The Red Palm Weevil

The Red Palm Weevil: Identification and Control

The red palm weevil, also known as Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae), is a highly destructive pest of palm trees. Its ability to devastate palm populations can lead to significant economic, environmental, and social impacts when introduced to new regions.

Introduction to the Red Palm Weevil

The red palm weevil is the most significant pest affecting date palms (Phoenix dactylifera) worldwide and a serious threat to coconut palms (Cocos nucifera). Native to South Asia and Melanesia, this pest has rapidly expanded its range westward since the 1980s. It was first detected in Saudi Arabia and the United Arab Emirates in 1985 and has since spread across the Middle East.

By 1994, it was identified in Spain and other Mediterranean countries where major palm species, such as the date palm (Phoenix dactylifera) and the Canary Island palm (Phoenix canariensis), are cultivated or used ornamentally. Reports also indicate attacks on other ornamental palms, like the Chusan palm (Trachycarpus fortunei). The severity of its damage in the Mediterranean led the European Commission to implement emergency measures to curb the spread of R. ferrugineus.

Geographic Distribution

The red palm weevil has been reported in most regions where date or ornamental palms are grown, with the highest damage recorded in:

• Southeast Asia: Thailand, Taiwan, Cambodia, Philippines, Laos, Myanmar, Indonesia, Malaysia
• East Asia: China, Japan
• Oceania: Melanesia, Australia, Papua New Guinea, Solomon Islands, Vanuatu, Western Samoa
• Europe: Albania, Croatia, Cyprus, France, Greece, Italy, Malta, Portugal, Slovenia, Spain, Georgia
• West Asia: Saudi Arabia, UAE, Iraq, Kuwait, Yemen, Qatar, Oman, Iran, Jordan, Syria, Turkey, Lebanon, Bahrain, Israel
• South Asia: India, Pakistan, Bangladesh, Sri Lanka
• North Africa: Tunisia, Egypt, Morocco, Libya, Algeria
• Caribbean: Aruba, Curaçao, Netherlands Antilles
• Central America: United States, Mexico

Life Cycle of the Red Palm Weevil

Like many Coleoptera, the red palm weevil undergoes four main life stages: egg, larva, pupa, and adult. The adult weevil lives up to three months, during which it completes multiple mating and egg-laying cycles.

Egg

Female weevils lay eggs individually in holes drilled into the palm using their snout, which serves as an ovipositor. The eggs are creamy white, glossy, and rectangular, measuring approximately 2.62 × 1.12 mm (Menon & Pandalai, 1960).

Larva

Before hatching, the larva’s mouthparts are visible through the egg’s shell. Hatching occurs within 3 to several days, depending on temperature. Larvae are creamy white, legless, and pear-shaped, growing up to 50 mm long and 20 mm wide, with a reddish-brown to black head and 13 body segments. Larval development, influenced by diet and temperature, ranges from 24 to 128 days (Butani, 1975; Salama et al., 2009). The number of larval instars varies based on the host plant or diet, with reports ranging from 3 to 17 instars (Nirula, 1956; Martin & Cabello, 2006; Dembilio & Jacas, 2011). Newly hatched larvae bore into the palm, creating tunnels that cause significant damage, particularly to the soft tissues around the apical meristem. Mature larvae move toward the trunk’s periphery or crown to form a cocoon from palm fibers.

Pupa

The transition from larva to prepupa takes about three days (Viado & Bigornia, 1949). Prepupae then develop into pupae inside the cocoon (Murphy & Briscoe, 1999). Pupae, averaging 80 × 35 mm, are initially creamy white, turning brown, with a glossy, net-like surface (Murphy & Briscoe, 1999). The pupal stage lasts 11 to 45 days (Viado & Bigornia, 1949; Esteban-Durán et al., 1998a).

Adult

Adult red palm weevils are large, rust-red, and measure about 40 × 10 mm, with a long, curved snout comprising one-third of their body length. The dorsal thorax has dark spots, and males have short, brown hairs on the anterior half of the snout, while females have a hairless, narrower, and more curved snout. Adults are strong fliers, capable of traveling 500–800 meters (Wattanapongsiri, 1966b). Computer-assisted flight analysis shows 54% are short-distance fliers (<100 m), 36% cover medium distances (100–5,000 m), and 10% can fly over 5,000 m (Ávalos et al., 2014). Newly emerged adults may remain in the palm, consuming the meristem until the tree dies.

Damage Caused by the Red Palm Weevil

The weevil bores multiple tunnels into the palm’s trunk and offshoots. Females lay 200–500 eggs, and upon hatching, larvae feed on the palm’s young tissues for about a month until the larval stage ends. Egg-laying typically occurs at the base of young petioles or in the crown. Within three weeks of hatching, larvae can destroy significant portions of the palm’s leaves and young tissues. Crown rot, leaf drop, and drying are key signs of infestation. As the weevil operates inside the tree with minimal external signs until severe damage occurs, it is often called the “silent pest” of date palms.

Management and Control of the Red Palm Weevil

Maintaining farm hygiene, including removing potential overwintering sites, is critical for prevention. Severely infested palms should be destroyed by shredding, as burning live palm tissues is ineffective. Freshly cut or damaged palm surfaces must be treated with insecticides to eliminate volatile compounds that attract female weevils for egg-laying.

Trapping and Monitoring

Continuous monitoring is essential to protect palms from infestation (Faleiro, 2006; Rochat, 2006; Guarino et al., 2013; Vacas et al., 2013). Pheromone traps baited with food play a key role in controlling this pest. The primary pheromone, ferrugineol, combined with methyl-5-nonanone-4, is used for mass trapping (Hallett et al., 1993; Vacas et al., 2014; Abraham et al., 1998). These traps attract more females than males, typically at a 2:1 ratio (Oehlschlager, 1998; Vidyasagar et al., 2000). Jayanth et al. (2007) reported that 74% of trapped adults were females, which is critical for preventing new infestations. Standard four-window bucket traps (Faleiro, 2006) are widely used, often baited with food sources like palm tissue, dates, or sugarcane mixed in 1 liter of water (Hallett et al., 1999). Key considerations include:

• Replacing food bait weekly.
• Using fermented food with ethyl acetate to increase trap efficiency up to fivefold (Oehlschlager, 1998; Sebay, 2003; Al-Saoud, 2013).
• Placing traps in shaded areas to prevent degradation of active compounds.
• Using 1–10 traps per hectare, depending on infestation levels (El-Shafie et al., 2011).

Host Plant Resistance

Plant resistance mechanisms are classified as:

• Antibiosis: Interactions between the host and insect cause physiological or developmental disruptions in the pest.
• Antixenosis: The pest is repelled or not attracted to the host.
• Tolerance: The plant’s genetic makeup allows it to withstand pest damage (Kogan & Ortman, 1978; Wiseman, 1999; Ju et al., 2011).

Quarantine Treatments

Detecting early infestation is challenging (Nakash et al., 2000; Al-Shawaf et al., 2013). Combined chemical and physical treatments are key. Fumigants like phosphine (PH₃) are effective due to their high penetration and toxicity, though methyl bromide (CH₃Br) is banned under the Montreal Protocol for its ozone-depleting effects (MARM, 2014). Phosphine, at 1.14 g/m³ for three days, successfully eliminates all life stages of the weevil (Llácer & Jacas, 2010).

Warning: Phosphine is a highly toxic, colorless gas that poses risks to human respiratory and digestive systems, potentially causing fatal poisoning.

Chemical Control

In the 1970s, carbamate and organophosphate insecticides formed the basis of chemical control in India (Murphy & Briscoe, 1999). More recently, phenyl pyrazole and neonicotinoid insecticides, such as imidacloprid and thiamethoxam, are used for preventive and curative treatments (Hernandez-Marante et al., 2003; Dembilio et al., 2010a).

In Spain, eight preventive insecticide treatments per season (April to October) are recommended, using neonicotinoids (imidacloprid, thiamethoxam), avermectins (abamectin), and organophosphates (chlorpyrifos, phosmet) via crown sprays, trunk injections, or soil drenches (MARM, 2014). Imidacloprid is recommended at 5 ml per palm through irrigation in late winter to spring and post-harvest (Soroker et al., 2005). Abamectin injections cause 50–90% larval mortality within a month, while imidacloprid achieves over 90% mortality for over two months (Dembilio et al., 2015).

Warning: Insecticide injections must be supervised by trained personnel to avoid palm tissue damage.