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May 17, 2023

Earth Day 2023: Spreading the Tectococcus Love

Written by Kari Bogner, Botany Program Manager, Pulama Lanai. 

We recognize the proper use of the Hawaiian language including the ‘okina [‘], a glottal stop, and the kahakō [ō] or macron (e.g., in place names of Hawai‘i such as Lāna‘i). However, these have been omitted from this website for the best online experience for our visitors. We realize the importance and continue to use them outside of the online platform.

In honor of Earth Day 2023 (April 22), Pulama Lanai, The Adventure Park, and Sensei Retreat collaborated to spread the scale, Tectococcus ovatus, a biological control agent (“biocontrol”) for strawberry guava in and around Koloiki Trail and Koele during the month of April. These backyard field trips became an opportunity for different groups to work together, to enjoy some delicious guava fruit, to learn about conservation work on Lanai, and to have an open discussion about what is often still considered a “hot topic” item in the field of Conservation.

Although its fruits are enjoyed by many, strawberry guava (Psidium cattleyanum), or waiwi, is one of the worst invasive species in the world. In Hawaii, this guava species forms thick monotypic stands that outcompete native plant species from growing on multiple fronts. Individual trees can grow so tightly next to each other that they shield out the necessary light for other plant species to germinate and grow. Additionally, their leaves produce allelopathic compounds that inhibit the growth of other plant species. Healthy, diverse native forests are crucial to our way of life in Hawai‘i, allowing our aquifers to efficiently and effectively recharge. Native forests also support hundreds of native animal species from the Kamehameha butterfly (pulelehua) to the beautifully-spiraled tree snails (kahuli) to the Hawaiian petrels (uau).

Tectococcus ovatus is a type of scale insect that only utilizes strawberry guava as a host plant, and does not affect the large, yellow-fruited common guava (Psidium guajava) or other plant species. Once a young scale, known as a “crawler,” emerges from a mature guava leaf, it crawls onto the soft new growth (liko) of another guava branch before penetrating a young leaf and remaining under that leaf’s surface for the rest of its life cycle. Scales are sap-sucking insects and thrive on the necessary sugars and other nutrients that trees need to grow and reproduce. In the case of this biocontrol, once a strawberry guava tree becomes heavily infected over time with the scale, it produces less fruit, loses lots of leaves, and in some cases will die. All of these effects from the biocontrol inoculation help to reduce the spread of strawberry guava at the landscape level and opens up the canopy for native species, such as uluhe fern (e.g., Diacranopteris linearis), to grow and foster growth of other native plant species. After many years of laboratory and field trials by the U.S. Department of Agriculture, this scale was officially released as a biocontrol for strawberry guava in Hawai‘i in 2014 and 2015. Thanks to current and former Conservation staff on the island of Lanai, the scale is well-established along several areas of Munro Trail. Over the past couple of years, Pulama Lanai’s Conservation Department has been revamping efforts to spread the biocontrol to new areas of the mountain. Over the course of several weeks this April, Pulama Lanai Conservation Department and the Company’s Landscaping Department at Sensei Retreat along with the Adventure Park and Sensei Retreat staff deployed over 300 heavily-infected strawberry guava branches onto the new growth of healthy strawberry guava trees in the Koele area. Although it will take several years for these inoculation events in the Koele area to meet a critical threshold that will cause dieback of the guava species, we are seeing the beneficial effects of this biocontrol eight years post-inoculation of waiwi on the mountain. We are seeing native uluhe fern making its way back into guava stands, and we are seeing lower fruit yield on trees. To be blunt, we are seeing a lot of very unhappy strawberry guava trees on Lanaihale. Currently, the best areas to collect heavily-infected strawberry guava branches on Lanai is a 30 minute UTV ride up Munro Trail. Having another hotspot to collect infected guava branches around Lanai City will facilitate more efficient inoculation of the healthy waiwi stands at lower elevations and hopefully bring conservation topics a little closer to everyone’s backyard on Lanai.

For more information about the biocontrol, Tectococcus ovatus, check out this online article:  https://storymaps.arcgis.com/stories/3100e2ca7f924fad9977e34ffa20df14

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