Coconut Rhinoceros Beetle (CRB) is a large scarab beetle native to Southeast Asia that has spread across many Pacific islands. Adults are typically around 2 inches long and are easily recognized by the prominent horn on their head.

CRB primarily target palm trees, where adults bore into the crown and feed on the soft, developing tissue of emerging fronds (the growing spear). This feeding can cause significant damage to palms and, in severe cases, can weaken or kill the tree.

Coconut Rhinoceros Beetle (CRB) primarily feed on palms, with coconut palms being their preferred host. They bore into the crown of the tree and feed on the soft growing tissue of emerging fronds. While palms are their main food source, CRB will also attack other palm species when available.

In areas with high populations, such as parts of Oahu, CRB have also been observed feeding on or damaging non-palm plants, including hala and pineapple. These cases are less common, but they show that CRB can expand their feeding range when preferred hosts are limited or under heavy pressure. For a full list of hosts, click here.

Coconut Rhinoceros Beetle (CRB) damage is usually seen in newly emerging fronds because beetles bore into the growing spear of the palm. As these fronds unfurl, they often show a characteristic “V-cut” pattern. The edges of these cuts are typically smooth and scalloped (rounded half-moon shapes), which helps distinguish CRB damage from other causes.

This can be confused with rat or trimming damage. Rat damage is usually shredded or tattered, while trimming damage tends to be clean and straight. Another key sign of CRB activity is the presence of large bore holes—often around 2 inches wide—in the bases of fronds or the crown area, sometimes appearing as partial holes where two fronds split.

CRB damage is often not immediately visible, since it may take weeks to months for the affected fronds to grow and fully emerge before the damage can be seen.

How quickly Coconut Rhinoceros Beetle (CRB) will kill a palm varies, but in most cases it is a slow process that requires repeated damage over time. CRB typically feed by boring into the crown and fronds of coconut palms, and healthy trees can often tolerate some level of damage.

A palm is only killed if CRB damage reaches and destroys the growing point (the meristem or “palm heart”), which is where all new leaves are produced. When this happens, the tree cannot recover. The wounds created by boring can also leave the palm more vulnerable to secondary infections and other stress factors.

If a palm declines very quickly—such as rapid drooping, discoloration, or full crown collapse—it is more likely due to disease or another stress factor rather than CRB alone.

Coconut Rhinoceros Beetle (CRB), like all beetles, go through complete metamorphosis—similar to how a caterpillar becomes a butterfly. They develop from eggs into grubs (larvae), then pupae, and finally emerge as adult beetles. Once they become adults, they do not continue growing.

CRB grubs are typically found in compost, mulch, or other decaying plant material. They are pale white with a brown head capsule, starting very small but growing up to about 3 inches long. Many scarab beetle larvae look very similar, so careful identification is important.

If you find grubs that may resemble CRB, please place them in a container with some soil, take clear photos or videos, and report them to biisc@hawaii.edu for identification. Do not squish them before they can be confirmed!

Black panel traps used for the coconut rhinoceros beetle (CRB) are detection tools, not a control method. These traps are used to monitor where CRB are present and help track their spread over time, rather than reducing populations.

The pheromone lure inside the trap has a very limited attraction range, so it does not pull beetles in from distant areas or create new infestations. Instead, if a CRB is found in a trap, it indicates that the beetle was already present in the local area. This information helps guide response efforts, targeting, and early detection in affected regions.

The most common beetle confused with Coconut Rhinoceros Beetle (CRB) is the Oriental Flower Beetle (Oriental Flower Beetle). Adults are often seen flying during the day and may look similar in flight to other large beetles, while CRB are typically nocturnal and most active at night or around dusk.

Oriental Flower Beetles are usually dark brown with coppery speckling and do not have a horn, unlike CRB. The larvae (grubs) can look very similar, but there are key differences: OFB grubs have a visible raster pattern on the underside of the abdomen, a smaller head capsule, and can curl into a distinct “C” or “E” shape. CRB grubs lack a raster pattern, have a larger head capsule, and are generally bulkier.

Behavior can also help with identification. OFB larvae tend to be more active and can move quickly, often appearing to crawl upside down, while CRB larvae are slower and typically move on their side or in a more sluggish manner.

Tree injections used to manage CRB are designed to minimize environmental exposure compared to other application methods. Because the active ingredient is placed directly into the tree’s vascular system, the potential for drift or off-target movement is very low. Once absorbed, the compound is largely retained within the plant, and significant movement into soil or groundwater is considered unlikely under normal use conditions.

Some minor leakage can occur during the application process itself, but this is typically very limited and localized. Compared to foliar sprays or soil drenches, injections generally reduce environmental contact but require more labor and time, as application must match the tree’s uptake rate. In return, injections tend to provide longer-lasting protection, meaning treatments are needed less frequently.

Tree injections used for managing coconut rhinoceros beetle (CRB) have raised concerns about potential impacts on coconuts. In practice, trees selected for injection are ornamental or located in managed public areas where regular maintenance already requires removal of flowers, fronds, and nuts for safety, especially in high foot-traffic locations where falling debris can be a hazard. As a result, these trees are not typically used as a food source.

For coconut trees that are actively harvested for food, there are alternative management options that do not involve injections, including sanitation, trapping, and habitat reduction. These methods can help protect productive trees while still reducing CRB pressure in the area.

Evergreen Pyrethrum Concentrate (organic) are easily attainable by the homeowner and can be used on fruiting trees. This breaks down quickly in the environment. Best applied when you think there is active feeding going on. If you don’t want to use pesticides you can also use netting (½ inch – 1 inch holes). The netting needs to be wrapped around the crown and spear in multiple ‘fluffy’ layers. The net needs to be redone at least every 2 months as the spear grows out.

Using sand in the crown of palm trees has been practiced in some regions as a way to deter CRB, but it should not be relied on as a standalone solution. Adding sand can provide a physical barrier by filling gaps and spaces in the crown where adult beetles may enter and begin boring. The abrasive nature of sand may also make the crown a less favorable environment for beetle movement and activity. However, sand does not kill beetles, prevent all damage, or treat an active infestation. It also requires frequent reapplication, as rain can wash it away and new spear growth can push sand out of the crown over time. Effective CRB management depends on sanitation—especially removing and properly managing green waste—along with regular monitoring and coordinated control efforts.

There have been some studies evaluating the use of salt on CRB, with the most effective results seen when salt is applied to breeding materials such as decaying green waste rather than as a crown treatment. In higher concentrations (around five times recommended levels), salts such as Epsom salt have been shown to inhibit larval development and may deter females from laying eggs. However, applying salt at these levels can also make treated organic material unsuitable for use as soil amendment due to increased salinity. There is limited research on applying salt directly into palm crowns; at most, it may act as a deterrent rather than a lethal treatment. Like sand, salt will also gradually wash or fall out of the crown with rain and plant growth, requiring repeated applications. While coconut palms can tolerate some salt exposure, excessive salt in the soil can negatively impact soil health by reducing water and nutrient uptake and ultimately inhibiting plant growth.

Avoid stockpiling large piles of green waste, mulch, or palm debris for extended periods—ideally no longer than 3 few months—since these materials are perfect breeding habitat for CRB. Whenever possible, haul material to County green waste. If green waste must be stored temporarily, covering piles with netting (1/2″ eye) can help limit CRB from getting into the material.

Managing organic material is a key part of controlling CRB populations. Compost that is properly heat treated to kill CRB can become suitable breeding habitat as it starts to cool. Avoid long-term stockpiling of compost unless it is fully contained in a CRB-proof container, and aim to move or use material within a few months.

If you can’t contain the material, covering piles with netting (about 1/2–1-inch mesh) can help to reduce CRB access (make sure netting is loose and pillowy rather than tightly stretched over the material.

There is no best product for CRB control. The best thing to do is to implement an integrated pest management (IPM) plan. A little bit of everything. Both trees and green waste must be managed. Reduce the amount of breeding material and treat/net the trees.

There are a few biological control options for Coconut Rhinoceros Beetle (CRB), but the situation is complex because different CRB populations can respond differently depending on their region of origin. Some strains are more resistant to certain biological controls than others—for example, CRB populations from Guam are not affected by the Oryctes nudivirus that works against CRB in other Pacific countries.

Research institutions such as the University of Hawaiʻi (UH) have worked on importing and evaluating this virus for local use, but it is still in testing and not yet widely deployed. If approved and released, the virus would spread naturally through CRB populations.

A fungal pathogen has also been used in some regions as a biological control on breeding material, though it is generally considered less effective than the virus. Natural predators such as chickens, pigs, and mongoose may also consume CRB larvae, but their impact is limited by access. They are more likely to find larvae when breeding material is spread thin or in smaller piles, since large piles allow grubs to remain hidden deeper inside.