A PHEROMONE-BASED TRAPPING SYSTEM FOR MONITORING THE POPULATION OF COSMOPOLITES SORDIDUS

Gadi V.P. Reddy1*, Zerlene T. Cruz1, Fritz Naz1, Rangaswamy Muniappan2 Western Pacific Tropical Research Center, College of Natural and Applied Sciences 1 University of Guam, Mangilao, Guam 96923, USA IPM CRSP, OIRED, Virginia Tech, 1060 Litton-Reaves Hall, Blacksburg, VA 24061, USA 2 Received: October 22, 2008 Accepted: November 20, 2008 Abstract: The banana root borer Cosmopolites sordidus (Coleoptera: Curculionidae) is native to Malaysia and Indonesia but is found in nearly all banana-growing areas of the world. Studies were conducted to determine the pheromone trap efficacy, effect of shade on trap catches and to monitor the population of C. sordidus using pheromones in Guam. In Guam, pheromone traps were used to monitor the population level of C. sordidus. Before monitoring began, two basic studies were carried out, which established that pheromone-baited ramp traps positioned in the shade of the banana crop canopy caught significantly more adults than those placed in sunlight and that ramp traps baited with pheromone lures caught significantly more adults than did identical traps without pheromone lures. Ramp traps baited with pheromone lures were set up at each of 10 locations throughout the island in November 2005. Weekly counts were made of the borers caught by the pheromone traps.

The data indicated higher population levels (10 per week) in the northern region and low (5 per week) to medium level (5–10 week) populations in the southern part of the island. These differences among sites were highly significant. Linear and quadratic effects of rainfall on the number of borers captured were statistically significant, but according to quadratic regression models, the significance was due to differences at just one site.

Key words: Banana root borer, monitoring, Ramp trap, pheromones, Cosmolure+

INTRODUCTION

Although it attacks all types of bananas, including dessert and brewing, highland bananas and plantains, Musa paradisica L., also known as cooking bananas, are more susceptible (Gold et al. 2001; Sikora et al. 1989). The borers cause yield reductions by impeding sucker establishment in newly planted crops (McIntyre et al. 2001), loss of plant vigour and reduction in bunch size (Rukazambuga et al. 1998). The larvae of C. sordidus feed by boring or tunnelling through the plant, eventually causing corm decay by facilitating invasion by secondary organisms and leaving a mass of rotten tissue (Franzmann 1972; Gold et al. 2001). Such injury to the corm prevents nutrient uptake by the plant (Gold et al. 2001). If left uncontrolled, C. sordidus can reduce yield by up to 100% (Sengooba 1986; Koppenhoeffer et al. 1994).

The banana root borer is native to Malaysia and Indonesia but has spread to nearly all banana-growing areas of the world, including Australia, Africa, Central and South America, Florida, Mexico, the West Indies, some islands in the Pacific and South and Southeast Asia (Gold et al. 2001). It has been reported from the Marianas since the early 1940s (Gressitt 1954). In recent years, this borer has become a serious problem in commercial banana farms of Guam as well as other parts of Micronesia. All varieties of banana are attacked in Guam, although some preference has been noted for the Manila variety. Currently over 50% of the bananas marketed in these islands are imported, but quite a few commercial farms exist, and bananas are also grown commonly in many backyards and under subsistence farming conditions. Local farmers are steadily developing commercial farms. Currently, farmers in Guam and the Northern Mariana Islands use no definite control method against the banana borer.

Classical biological control of the banana borer, using natural enemies from Asia, has so far been unsuccessful (Gold et al. 2001). Only 15 generalist predators of the banana borer have been reported (Ostmark 1974). Several attempts at biological control throughout the Pacific have used predatory beetles, especially Plaesius javanus (Coleoptera: Histeridae) and Dactylosternus hydrophiloides (Coleoptera: Hydrophilidae), but they have been mostly ineffective (Weddell 1932; Ostmark 1974; Waterhouse and Norris 1987). Although the predators were established (usually after several attempts of introduction), their effectiveness was not well known and suspected to be minimal (Waterhouse and Norris 1987). Factors contributing to their poor effectiveness are their lack of specificity to the banana borer and the protected location of borer larvae and pupae in the tunnels within the banana plant (Ostmark 1974). These factors corroborate the findings of Gold et al. (2001) that biological-control programs for the banana borer have not been successful.

Synthetic pheromones can be used as tools for management of C. sordidus (Tinzaara et al. 2002). Evidence of a male-produced aggregation pheromone, to which both females and males of C. sordidus respond, was first provided by Budenberg et al. (1993). Beauhaire et al. (1995) detected six male-specific compounds in volatile collections that elicited electroantennogram (EAG) activity. They identified and synthesized sordidin, which was the most abundant of the volatiles. The absolute stereochemistry of the natural sordidin ((1S,3R,5R,7S)-(+)-1-ethyl-3,5,7-trimethyl-2,8diosabicyclo[3.2.1]octane) was subsequently determined (Mori et al. 1996; Fletcher et al. 1997). Ndiege et al. (1996) and Jayaraman et al. (1997) developed a large-scale synthesis of racemic sordidin that made field-testing possible. Its attractiveness to both males and females confirmed its function as an aggregation pheromone, and it was formulated at ChemTica International in Costa Rica as cosmolure + pheromone (Tinzaara et al. 2003). Use of cosmolure for trapping the borer in Costa Rica has been reported as a promising option (Alpizar et al. 1999; Oehlschlager et al. 2000).

Preliminary studies conducted in Uganda showed the pheromone to be up to 18-fold more attractive to C. sordidus than pseudostem traps (Tinzaara et al. 2000).

Farmers often complain about C. sordidus problems and the heavy damage sometimes caused to banana plantations, but there are limited studies for the control of this pest that have been conducted in the Pacific region. The objectives in the present study are to determine: (i) pheromone trap efficacy, (ii) effect of shading on pheromone trap catches, and (iii) population dynamics of C. sordidus in different areas of Guam using pheromone traps. Therefore, we have undertaken efforts to study the successful trapping method could increase our knowledge of the pest’s status so that appropriate methods could be adopted for its control. Such control could enhance economic development by reducing the cost of production and increasing the yield of bananas.

MATERIALS AND METHODS

Trap The ramp trap used is commercially available from ChemTica Internacional S.A.

(San Jos&, Costa Rica) (Fig. 1) (Reddy 2007). It was made of yellow durable polyvinyl chloride (PVC) and consisted of two square trays, each 14 cm on a side by 4 cm deep (inside dimensions). Four sloping ramps led from each of the four directions into the sides of the lower tray. Each ramp was 4 cm high, 13 cm long, and 12 cm wide and slid into a slot in the bottom tray. We ensured that each of the four ramps was in complete contact with the ground to allow borers to crawl into the traps. The upper tray, inverted and supported on four 6-cm posts, formed a roof over the bottom tray.

Water mixed with Joy concentrated dishwashing liquid detergent (Procter & Gamble, Cincinnati, OH) (1–3%) was poured into the bottom tray to retain adults that walked into the traps.

Pheromone lures Pheromone lures (Cosmolure+), sealed into polymer membrane release devices and optimized for C. sordidus, were obtained from ChemTica Internacional S.A. (San Jos&, Costa Rica). The lure packs, each containing 90 mg of pheromone and having a release rate of 3 mg/day (Tinzaara et al. 2005), were stored at 4°C until use. A lure was hung on a wire hook 2 cm below the centre of the roof of each trap. The lures were changed once or twice a month, although occasionally, more frequent changes were necessary. Old lures were discarded once liquid compounds were no longer visible.

Fig. 1. A ramp trap used to monitor Cosmopolites sordidus Pheromone trap efficacy Pheromone-baited and unbaited traps were placed at randomly chosen locations about 5 m apart on the ground in banana plantations in the villages of Dededo, Yigo, Hagåtña and Yoña (Guam, USA). The banana root borers trapped were removed and counted every week during this experiment. The traps were washed and rinsed, and new soapy water was added. We randomized the traps across the field to avoid any possible trap-placement effect. The locations of the traps were regularly changed throughout the infested areas once every month. The number of borers captured, temperature, relative humidity, and wind velocity were recorded each time a trap was emptied. Trapping continued for three months.

Effect of shade on trap capture efficiency Ramp traps baited with pheromone lures were placed in the shade and in sunlight at each of the four locations listed above about 5 m apart on the ground in banana plantations. The location and direction of the traps were regularly changed throughout the experimental areas once every month. Each treatment was replicated four times at each village and trapping continued for three months.

Population trend of Cosmopolites sordidus Monitoring was conducted on banana plantations in Guam for one year. At each location, a pheromone-baited ramp trap was set up, in the shade of banana trees. The traps were checked weekly, captured borers were removed and counted, and soapy water was added as needed. The locations and directions of the traps were regularly changed throughout the experimental areas once every month. Data on the daily temperature, relative humidity, wind velocity, and rainfall during the experiment were obtained from the National Weather Service Forecast Office, Tiyan (Guam) for the analysis.