dispensers (in order), based on trap catch data after one year of
33 4
33 5
33 6
trapping, was pheromone 7, 8=5, 6, and then 9. In addition, pheromones 7, 5, and 8
protected palm trees from infestations during the pheromone trials period, with one or
two infestations reported for treatments of pheromones 5 and 8.
Sex differences in trap catch were noticed. Both sexes were attracted
to traps, but the number of females captured in the traps was higher than
male weevils (Table 2). Female: Male ratios were 1.5 for the pheromone
lures 5, 6, and 7 evaluated during the first population peak. The sex ratio
during the second population peak was 2.8 for pheromone 5 and pheromone
6.0, 1.9 for pheromone 7, and 2.2 for both pheromones 8 and 9. El-Garhy
(1996) reported that twice as many female as male weevils were captured.
The higher number of females than males in the traps may be due to that
females may disperse more than males in order to find a suitable food source
for their progeny. Also, the aggregation pheromone released from males
may have attracted females more than males. The ability of the tested
pheromones to capture more females than males in the traps makes trapping a
potential tool for managing this economic insect.
Table 2. Total trap catches of females and males during the two population peaks
(first peak period: from March 3 to May 19; second peak period: from
September 19 to December 19).
First Peak Second Peak
Pheromone ---------------------------------- ----------------------------------
Lure No. Female Males Ratio (F/M) Females Males Ratio (F/M)
5106 70 1.51 75 27 2.8
6 108 71 1.52 61 22 2.8
7 163 109 1.50 122 64 1.9
8 - - - 62 28 2.2
9 - - - 31 14 2.2
F/M = females/males ratio
Pheromone Release Rates
The release rates of the five pheromone lures (regardless of initial
weight of each pheromone in the lures) during the 32 days of hot weather,
from May 23 to June 24 of 1998, are shown in Figure 9. The average
minimum temperature during this period was 27.3ºC, average maximum
33 7
temperature was 43.5ºC, the average minimum humidity was 15.8% and the
average maximum humidity was 52.1%. A complete release (100%) of the
pheromone from the lures was noted after 7 days for pheromone 5 (42.5
mg/day; too fast) and 7 days for pheromone 6 (47.0 mg/day), 22 days for
pheromone 7 (34.0 mg/day) and 22 days for pheromone 8 (27.5 mg/day), and
32 days for pheromone 9 (10.2 mg/day). The time period needed for a
complete release of pheromone 8 was similar to that of pheromone 7, the
amount of pheromone released per day was higher for pheromone 7 (34.0
mg/day) compared with those of pheromone 8 (27.5 mg/day). The best lures
used, based on the release rate was pheromone 9 with 10.2 mg released per
day.
Figure 10 shows the release rates of the five pheromone lures during
73 days of cool weather, from November 25 of 1998 to February 6 of 1999.
Release rates slowed during the cooler days. During this period, the average
minimum temperature was 17.3ºC, average maximum temperature was
30.0ºC, the average minimum humidity was 18.5% and the average
maximum humidity was 88.0%. Pheromones from all lures were not released
completely after 73 days. Only 9% of the pheromones was released from
pheromone 9 (0.44 mg/day; too slow during this cool weather), 40% from
pheromone 7 (4.0 mg/day), 60% from pheromone 6 (2.8 mg/day), 75% from
pheromone 5 (4.4 mg/day), and 85% from pheromone 8 (7.0 mg/day).
The use of pheromones in monitoring and controlling RPW
populations has become an important tool for managing this pest (Kaakeh et
al., 2001). The factors that influence the ability of pheromone-food baited
traps to monitor populations of RPW include the following: dose, ratio, and
release rate of the pheromone blend from the lure (Jansson et al., 1990;
Sanders, 1992; Pfeiffer et al., 1993a, b), effectiveness of the blend at a
variety of population densities (Sanders 1992), lure type (Sanders and
Meighen 1987), species specificity of the pheromone blend (McLaughlin and
Heath, 1989), longevity of the lure over the trapping period (Jansson et al.
1990), trap position or location (Howell et al., 1990; Oehlschlager et al.,
1993), trap color (Oehlschlager et al., 1993), trap density (Houseweart et al.
1981, Oehlschlager et al., 1993), repellency of killing agents or dead insects
within the trap (Sanders 1986), the effect of weather on trap catch (Pitcarin et
al., 1990) and ease of management and cost of monitoring (Sanders 1992).
33 8
33 9
34 0
There are several benefits for using the pheromone-food trapping system (Kaakeh
2000): (1) monitoring traps indicate where RPW populations are highest, (2) mass
trapping can intercept invading weevils from abandoned farms and, in turn, can lower
the risk of new infestation from these weevil hot spots, and (3) efficient trapping can be
a substitute for insecticide control during fruit maturation and harvesting. Farmers in
UAE should be aware of the seriousness of the RPW problem. This can be achieved by
encouraging and training farmers to conduct trapping system for RPW monitoring
and/or control, and obtain some experience with trapping. There is a need to initiate
mass trapping in heavily infested and abandoned farms. Trapping might remove
sufficient proportions of emerging weevils that mechanical destruction of these farms
might not be necessary. In addition, national integrated management program for the
RPW should be implemented using a pheromone trapping system in all agricultural and
urban areas. The government should have the coordinating and regulatory authority.
The results presented here are promising in utilizing pheromones for
significantly reducing RPW populations and for protecting date palm trees
from RPW infestations within the field. Further studies should be conducted
to understand the RPW-date palm tree interaction and the factors affecting
their behavior in the laboratory and the field (Kaakeh, 1998). These include
the study of the effect of environmental and physiological factors on mating
frequency of RPW, weevil activities in the presence or absence of host odor
or frequency of RPW activities in the presence or absence of host odor or
food, and time of day in which mating occurs. Knowledge on the function of
aggregation pheromones in the mating behavior of RPW is also important for
the development of pheromone application in controlling the destructive pest.
ACKNOWLEDGEMENTS
The contribution of pheromone lures by IPM Technologies, USA is
appreciated. This study was supported by the United Arab Emirates
University and the Department of Agriculture and Livestock, Al-Ain, UAE.
34 1
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