Years ago, many trees on island, including the popular flame trees, were blanketed by scarlet gourd vines that eventually killed its host by depriving it of sunlight.
In the last few weeks, it was observed that the invasive vines are hardly seen in the areas where they are usually found.
According to CNMI forester Vice Deleon Guerrero, although the dry season has also something to do with the vines’ demise, the biological control measures put in place have also been effective.
3 species
The biological means of controlling the scarlet gourd involve three species of insects.
They are the Acythopeus cocciniae or leaf mining weevil, the Acythopeus bukhartorum or gall weevil, and the Militia Oedipus or stem borer.
In collaboration with the Department of Lands and Natural Resources, Northern Marianas College-Cooperative Research Education and Extension Service released the three insects in five different locations on Saipan.
Led by then CNMI entomologist Jack Tenorio, DLNR and NMC-CREES allowed the insects to live and breed in the vines.
Deleon Guerrero recalled that the first insect that was released was the leaf mining weevil.
In the following months, the gall weevil was released to other locations.
There were some factors that didn’t allow the first two insects to quickly control the scarlet gourd, prompting the team to release the third one — the stem borer.
Thriving
According to Deleon Guerrero, Dr. Rangaswamy Muniappan of the University of Guam’s Agriculture Department and Life Science was the first entomologist contracted by CNMI Forestry under DLNR to search for a biological means to control the scarlet gourd or Coccinia grandis.
Muniappan conducted the “specificity testing” on mining weevil and gall weevil and was able to get approval from the U.S. Department of Agriculture.
When Muniappan moved to Virginia, he was succeeded by Dr. Gadi Reddy who continued the work with Tenorio.
Deleon Guerrero said the mining weevil and the stem borer are still thriving on island. But the gall weevil failed to establish itself, and this may be due to the abundance of its natural predators.
Under control
NMC-CREES said the island’s scarlet gourd problem is now under control thanks to the insects.
The scarlet gourd weevil feeds on the leaves of the scarlet gourd. Its larvae mine the leaves, causing even more damage.
Without leaves, the invasive vine will eventually die.
The stem borer lays eggs into the stems of the scarlet gourd and its larvae feed on the inside of the stem and grow into moths.
Both insects, according to Deleon Guerrero, target specifically the scarlet gourd and will not attack other plants. Once the population of the scarlet gourd is reduced, the number of insects that feed on it will also decline.
Deleon Guerrero said the last time they monitored the locations, there was significant progress observed.
The population of the stem borer and mine weevil has expanded, freeing the trees from the thick crawling vines and leaves of the scarlet gourd.
Positive
NMC-CREES said the results of all studies and researches have been very positive.
The scarlet gourd’s extensive leaf damage showed that the weevil is well established on Saipan.
Boreholes on many scarlet gourd stems showed that the moth is also doing well.
The scientists were able to find live larvae and pupae of moth and continued research is being done through the NMC-CREES entomology lab for rearing of additional moths.
It was concluded that the scarlet gourd retreated by about 30 to 50 percent since the release of the insects, making Muniappan and Reddy confident that the population of the scarlet gourd will be further reduced over the next couple of years.
NMC-CREES Director Ross S. Manglona thanked them as he stressed the importance of the hard work that went into the efforts against the scarlet gourd.
NMC interim President Lorraine T. Cabrera, for her part, said: “We are grateful to be able to work with, and in partnership with, such esteemed scientists and for the efforts of our hardworking staff at NMC-CREES.”
