Managing breeding sites is critical for preventing the spread of Oryctes rhinoceros (Coconut Rhinoceros Beetle)
Posted on Feb. 26, 2024 / Invasive Species, Nursery, Plant Pests, Golf Courses, Parks / Subscribe 0
By: Keith Weiser
Oryctes rhinoceros, the coconut rhinoceros beetle (CRB), is the greatest threat to palms in Hawai'i. CRB adults damage many palm types but some preferred genera include Cocos (niu, coconut), Phoenix (date), Elaeis (oil), Pritchardia, Washingtonia, Livistona, and Roystonea (royal). CRB will also damage banana, sugarcane, pineapple, hala, cycads, ferns, and other crops especially when preferred hosts are scarce. Loulu, native Pritchardia palms, are a preferred host and even populations at high elevations on Oʻahu are being impacted which is undermining efforts to prevent the extinction of some of these endemic species. Preliminary testing at the University of Hawaiʻi indicates that other native plants besides palms may also be damaged by CRB. CRB has had a devastating impact on most of Oʻahu, and without widespread intervention, it will impact every individual and business that owns, grows, sells, services, or transports host plants.
Figure 1. In palms, v-shaped cuts on palm fronds are some of the first damage to emerge after an adult beetle bores into a palm but v-cuts can appear from other damage to the palm like trimming, rats, and disease.
CRB was first found on O'ahu near Pearl Harbor in 2013 and spread slowly during the first six years. By 2019 CRB had established in central O'ahu and quickly spread to almost every part of the island. In 2023, CRB was found for the first time on Kaua'i, Hawai'i Island, and Maui. The vector for spread is not obvious in most cases, but the in-state transport of commonly infested materials has only been regulated recently with temporary interim rules active from July 2022 to June 2023 and October 2023 to October 2024. CRB life stages can be found in several commonly transported commodities; mulch, compost, and potting soil are favored materials for breeding. Potting soil in bags, planted pots, bulk shipments, and around the roots of plants can be infested. CRB adults bore into the crowns of host palms for several days to feed and can be accidentally transported. Tree stumps, decaying logs, and standing dead palms can also be infested, causing the accidental spread of CRB. Most of these products are difficult to inspect adequately because the CRB are buried in material or burrowed inside of the plant. The eggs are small and can be mistaken for some types of slow-release fertilizer.
Figure 2. CRB adult. Anything that is significantly larger than 1.5 inches is likely to be CRB.
Figure 2. CRB larvae are only a few millimeters when they hatch but 6-10 weeks after hatching they are larger than any other beetle larvae in Hawai'i. Anything that is significantly larger than 1.5 inches is likely to be CRB.
Figure 4. CRB eggs.
With the difficulty of inspection and incomplete restrictions on the transport of potentially infested materials, transport to new areas appears inevitable. Early detection of incipient populations is critical to slow the spread and potentially eradicate infestations in a new area. The first detection on Maui was made by an arborist removing standing dead coconut palms near a golf course and a green waste processor. The first find on Hawai'i Island was by a homeowner inspecting a decaying palm stump in their yard. The first find on O'ahu was in a trap near numerous large, irrigated mulch piles on a golf course. The first find on Kaua'i was in a trap at a green waste transfer station, however, populations were later found to be concentrated at a nearby golf course. There are several risk factors for establishment and proliferation in a new area. The import of high-risk material from an infested area is the greatest risk factor followed by the presence of host plants, significant volumes of breeding material, and moderate to high rainfall or irrigation. Sites that have all of these risk factors typically include golf courses, nurseries, farms, botanical gardens, green waste processors, green waste dump locations, and residential or commercial landscaping projects. Arborists and landscaping professionals work in these locations and devote a lot of attention to the plants and breeding material. As such, they can play a critical role in the prevention and early detection of incipient CRB populations.
The presence of CRB in a new county is determined by the collection of a specimen of any life stage that has been verified by the US Department of Agriculture. Identifying distinctive damage on host plants can guide surveys, but v-cuts on plants are not enough evidence to determine if an area is infested, especially if the plants were recently transported to the site. CRB damage can take months to emerge and be visible on the fronds.
Traps baited with pheromone are deployed at most ports across Hawai'i but there is insufficient funding to purchase and maintain traps to monitor the entire state. Traps are maintained in infested areas to assess the risk of transport, to measure the efficacy of treatments, and to gather data on population dynamics. Traps are less attractive than palms or breeding material and one experiment estimates that the traps used in Hawai'i catch 11% of beetles when deployed with 100-meter spacing between traps. This makes traps a poor management tool, but their easy deployment and maintenance makes them the best available option for large-scale detection and population tracking.
The highest populations on O'ahu and the most severe tree damage are correlated with an abundance of breeding material which is usually in the form of mulch or compost. This breeding material does not have to be on the same property as the affected plants. The flight range of CRB has not been fully established but CRB can probably fly over a mile if needed. It is most likely that CRB typically travel much shorter distances when transiting between breeding sites and host plants for feeding.
The most effective management tool is the removal of all decaying plant matter on a landscape scale. The only successful eradication of CRB in the world employed the removal of all breeding material from a small island in Tonga, and it took a decade of effort to be successful. This level of green waste management is not practical in many areas but large reductions in breeding material will result in lower populations and less host plant damage. This strategy worked well at the initial infestation on Oahu at Māmala Bay Golf Course. The infested and high-risk material was heat-treated and removed then a green waste management plan was adopted for Joint Base Pearl Harbor-Hickam that required all green waste to be either burned or chipped and removed. Māmala Bay had 795 trap finds in 2014 which dropped annually to 425, 121, 28, then to zero finds for 2018 and 2019. From 2020 through 2023 there was an average of about 5 finds per year. This level of green waste management requires collaboration of all landowners and managers in a large area and is not possible in natural areas like forests or with businesses that process and store large amounts of green waste.
Where removal is not possible, breeding material can be treated. The ideal treatments kill all CRB and include heat treatments that reach a core temperature of 131 degrees Fahrenheit or a uniform temperature of 115 degrees Fahrenheit, fumigation with sulfuryl fluoride, and chipping of whole waste. Container storage is ideal for treated material that is not removed. Storage in a fully sealed container that CRB cannot burrow through will prevent infestation of fresh or treated material. Submersion for 48 hours in water can kill larvae but the adults may survive. Other good but less impactful actions include spreading material as thinly as possible, grinding, sifting, periodic survey and removal of CRB, burial, tilling into the soil, grazing with animals that eat larvae, and regular turnover.
Treatment of host plants is complementary to green waste management and is the primary approach when breeding material cannot be adequately managed. Treatments have primarily been tested on coconut palms, but many will work on other hosts where allowed. Tested chemical treatments include trunk injections, soil drench, and crown sprays. Systemic application of imidacloprid (group 4a) and acephate, (group 1b) have been the most common applications in Hawai'i. More recently, applications of pyrethroids have yielded promising results in drone applications and application with sprayers from lifts and bucket trucks. The crown applications often result in beetles falling from the crown within minutes or hours of treatment which aids in detection. Injections and drenches can take weeks to before the chemicals accumulate in the crown but have a long residual effect. Care must be taken to remove inflorescences or apply in a manner that minimally impacts pollinators. Some treatments can only be used on ornamental palms. However, growing and harvesting fruit can often resume after a period of time as specified by the pesticide label. Physical barriers can be used to protect host plants with monofilament netting being the most popular choice. Netting is placed toward the base of the upper fronds and requires repositioning as new fronds emerge. Using the proper mesh size is critical for its effectiveness.
Each Hawaiian Island is in different stages of infestation. With the currently available tools and technologies, eradication on O'ahu is not feasible. However, efforts directed at reducing populations, especially at air and seaports are critical for containing this population and preventing additional spread to other islands and the US Mainland. Kaua'i is in the early stages of infestation, but the initial eradication efforts have been largely abandoned. Hawai'i Island and Maui have each had one small breeding site reported and several organizations are working to delimit and eradicate these incipient CRB populations. There have been no finds on any of the other Hawaiian Islands.
Keith Weiser, CRB Deputy of Operations, Coconut Rhinoceros Beetle Response-Hawaii.
0 Comments