RPW Mass Rearing

MASS REARING OF THE RED PALM WEEVIL,
RHYNCHOPHORUS FERRUGINEUS OLIV., ON SUGARCANE AND
ARTIFICIAL DIETS FOR LABORATORY STUDIES:
ILLUSTRATION OF METHODOLOGY
Walid Kaakeh, Mahmoud M. Abou-Nour, and Ahmed A. Khamis
Department of Plant Production, Faculty of Agricultural Sciences,
UAE University, P. O. Box 17555, Al-Ain, U.A.E.
ABSTRACT
A method for laboratory mass rearing of the red palm weevil
(Rhynchophorus ferrugineus Oliv.) (RPW) were developed. Weevils,
initially obtained from the field, were maintained on the stems of sugarcane.
Prior to mass rearing, several artificial diets were formulated and preliminary
evaluated for development of the R. ferrugineus. Materials used for
preparations of various diets were: oats, coconut cake, coconut fruit pieces,
canned and/fresh pineapple, sucrose, molasses, egg yolk, salt, yeast,
vegetable oil, potatoes, soybean flours, date palms leaves and palm fiber
sheath, sugarcane fibers, bacto-agar, multi-vitamins, preservatives, and
water. Oat and white bean diets were preferred by 1st to 3rd larval instars,
while oats + fibers preferred by 4th to 5th larval instars. Larvae fully
developed on artificial diets and molted four times during their development
failed to construct cocoons because of the unavailability of fibers (palm or
sugarcane. Facilities, materials required, diet preparation and procedures,
and practical difficulties of rearing methods are discussed.
Additional Index Words: Rhynchophorus ferrugineus, pheromone,
trapping, palm trees
INTRODUCTION
The red palm weevil (RPW), Rhynchophorous ferrugineus Oliver
(Coleoptera: Curculionidae), is an economically important, tissue-boring
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 (Lal, 1917; Buxton, 1918). 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).
34 5
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).
Red palm weevil is a concealed tissue borer and spends all of its life
stages inside the palm tree. Damage symptoms can be categorized by one or
more of the following (Abraham 1998): presence of the tunnels on the trunk
and base of leaf petiole made by the feeding grubs, oozing out of thick
yellow to brown fluid from the tree, appearance of chewed up plant tissue in
and around openings in the trunk, presence of a fermented odor from the
fluid inside infested tunnels in the trunk, presence of adults and cocoons in
the leaf axils, fallen empty pupal/chewed up frass on the ground around the
palm, breaking of the trunk or toppling of the crown when the palm is
severely infested.
Research on the biology and control of R. ferrugineus, for many
projects conducted in the last four years at UAE University by various
researchers, required large numbers of weevils of various stages. First
attempt to develop a method for mass rearing of this pest was made by the
authors during this period in the UAE. Rearing methods of this and several
related species were reported in other countries and with similar species
(Rahalkar et al., 1972, 1978, 1985; Rananavare et al., 1975; Giblin-Davis et
al., 1989; Weissling and Giblin-Davis, 1995). The objectives of this study
were to (1) illustrate the methodology of mass rearing R. ferrugineus on
sugarcane, and (2) develop artificial diets for rearing R. ferrugineus.
MATERIALS AND METHODS
Insects
Various stages of R. ferrugineus were collected from infested date palm
trees in Masafi area in Sharja Emirate in 1997. Each developmental stage
was placed individually in covered plastic container. Portable wood saw
was used to facilitate collecting weevils from heavily infested palm trees
(Figure 1).
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Figure 1. Collection of various stages of R. ferrugineus from infested date
palm trees.
Rearing Room
Rearing of R. ferrugineus of various stages was carried out in a
controlled rearing room at the Plant Protection Laboratory of the Plant
Production Department, UAE University (Figure 2). The room was
maintained at 25 ± 2ºC and 60-70% RH. The photoperiod was approximately
12:12 L:D. The room contained three large working benches, electrical
outlets, stainless steel sink, side boards, autoclave, and a refrigerator. The
room was also used as a media room for handling and preparing materials of
artificial diets.
34 7
Figure 2. Room for rearing R. ferrugineus at the Faculty of Agricultural
Sciences, United Arab Emirates University.
Equipments and Materials
Equipments and materials required for rearing R. ferrugineus on
sugarcane and artificial diets are given in Table 1.
Rearing on Sugarcane
Adults. Adults collected from the field (Figure 1) were cleaned and
kept (as group of at least 10 males and females but not sexed) in rectangular
plastic boxes with press-on tight-fitting lids, or kept as individual pairs of
males and females in 1 liter glass jars (Figure 3). All adults were provided
with at least 5 absorbent cotton wicks saturated with a 10% honey solution
for feeding and egg laying. Boxes and jars were staked side by side (or on
the top of each other) on working benches. Few holes were made on all lids
of boxes and jars for ventilation. Females lay their eggs on the cotton wicks
(i.e., oviposition site). Association of both sexes for 24 h ensures fertilization
of females and no further mating of females was necessary (Kaakeh, 1998).
Adults after emergence from cocoons were sexed and kept separately in
small jars for mating and egg laying. Sexing the adults was done according
to the presence of a series of black hairs on the dorsa, frontal part of snouts
of males and their absence in the females.
34 8
Table 1. Equipments and chemical materials used for rearing R. ferrugineus
on sugarcane and artificial diets.
• Blanace (up to 3 kg; triple beam balance or others)
• Electric blender/mixer
• Autoclave
• Refrigerator
• Portable wood cutting saw
• Rectangular plastic boxes
• Polyethylene collecting buckets
• Aluminum and plastic trays or boxes (various sizes) with tight-fitting
lids
• Glass and disposable plastic Petri dishes (50 and 100 mm In diameter)
• Camel-hair brushes (no. 2 preferred)
• Absorbent cotton or cotton wicks (sheets and bolls)
• Scissors
• Glass jars (1 liter)
• Measuring cylinders (50, 100, 200, and 500 ml)
• 40-mesh nylon netting
• Cork borer set
• Aluminum foil
• Transparent, polyethylene bottles, with tightly closing lid.
• Black fiber paper sheets
• Rubber bands
• Paper towels
• Absorbent cotton wicks
• Hand magnifiers
• Labpette digital micro-pipet, capacity 1-20 micro-liter
• Parafilm rolls (for sealing test tubes, flasks, Petri dishes, etc.)
• Eye wash bottles
• Disposable non-toxic particle masks
• Graduate and funnel brushes
• Glass shell and screw-cap vials
34 9
Figure 3. Rectangular plastic boxes and glass jars holding adults for mating
and oviposition. Plastic containers contained unsexed groups of
adults, while the glass jars hold pairs of sexed males and females.
Eggs. Cotton wicks holding eggs were removed from the oviposition sites
(i.e., large plastic boxes and small glass jars in figure 3) and placed in
separate boxes (Figure 4). Cotton wicks were wet with water to avoid
drying. Other eggs were transferred with the camel hair brush and placed on
wet filter papers inside the petri dishes for further studies. New cotton wicks,
saturated with a honey solution, were placed in all containers holding the
adult stages. After 2 to 3 days, larvae from hatched eggs were removed to
separate containers and provided with pieces of sugarcane stems for feeding.
Larvae. Newly hatched larvae on cotton wicks were transferred with a
camel’s hair brush to pieces of sugarcane stems (at least 15 mm in diameter)
(Figure 5). A small hole was made at the end of each piece of sugarcane
stem using a cork borer. One week after feeding, larger larvae were
transferred to larger fresh pieces of sugarcane stems (10 – 40 mm in
diameter; this was based on the size of larvae at different developmental
stages). Last larval instars made cocoons from the fibers inside the sugarcane
stems. When sugarcane was infested with Drosophilla flies, yellow sticky
traps were placed above the rearing containers as a control tool. Also, larvae
were reared individually (Figure 5) in sugarcane stems to avoid cannibalism.
35 0
Figure 4. Egg collection from cotton wicks and filter papers.
Figure 5. Handling and feeding of larvae in sugarcane stems.
35 1
Pupae. After 10-14 days of feeding of last larval instars, the stem pieces of
sugarcane were split open and cocoons were collected. Cocoons were placed
in a plastic containers or metal trays, wet with water as needed, and closed
with lids. Two weeks after collecting the cocoons, they were checked daily
for adult emergence. Adults were collected by hand and placed in plastic
containers (as unsexed groups of adults) or placed individually in glass jars
(as sexed, paired males and females).
Figure 6. Collection of pupae of R. ferrugineus from pieces of sugarcane
stems (a) and plastic containers holding cocoons (b).
Rearing on Artificial Diets
Preparation of Diets
Artificial diets were prepared for mass rearing of R. ferrugineus
because of the unavailability of sugarcane in UAE and this was a limiting
factor in culturing this insect. Diets were also developed to avoid the use of
expensive palm tissues for culture of weevils.
Table 2 lists materials used for the preparation of several artificial
diets. Different diets were evaluated in preliminary tests for larval and adult
biomass gain, survival, and the rate of development Three diets were
selected (Figure 7) and percentage of dry ingredients is listed in Table 3.
Diet A is an mainly an oat diet, Diet B is an oat diet plus palm and coconut
tissue, while diet C is mainly a white bean diet. Ingredients and water (1 - 2
liter of water for diets weighing 500 - 1000 g) were blended for
approximately 5 minutes. All diets included bacto-agar, multi-vitamins,
chemical preservatives. Bacto-agar was dissolved in water and added to
other ingredients. The mixtures of all diets were then autoclaved for 20 min
at 120ºC. Diets were poured in diet stainless-steel round trays or cups while
still warm. All trays and cups were stored at room temperature until
a b
35 2
required. Larvae were placed on diets after total coolness. As with rearing
R. ferrugineus on sugarcane, when artificial diets were infested with
drsophilla flies, yellow sticky traps were placed above the rearing containers
as a control tool. Also, fungal and bacterial contamination may develop if
chemical preservatives were not incorporated in the diets. This may also
occur if high quantity of water was mixed with the dry ingredients of diets.
Table 2. Materials used for the preparation of artificial diet for rearing R.
ferrugineus in the laboratory.
Food Materials
Oats Date palm leaves and fiber sheath
White beans Canned or fresh pineapple
Sugarcane bagasse Soybean flours
Fresh sugarcane stems Coconut fruit pieces
Fresh coconut cake Coconut fibers
Potatoes Vegetable oil
Egg yolk Wesson salt
Vitamin tablets* Brewer's yeast or other brands
Honey
Chemical preservatives
Methyl para-hydroxybenzoate **
Auromycin
4M Potassium hydroxide***
Sorbic acid****
Bacto-agar
___________________________________________________________
* vitamin tablets contained vitamins A, B1, B2, B6, B12, D2, E, K1,
Riboflavin, nictotinamide, and others.
** 14% solution In 95% ethyl alcohol. 5 ml water was added to 95 ml
absolute ethyl alcohol (95% solution) and then 140 g methyl parahydroxybenzoate
was dissolved in 95% ethyl alcohol (amount of 15
ml solution per 1 kg diet was used)
*** 56 g potassium hydroxide in 250 ml distilled water (the amount of use
5 ml solution per 1 /kg of diet was used).
**** 12.5% stock solution In 95% ethyl alcohol. About 125 g sorbic acid
was dissolved in 1 liter of 95% ethyl alcohol (the amount of 15 ml
solution per 1 kg of diet was used) (Rahalkar et al. 1985).
35 3
Table 3. Percentage of dry ingredients of three artificial diets used for
rearing R. ferrugineus.
% Dry Ingredient in
________________________________________
Dry Ingredient Diet A Diet B Diet C
Oats 57 48 15
White Beans - - 65
Palm and coconut tissues - 15 -
Sugar 22 19 10
Molasses 11 10 -
Brewers yeast 9 7 9
Salt 1 1 1
Figure 7. Artificial diets in small plastic trays or cups or in stainless steel
containers for feeding of larvae of various sizes.
Larval Feeding on Artificial Diets
Prior to mass rearing, several artificial diets were formulated and
preliminary evaluated for development of R. ferrugineus. Second instar
larvae were washed in tap water, weighed, and placed into holes made on
artificial diets to facilitate feeding. Larvae were transferred one per diet cup
with a fine camel hair brush (Figure 8). The weight for each larva (n = 8)
was recorded weekly for 6 weeks, and was then compared with its starting
35 4
weight. When larvae reached the end of the last larval instar, they were
placed in the stems of sugarcane for constructing cocoons. Diets were
checked daily for any dead larvae in which they were replaced.
Figure 8. Feeding of larvae on artificial diets.
RESULTS AND DISCUSSION
Previous attempts that were made by several researchers followed
several steps: Sugarcane was a good substitute for coconut for rearing R.
ferrugineus (Rahalkar et al., 1972); sugarcane was later incorporated in
nutrient agar for feeding young larvae and sugarcane stem pieces for feeding
of older larvae (Rananavare et al. 1975). Rahalkar et al. (1978, 1985)
improved the culture of R. ferrugineus by developing an artificial diet
containing sugarcane bagasse (fiber), coconut cake, yeast, sucrose, minerals,
vitamins, and preservatives. Giblin-Davis et al. (1989) cultured R. cruntatus
and R. palmarum on decomposing pineapple. In our study, there were
variations in the quality of developed diets made using different ingredients.
Diet A was mainly made by oats, diet B was made using oats and fibers,
while diet C was made using white beans. Diets A and B were preferred by
young larvae (1st to 3rd larval instars) while diet B was preferred by older
larvae (4th and 5th larval instars).
35 5
The average biomass of larvae at various stages, survival, percentage
of larvae that went into cocoon, and biomass and percentage of emergence of
adults varied greatly between the diets tested: a range of larval biomass after
three weeks of feeding on artificial diets was 0.25 – 2.5 g and after 5 weeks
was 0.5–4.5 g. The weight gained from feeding increased considerably in a
three week period (i.e., larvae with weight ranged from 0.5 to 0.11g
increased 40 to 80X, that is 4.18 to 4.54 g). The weight gained varied with
the type of diet provided to the larvae. The percentage of larval survival
ranged from 10 to 90%. The biomass of emerged adults ranged from 0.8 to 2
g. The percentage of adult emergence ranged from 10 to 80%.
Larvae were fully developed on artificial diets and molted four times
during their development (Figure 9). These larvae failed to construct
cocoons because of the unavailability of fibers (palm or sugarcane) or there
was not enough quantities of high fiber substrates in diet B. All larvae fed by
either of the three artificial diets were transferred to sugarcane stems for
making cocoons. Additional studies are required to search for alternative
food sources to develop diets that R. ferrugineus can fully develop on it
without transferring last larval instar to sugarcane stems for cocoon
construction.
Figure 9. Development of first instar larvae on artificial diet (a), and the
molting of fourth instar larva to the fifth larval stage.
The success of our three artificial diets (Table 3) in providing the necessary
nutritional requirement for molting and development was based on data
recorded ing various life parameters of R. ferrugineus on sugarcane and
artificial diets (a study conducted by the authors, see the next manuscript in
this proceedings). The study on life parameters of R. ferrugineus included
the following: fecundity or the number of eggs per female, egg viability or
the percentage of hatch, larval developmental period, larval biomass, pupal
35 6
period, percentage of larval survival, percentage of adult emergence,
fecundity, fertility, and female:male ratio.
LITERATURE CITED
Abraham, V. A., M. A. Al-Shuaib, J. R. Falleiro, R. A. Abozuhairah, and P.
S. P. V. Vidyasagar. 1998. An integrated management approach for
the red palm weevil Rhynchophorus ferrugineus Oliv. A key pest of
date palm in the Middle East. 3: 77-83.
Buxton, P. A. 1918. Report on the failure of date crops in Mesopotamia in
1918. Agric. Directorate, M. E. F. Bassarah Bull. No. 6.
Cox, M. L. 1993. Red palm weevil, Rhynchophorus ferrugineus, in Egypt.
FAO-Plant-Protection-Bulletin 41: 1, 30-31.
Giblin-Davis, R. M., T. J. Weissling, A. C. Oehlschlager, and L. M.
Gonzalez. 1994. Field response of Rhynchophorus cruntatus
(Coleoptera: Curculionidae) to its aggregation pheromone and
fermenting plant volatiles. Florida Entomol. 77: 164-177.
Lal, Madan Mohan. 1917. Rept. Asst. Prof. Entomol; Rept. Dept. Sagr.
Punjab, for the year ended 30th June, 1917.
Lefroy, H. M. 1906. The more important insects injurious to Indian
Agriculture. Govt. Press, Calcutta, India.
Kaakeh, W. 1998. The mating behavior of the red palm weevil,
Rhynchophorus ferrugineus Oliv. (Coleoptera: Curculionidae). Emir.
J. Agric. Sci. 10: 24-46.
Rahalaker, G. W., M. R. Harwalkar, and H. D. Rananavare. 1972.
Development of red palm weevil, Rhynchophorus ferrugineus Oliv.
Indian J. Entomol. 34: 213-215.
Rahalaker, G. W., A. J. Tamhankar, and K. Shanthram. 1978. An artificial
diet for rearing red palm weevil, Rhynchophorus ferrugineus Oliv. J.
Plantation Crops 6: 61-64.
Rahalaker, G. W., M. R. Harwalkar, H. D. Rananavare, A. J. Tamhankar,
and K. Shanthram. 1985. Rhynchophorus ferrugineus, pp. 279-286. in
35 7
P. Singh and R. F. Moor [eds.]. Handbook of insect rearing. Elsevier,
New York, NY. Vol. 1.
Rananavare, A. J. K. Shanthram, M. R. Harwalkar, and G. W. Rahalkar.
1975. Method for the laboratory rearing of red palm weevil,
Rhynchophorus ferrugineus Oliv. J. Plantation Crops 3: 65-67.
Weissling, T. J. and R. Giblin-Davis. 1995. Oligidic diets for culture of
Rhynchophorus cruntatus (Coleoptera: Curculionidae). Frlorida
Entomologist 78: 225-234.

Red Palm Weevil Control Management

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.
32 6
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.
32 8
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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