BLOG POSTS ARE PRELIMINARY MATERIALS CIRCULATED TO STIMULATE DISCUSSION AND CRITICAL COMMENT. THE VIEWS EXPRESSED ARE THOSE OF THE INDIVIDUAL AUTHORS. WHILE BLOG POSTS BENEFIT FROM ACTIVE UHERO DISCUSSION, THEY HAVE NOT UNDERGONE FORMAL ACADEMIC PEER REVIEW.
By Conrad Newfield, Christopher Wada, and Kimberly Burnett
Growing Threats to Hawaiʻi’s Forests and Industries
Hawaiʻi’s native ecosystems and agricultural economy are under threat from invasive species. Each year, an average of 20 alien insects and 100 alien plant species arrive in the islands. This long and growing list of invasive species undermines the ecological, cultural, and economic foundation of Hawaiʻi. Farmers face mounting production costs. Communities lose ecosystem services from degraded forests and watersheds. And conservation managers struggle to keep pace with the speed of spread and damage.
In a recent UHERO report, we examined three pests: the coffee berry borer (CBB), erythrina gall wasp (EGW), and fireweed. Each threatens a key sector or resource: Hawaiʻi’s premium coffee industry, dryland forests and cultural heritage, and the cattle industry. In partnership with the Hawaiʻi Invasive Species Council, UHERO conducted an economic analysis of biological control (biocontrol) interventions against these pests. Our goal was to assess the return on investment (ROI) of these programs—asking whether the costs of research and release are outweighed by long-term ecological, cultural, and economic benefits. We find compelling evidence that biological control—the introduction of natural enemies to suppress invasive pests—delivers exceptional returns on investment while offering a sustainable, long-term solution for invasive species management.
Figure 1. Himalayan ginger invading native forests of Waikamoi, Maui. Photo credit: Seth Ruter
Biological Control as a Tool for Hawaiʻi
Biocontrols have been used to protect Hawaiʻi’s agricultural industry for over a century. The Hawaiʻi Sugar Planters Association, for example, funded decades of research, making the islands, at one point in time, one of the world’s best biocontrol centers. It also established inspection stations on Midway and Kiribati in the 1930’s, to prevent the spread of pests to Hawaiʻi from other sugarcane industries. Due to this combination of biocontrol research and previously adequate quarantine, Hawaiʻi is unique in the world in that it does not use pesticides for sugarcane.
Unlike chemical control, which requires repeated applications and can harm non-target species, or mechanical removal, which is labor intensive and costly, biocontrol agents can establish self-sustaining populations, providing long-term suppression at relatively low ongoing cost.
While some early biocontrol efforts produced notable and famous unintended consequences, there have been no recorded nontarget effects of biocontrol introduced after 1967 in Hawaiʻi. Modern programs are guided by rigorous safety protocols, with extensive host-specificity testing to ensure agents target only the intended pest.
The extensive economic benefits of biological control have been quantified elsewhere around the world, yet no work of this nature has been demonstrated locally. Our findings fill this gap, quantifying the return on investment for biocontrol here in Hawaiʻi.
Coffee Berry Borer (CBB)
Figure 2. Coffee cherry infested with CBB in Hawai‘i. Source: KISC.
Hawaiʻi-grown coffee commands some of the highest prices in the world, but profitability is undercut by CBB, an invasive beetle first detected on the Big Island in 2010. The beetle bores into coffee cherries, destroying beans and reducing yields.
Current management involves costly sanitation practices and frequent applications of Beauveria bassiana, a fungus that infects CBB. On average, farmers apply fungal sprays five times per season at a cost of nearly $200 per acre, with 85% of the state’s 7,300 coffee acres receiving treatment. Current CBB management practices represent a significant burden on farm profitability, with spray costs alone estimated at 5-12% of profits.
We model scenarios under which the biocontrol for CBB, Phymastichus coffea, has varying effectiveness. Under the baseline scenario—where biocontrol fully replaces current management practices—the program delivers a staggering $141.6 million in net present value with a benefit-cost ratio of 42.0. Even under highly conservative assumptions where the biocontrol agent achieves only 25% effectiveness compared to current management, the program still generates $32.8 million in net benefits and a benefit-cost ratio of 10.5.
These remarkable returns reflect the substantial costs that coffee farmers currently bear to manage CBB. Over 50 years, the investment generates benefits ranging from $36.3 million to $145.0 million, with a breakeven point at 1-2 years after release, marking the point when economic returns first outweigh the costs. The long-term economic benefits of CBB biocontrol vastly outweigh the upfront investment, with major implications for sustaining Hawaiʻi’s coffee industry against a pest that otherwise demands regular, costly control. At the time of writing, this agent has not been released.
Table 1. Present value cost, present value benefit, net present value, and benefit-cost ratio for the CBB biocontrol agent P. coffea
| Baseline | 50% Benefits | 25% Benefits | |
| Discount rate | 0.02 | 0.02 | 0.02 |
| Present value cost | $3,455,519 | $3,455,519 | $3,455,519 |
| Present value benefit | $145,015,606 | $72,507,803 | $36,253,902 |
| Net present value | $141,560,087 | $69,052,284 | $32,798,383 |
| Benefit-cost ratio | 42.0 | 21.0 | 10.5 |
Figure 3. Cumulative benefits vs. cumulative costs of P. coffea over 50 years
Erythrina Gall Wasp (EGW)
Figure 4. Large wiliwili tree at the Waikōloa Dry Forest Preserve. Photo credit: Conrad Newfield
The arrival of EGW in 2005 devastated Hawaiʻi’s dryland forests. Wiliwili (Erythrina sandwicensis), a culturally and ecologically significant tree, and other non-native ornamental Erythrina species were rapidly killed across the islands. Beyond ecological loss, the dieback threatened traditional cultural practices and community-based restoration efforts.
The initial release of Eurytoma erythrinae in late 2008 showed remarkable results—by 2011, 90% of sampled wiliwili trees had recovered full canopies, compared to widespread mortality in the initial years following the gall wasp invasion. A second agent, Aprostocetus nitens, is being considered for release to strengthen suppression for isolated wiliwili trees.
For the EGW biocontrol program, we estimate a lower bound of $27.2 million in benefits generated over 50 years, yielding a benefit-cost ratio of 24.0. Wiliwili’s cultural significance extends far beyond monetary measures. The tree appears in the Hawaiian creation chant, the Kumulipo, and provided essential materials for traditional practices including construction of outrigger canoes, surfboards, and fishing implements. The decline of wiliwili populations due to gall wasp damage demonstrably affected these cultural practices, along with affecting already-degraded lowland ecosystems. The biocontrol program’s success in preventing wiliwili extinction represents a significant success in the protection of Hawaiian culture and native forests.
Table 2. Present value cost, present value benefit, net present value, and benefit-cost ratio for the EGW biocontrol agents E. erythrinae and A. nitens.
| Baseline | |
| Discount rate | 0.02 |
| Present value cost | $1,100,000 |
| Present value benefit | $27,200,000 |
| Net present value | $26,000,000 |
| Benefit-cost ratio | 24.0 |
Figure 5. Cumulative benefits vs. cumulative costs of E. erythrinae and A. nitens over 50 years
Fireweed
Figure 6. Fireweed flowering in pastures in Maui, Hawai‘i, image by Forest & Kim Starr.
Fireweed (Senecio madagascariensis) spread rapidly across Hawaiʻi’s rangelands, significantly reducing the available area for forage. Ranchers have faced stark trade-offs: invest in costly herbicides, reduce stocking rates, adjust grazing patterns, or risk cattle losses.
In 2012, the fireweed moth (Secusio extensa) was introduced. Results have been mixed, with greater impacts observed in some areas than others, but economic analysis suggests substantial long-term benefits. Total biocontrol program costs of $2.5 million generate benefits ranging from $5.2 million to $23.8 million over 50 years, resulting in benefit-cost ratios between 2.0 and 9.2.
Although less dramatic than the results for CBB or EGW, the fireweed case illustrates how even partial suppression through biocontrol can be cost-effective.
Table 3. Present value cost, present value benefit, net present value, and benefit-cost ratio for the Fireweed biocontrol agent Secusio
| Avoided Management Costs (low) | Avoided Management Costs (high) | Avoided Cattle Losses (low) | Avoided Cattle Losses (high) | |
| Discount rate | 0.02 | 0.02 | 0.02 | 0.02 |
| Present value cost | $2,507,760 | $2,507,760 | $2,507,760 | $2,507,760 |
| Present value benefit | $5,213,079 | $10,426,159 | $8,936,348 | $23,830,261 |
| Net present value | $2,613,650 | $7,826,730 | $6,336,918 | $21,230,831 |
| Benefit-cost ratio | 2.0 | 4.0 | 3.4 | 9.2 |
Figure 7. Cumulative benefits (Low Avoided Management Costs scenario & High Avoided Cattle Damage scenario) vs. cumulative costs of Secusio over 50 years
Strong Returns
Across all three case studies, we find that biocontrol delivers net positive economic returns, even when accounting for the research, testing, and release costs. Cost-benefit ratios range from 2 to over 40.
Perhaps more importantly, benefits accumulate over time. Once established, biocontrol agents continue to provide pest suppression at little, if any, ongoing cost, freeing land managers and farmers from perpetual cycles of spraying or manual control. This makes biocontrol a particularly attractive strategy for controlling spreading pests that would require exponentially rising costs to otherwise control.
Broader Benefits and Policy Implications
Our quantitative estimates focus on market-based benefits, but the full value of biocontrol extends beyond dollars. Protecting dryland forests helps sustain biodiversity and cultural practices. Supporting ranchers helps maintain open landscapes that reduce wildfire risk and erosion. Sustaining coffee farming preserves a key local industry with global recognition.
Given the accelerating threats from new invaders like the Coconut Rhinoceros Beetle (CRB) and entrenched weeds like Himalayan ginger, investments in biocontrol research and application appear not only justified, but urgent. The spread of CRB has decimated palm trees across the state, threatening a traditional food source, local agriculture, and critically endangered native palm species. Himalayan ginger, one of the most aggressive weeds in the state, is replacing vast tracts of native forest understory, forming dense thickets. Manual or herbicidal control of invasive species is costly, sometimes ineffective, and does not scale effectively. In Hawaiʻi, an estimated $1 million is spent annually in an attempt to control Himalayan ginger, on par with the total research cost of most biocontrol programs (DLNR, 2024). Some invasives have no known biocontrol options, like the coqui frog and little fire ant, which are currently spreading throughout the Koʻolau mountains at a pace potentially beyond that which can be controlled on a limited budget. Aggressive targeting of species that can be controlled through biological methods is necessary to free up critical resources for control of those that cannot.
Building capacity in Hawaiʻi for early detection, agent testing, and release will yield high returns for decades and centuries to come. Hawaiʻi was once a global leader in biological control. A return to this position will be critical for safeguarding local agriculture, preventing extinction of critically endangered species, and protecting our finest natural resources. In the face of expanding invasion from these three studied species along with a large suite of others, many without biological control potential, we are confronted with the unknown and potentially significant consequences of not investing in biocontrol.