Introduction

MacGregor and Gutiérrez (1983) mentioned the American palm weevil ( Rhynchophorus palmarum L.) attacking coconut palms ( Cocos nucifera L.), oil palms ( Elaeis guineensis Jacq), common date palms ( Phoenix dactylifera ), papaya trees ( Carica papaya ) and banana trees ( Musa paradisiaca ). This insect (Coleoptera, Curculionidae) is known in Mexico as "mayate prieto del cocotero", and "picudo de la palma" in Central America. In Mexico, its presence was originally reported in the states of Guerrero and Tabasco in papaya and coconut trees (Domínguez and Carrillo 1976). 

González and Camino (1974) found that females could lay up to 63 eggs per day for a total of 924 eggs throughout their lives. There are nine larval stages which may cause a lot of damage by boring into shoots and stems. Pupation occurs in the periphery of the stem (10-14 days), and adults go through a pre-copulative stage of four to six days. They have the potential to copulate throughout their entire lives, which can last up to two months. 

Camino et al . (1998) reported that this insect has a circadian rhythm of feeding and copula, that adults can survive under water for long periods of time, and that they have been found in papaya roots at one meter under the soil, coexisting with their larvae.

González and Camino (1974) determined that dwarf coconut was very susceptible to "red ring", a disease caused by the nematode Bursaphelenchus cocophilus , which is transmitted by R. palmarum . On a young coconut plantation in La Chontalpa, 85% of the plants died as a result of this disease. Noriega et al . (1991) found an annual incidence of red ring of 3% in the Costa Chica region and 5% in the Costa Grande region in the state of Guerrero. It was also found that trees near banana and papaya plantations were those most affected.

Camino (1975) described, in Tabasco, a trap called CSAT ( Fig. 1 ) for capturing palm weevils, using pineapple or banana as a food source. The trap consisted of a pail with a bowl inside, where bait (2 kg) was placed. The traps were hung 1.20 m above the ground. Later, Camino and Jiménez (1994) used the CeProBi trap, a modification of the CSAT trap, in Morelos. Santos et al . (1996), in Coyuca de Benítez and Atoyac, Guerrero, were very successful with the use of the pheromone Rhynko-Lure®, produced by ASD in Costa Rica, with banana as a food bait and Lannate 0.2%. The trap they used was similar to the CeProBi type, which they denominated the "Guerrero trap". Santos et al . (1996) found an incidence of red ring between 10% and 45% and determined that with intensive trapping they could significantly reduce the disease incidence in two to three months. 

The concept of integrated pest management (IPM) implies the reduction of the economic damage caused by a pest while at the same time reducing the risk of causing undesirable secondary effects on the environment. The use of traps using food baits and pheromones fits very well into this scheme.

There are many examples in the literature where different trap designs, food baits and pheromones have been used to manage pests within an IPM scheme. The following are some specific cases related to R. palmarum .

Hagley (1965), in Trinidad and Tobago, found that decomposing fruits attracted the insect. Maharaj (1973) described a trap to capture the insect using coconut trunks impregnated with Lannate insecticide. Camino (1975) described a trap made of a pail, a bowl and a glass bottle ( Fig. 1 ). 

The CSAT trap, a yellow one, placed 1.20 m above the ground, baited with banana or pineapple, was better than the Maharaj trap.

Rochat et al. (1991) obtained the aggregation pheromone from the R. palmarum male, which they identified as 2-metil-5(E)-hepten-4 ol (rhynchophorol). This pheromone was the basis for developing an integrated pest management program for the palm weevil and red ring disease in oil palm in Central America (Chinchilla and Oehlschlager 1992, Chinchilla et al . 1993, Oehlschlager et al . 1993).

Camino et al . (1992) tested several compounds derived from ripe pineapples (Ping Wu et al . 1991) and found that ethyl acetate was the most attractive to the insect in laboratory conditions.

According to Chinchilla (1998), the efficiency of a trap program to capture the American palm weevil and to control the red ring disease depends on trap location, density and maintenance, training of the personnel involved and the promulgation of laws to force farmers to maintain an acceptable level of phytosanitary management.

This note describes the effectiveness of a method to capture R. palmarum using the pheromone rhynchophorol (Rhyncho-Lure®, ASD de Costa Rica), within the concept of an integrated pest management in Costa Grande, State of Guerrero in México.

Materials and methods

The area studied includes Costa Grande, from Acapulco to Zihuatanejo, the coastal part of the State of Guerrero, which has a warm semi-humid climate with average annual temperatures of 22° to 26°C and total annual precipitation between 1000 and 2000 mm. 

This region is the main producer of copra in Costa Grande, and coconuts are mainly associated with banana and papaya plantations. At the present time, SAGAR is actively involved in the introduction of the oil palm as a new crop for the Mexican tropics, including Guerrero.

In all the tests, the commercial formulation of rhynchophorol (Rhynko-Lure®), sold by ASD de Costa Rica, was used. In addition, live male insects were used as a control together with several attractive volatile compounds.

Two experiments were done (from October 18th, 1997 to January 28th, 1998) using the following combinations of treatments: 

Petatlán (San Jeronimito) and Coyuca de Benitez (La Charamusca)

1. 2 kg of banana + 1 Rhynko-Lure® pheromone
2. 2 kg of banana + 4-5 live weevils 
3. 15 ml of ethyl acetate + ethanol+ iso-amyl acetate (proportion 1:1:1) + 4-5 live weevils
4. 15 ml of ethyl acetate + ethanol+ iso-amyl acetate (proportion 1:1:1) + 1 Rhynko-Lure® pheromone

Atoyac (Corral Falso) y Tecpan (Rodecia)

1. 2 kg of banana + 1 pheromone Rhynko-Lure®
2. 2 kg of banana + 4-5 live weevils

The baits of banana and volatile chemical substances were changed every two weeks, live insects were changed only when they died, and the pheromone Rhynko-Lure® was not changed during the experiment. Data was collected every two weeks.

Traps were hung on coconut trunks or in any fruit tree (generally mango) 1.20 m above ground level. One trap was hung every five coconut palms and a randomized complete block design was used with five replications. 

Collected insects were counted and separated by sex, and then a capture index was calculated using the following formula: 

IC = number of individuals collected / number of traps

Two more experiments were done between February 13th and December 11th, 1998:

Tecpan de Galeana (Rodecia) and Coyuca de Benítez (la Charamusca)

1. 2 kg of banana + 1 pheromone Rhynko-Lure® + 0.2 g of Lannate (WP)
2. 2 kg of banana + 1 pheromone Rhynko-Lure® + 1 funnel*
3. Volatile chemical substances (70 % ethyl acetate + 30% iso-amyl).

Corral Falso (Atoyac)

2 kg of banana + 1 pheromone Rhynko-Lure® + 1 funnel

The experimental plots had an approximate area of one hectare and the experiment consisted of 30 traps, with one trap placed every three or four palms.

The baits of banana and volatile chemical substances were changed every two weeks. The pheromone Rhynko-Lure® was changed when exhausted in the plastic capsule. The insects collected were counted and separated by sex, and then the capture index was calculated.

Results and discussion

During the first series of experiments, the highest capture indexes were obtained using the traps that had pheromone and banana as food baits ( Fig.2 , Fig.3 and Fig.4 ). Significant differences were found between capture values of the type 1 trap and the others (Kruskal-Wallis, P=0.05). The decrease in captures in Petatlán was associated with the disappearance of new cases of red ring disease. Capture indexes were higher in Tecpan as compared to other localities (Kruskal-Wallis, p< 0.05).

During the second round of experiments (February 13th to December 11th, 1988), the capture indexes of weevils were the highest for 20 consecutive samplings in Atoyac when treatment 2 (banana + Rhynko-Lure® + funnel) was applied. There were two periods when capture indexes were higher, from February to April and from September to November ( Fig.5 , Fig.6 and Fig.7 ).

In both places (Tecpan and Coyuca), for the 20 samplings made, significant differences were found between treatments. Treatment one turned out to be more effective than the other two (Kruskal-Wallis, p<0.001).

No statistically significant differences were found between capture indexes registered in Tecpan and those of Coyuca with treatment one (Kruskal-Wallis, p<0.001) and, as in Atoyac, there were seasonal variations in the capture indexes.

The capture index in Atoyac, using banana with Rhynko-Lure® for eight months, ranged from 0.6 to 0.8 and similar indexes were also obtained in Tecpan and Coyuca, where an insecticide was added to the traps. In other tests an additional benefit was apparent when insecticide was used, but it would be advisable to replace Lannate with another less toxic insecticide.

Traps with funnels did not capture more insects and, in addition, few captures were obtained when pheromone with volatile chemical substances was used; the food bait seems to be essential in achieving higher capture rates.

During the second round of experiments, it was found that captures of insects were lower in those localities with lower rainfall and less dense vegetation (Coyuca de Benítez and Petatlán). In Rodecia (Tecpan) and Atoyac (Corral Falso), areas with higher humidity and more dense vegetation, higher capture indexes were found.

This behavior could indicate that humidity is a critical aspect in the population dynamics of weevils in Costa Grande de Guerrero. In addition, crops associated with coconuts, such as bananas and mangos, would benefit the insect population, as would negligence in cleaning aspects (dead palms, fallen leaves, etc.). Another situation that favors the high density of the insect is the presence of swampy areas, which is logically related to high humidity.

In Coyuca, good attraction to treatment four was observed (volatile compounds with pheromone), but this phenomenon cannot be explained with the information available. Low humidity in the region could be affecting the behavior of the insect.

Recomendations

The population of R. palmarum could increase in Costa Grande, Guerrero with the expansion of dwarf coconut and oil palm plantations, and a program of phytosanitary protection should be begun in the region as soon as possible.

The trap containing 2 kg of bananas as a food source, the pheromone Rhynko-Lure® and insecticide can be recommended for our conditions. However, it is advisable to use an insecticide less toxic than Lannate, or to collect and manually eliminate the captured insects. Other food sources could also be tested.

Some high-priority areas should be selected for the control of weevils, primarily Tecpan and Atoyaca and then Coyuca de Benítez and Petatlán. In the primary areas, two or three traps per hectare could be used, with one trap per hectare in the other areas. The vegetation and associated crops must be considered important areas taken into consideration when placing traps (for example banana or mango as a neighboring or associated crop). 

Sampling should be intensified during and at the end of the rainy season. The weevil population in each area should be monitored, as well as the number of diseased palms before and during trapping.

It is important to train local personnel in the use of traps and the pheromone. Farmers could do the trapping, coordinated by SAGAR. It is necessary to take into consideration that the dwarf or hybrid coconut palm is replacing the typical tall palm, and thus, higher populations of weevils could be expected. 

The intensity of the captures should be increased before population peaks appear: January-February (spring) and June-July (summer). Finally, the control program will be more successful as more plantations remain free of sites where the weevils feed, breed and take refuge.

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