The wekiu bug, a flightless insect no larger than a grain of rice that lives atop Mauna Kea, can be hampered in dogma.
The wekiu bug, a flightless insect no larger than a grain of rice that lives atop Mauna Kea, can be hampered in dogma.
This member of the seed-feeding family of insects is touted for its ability to adapt to the harsh, cold and dry alpine conditions of the mountain’s upper reaches — an unusual location considering the daily temperature fluctuations, winter snow pack and virtual absence of plant life. One of the best known endemic insects to have evolved here, the wekiu bug also exhibits extreme specializations, both morphological and behavioral, which could be viewed as preposterous.
Foregoing the vegetarianism of its relatives, the wekiu bug is a carnivorous scavenger, eating dead and dying insects the wind carries upslope and deposits to its only known home, a cinder cone habitat above the 11,700-foot elevation. The natural antifreeze in their blood helps them to withstand freezing temperatures and snow while their long legs aid in scrambling over rocky terrain.
Still, very little has been learned about the bug’s life since its discovery in the 1980s. That is until two University of Hawaii entomologists — Jesse Eiben and Daniel Rubinoff — decided to study its life cycle and habitat.
What they found not only led to a better understanding of the habitat requirements, but also gave a reason for the wekiu bug’s persistence on cinder cone habitats, as well as how it’s able to survive and reproduce within the extreme environment. They also created a tool that could be used to make better conservation and management decisions pertaining to the bug and other insects of concern.
Eiben, an assistant professor at UH-Hilo’s College of Agriculture, Forestry and Natural Resources Management, and Rubinoff, a professor at UH-Manoa’s College of Tropical Agriculture and Human Resources, recently published an article, “Application of Agriculture-Developed Demographic Analysis for the Conservation of the Hawaiian Alpine Wekiu Bug,” in the journal Conservation Biology. The article describes how they were able to study and help conserve this rare insect using methods originally developed to track and control agricultural pests.
The wekiu bug is important because it’s an indicator species, meaning it serves as a measure of the environmental conditions that exist on the summit’s cinder cones, some of which have been altered for telescope facility construction. Endemic to the summit of just one volcanic mountain in Hawaii, the wekiu bug is also rare and faces several threats, including habitat degradation caused by human disturbance, invasive species and climate change.
“Understanding how habitat conditions affect population growth is essential for informed management decisions,” the article states. “Yet, due to the bug’s rarity, secretive nature, and harsh environmental conditions on the mountain, assessing the status of wekiu bug populations through direct observation is impractical.”
A solution Eiben and Rubinoff found to getting the information necessary is to use life tables and heat energy accumulation models, common tools used for modeling population growth and management of insect pests. Eiben said he got the idea to use life tables in an entomology class in 2002 and was surprised to learn this bookkeeping-like approach had not been used more for nonpest insects. Life tables were originally created to study pests, so farmers would be able to apply insecticides at the optimal time of day and during the correct growth stage on the host plant.
Eiben and Rubinoff believe life tables and heat energy accumulation models combined are the perfect tool for studying cryptic species because researchers can optimize their field monitoring methods and timing by searching for the concerned species in places and at times that match the bugs’ preferred conditions.
Besides guiding population monitoring efforts, Eiben said their tool for the wekiu bug coincides with breeding seasons and helps explain observed periods of maximum or minimum abundance.
Their study was also part of the research that contributed to the U.S. Fish and Wildlife Service deciding to remove the wekiu bug from the candidate listing for federal protection under the Endangered Species Act because a stable population was indicated. The bug has been caught in the tug-of-war over astronomy development of Mauna Kea since a petition to list it as threatened or endangered was filed in 2003.
Possessing the proper permits, Rubinoff and Eiben collected wekiu bugs near the summit. They used data sensors and loggers to record temperatures the insects experienced at the rock surface and below it, as well as made detailed bug behavior observations during field trips.
Back at UH-Manoa, Eiben, then a doctorate student, and Rubinoff, his adviser, started a captive breeding program with a laboratory colony of 30 wekiu bugs in 2007. That colony was supplemented with 20 to 30 wild bugs caught four times over two years.
The colonies were reared in three refrigerator-like chambers, with scheduled temperature regimes and manipulations. Besides being fed, the bugs were monitored eight to 10 hours a day. Student assistants Abby Mason, Oska Lawrence and Celeste Yee were key in helping Eiben and Rubinoff look after the bugs — a population which grew to 1,000 at one point, Eiben said.
Eiben and Rubinoff developed life tables to observe the bugs in the lab, discovering at what temperatures the insects grow best, and then finding those temperatures in their native environment. With the predictions created by raising the wekiu bug in captivity at various temperatures over the course of three years, they have created a predictive model to monitor the growth of the wekiu bug in its natural habitat and in areas being restored for population establishment.
Throughout their study, Eiben said they debunked myths like wekiu bugs could be killed by the heat of a hand holding them. They also discovered wekiu bugs are “habitat specialists” who must “actively thermo-regulate to maintain body temperatures within its functional limits to develop, reproduce and survive.” They use the cinder cone rock because of the thermal buffer it provides.
Thermo-regulation, the changing of exposure to environmental conditions, is not unusual in the insect world. Many insects do it to survive in a place that would be otherwise fatal, Eiben said. With the wekiu bug, thermo-regulation is restricted to the cinder cone habitat, which comprises only 12 square kilometers in their elevation range. Disturbance to this limited habitat can cause impacts and the future of the wekiu bug is still uncertain, which is why this tool is important in helping officials continue monitoring and protecting this species, Eiben added.
To view the article, go to onlinelibrary.wiley.com/enhanced/doi/10.1111/cobi.12315.