Erythrina gall wasp becomes a new pest of ornamental plants, creating galls on trees that look like tumors
Erythrina gall wasp
The leaves of diseased Erythrina trees are covered with many small bumps, which are actually galls, each containing Erythrina gall wasp larvae inside.
It is a tiny wasp, so small that the human eye can barely see it; it is a ruthless invader, skilled at using "disfigurement" to mercilessly destroy flowers; it is a new face in the animal kingdom, and its origins remain a mystery. It is the "rising star" of biological invasions, the Erythrina gall wasp, currently spreading at a wildfire-like pace across many countries and regions, and has been included in the third batch of the "List of Invasive Alien Species in China" published by the Ministry of Environmental Protection.
Confirming a new face among wasps
Humans can map the entire Earth, but to this day have not been able to fully count how many species exist on the planet. Every year, news and reports of newly discovered animal and plant species appear around the world. Among the list officially published and confirmed as new species in 2004, there is a tiny wasp named Erythrina gall wasp (EGW for short), known in China as the "Erythrina gall wasp." Dr. John La Salle of the Australian Biological Atlas (ALA) described this new species from specimens collected in Singapore, Mauritius, and Reunion, France.
The year after it was named, this tiny insect appeared in China, with Shenzhen being the first place it was found in the country. In July 2005, when the Shenzhen Entry-Exit Inspection and Quarantine Bureau was conducting a survey at the Sea Field Scenic Area, it found that several introduced and planted Erythrina trees were diseased, and two had already died. The leaves of the diseased Erythrina trees had many small bumps (scientifically called galls), which contained unknown small insects. After monitoring, they were preliminarily identified as Erythrina gall wasps. The quarantine bureau then sent samples to Zhejiang University and the Chinese Academy of Sciences for verification, and contacted Dr. John La Salle in Australia to obtain specimen data, ultimately confirming them as Erythrina gall wasps.
At the end of August 2005, the Ministry of Agriculture, the State Forestry Administration, and the General Administration of Quality Supervision, Inspection and Quarantine jointly issued an announcement, listing this insect as a quarantine pest for imported plants and a forestry quarantine pest in China, announcing a suspension of importing Erythrina plants, and requiring all localities to take emergency quarantine, control, and eradication measures. What methods does this tiny insect have that made relevant departments react so quickly as if facing a major enemy?
Creating galls on trees like tumors
The inconspicuousness of the Erythrina gall wasp stems from the fact that it poses no direct harm to humans and is much smaller than mosquitoes or flies. The largest, the female, is only 1.45-1.6 mm, and the smallest, the male, is only 1.0-1.15 mm. Under a microscope, it looks like a bee in shape. The larger, dark brown one with yellow spots is the female, and the smaller, pale yellow one is the male. It has four forms: egg, larva, pupa, and adult. One generation (the individual development cycle from the egg leaving the mother's body to the adult reaching sexual maturity and beginning to lay eggs) takes only 1 month.
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A new scourge of ornamental plants, the "Erythrina gall wasp," creates galls on trees like tumors
Erythrina gall wasp
The egg, larva, pupa, and adult forms of the Erythrina gall wasp. Source: University of Hawaii
The leaves of diseased Erythrina trees are covered with many small bumps, which are actually galls, each containing Erythrina gall wasp larvae inside.
China Landscape Web, October 9 news: It is a tiny wasp, so small that the human eye can barely see it; it is a ruthless invader, skilled at using "disfigurement" to mercilessly destroy flowers; it is a new face in the animal kingdom, and its origins remain a mystery. It is the "rising star" of biological invasions, the Erythrina gall wasp, currently spreading at a wildfire-like pace across many countries and regions, and has been included in the third batch of the "List of Invasive Alien Species in China" published by the Ministry of Environmental Protection.
Confirming a new face among wasps
Humans can map the entire Earth, but to this day have not been able to fully count how many species exist on the planet. Every year, news and reports of newly discovered animal and plant species appear around the world. Among the list officially published and confirmed as new species in 2004, there is a tiny wasp named Erythrina gall wasp (EGW for short), known in China as the "Erythrina gall wasp." Dr. John La Salle of the Australian Biological Atlas (ALA) described this new species from specimens collected in Singapore, Mauritius, and Reunion, France.
The year after it was named, this tiny insect appeared in China, with Shenzhen being the first place it was found in the country. In July 2005, when the Shenzhen Entry-Exit Inspection and Quarantine Bureau was conducting a survey at the Sea Field Scenic Area, it found that several introduced and planted Erythrina trees were diseased, and two had already died. The leaves of the diseased Erythrina trees had many small bumps (scientifically called galls), which contained unknown small insects. After monitoring, they were preliminarily identified as Erythrina gall wasps. The quarantine bureau then sent samples to Zhejiang University and the Chinese Academy of Sciences for verification, and contacted Dr. John La Salle in Australia to obtain specimen data, ultimately confirming them as Erythrina gall wasps.
At the end of August 2005, the Ministry of Agriculture, the State Forestry Administration, and the General Administration of Quality Supervision, Inspection and Quarantine jointly issued an announcement, listing this insect as a quarantine pest for imported plants and a forestry quarantine pest in China, announcing a suspension of importing Erythrina plants, and requiring all localities to take emergency quarantine, control, and eradication measures. What methods does this tiny insect have that made relevant departments react so quickly as if facing a major enemy?
Creating galls on trees like tumors
The inconspicuousness of the Erythrina gall wasp stems from the fact that it poses no direct harm to humans and is much smaller than mosquitoes or flies. The largest, the female, is only 1.45-1.6 mm, and the smallest, the male, is only 1.0-1.15 mm. Under a microscope, it looks like a bee in shape. The larger, dark brown one with yellow spots is the female, and the smaller, pale yellow one is the male. It has four forms: egg, larva, pupa, and adult. One generation (the individual development cycle from the egg leaving the mother's body to the adult reaching sexual maturity and beginning to lay eggs) takes only 1 month.
A simplified distribution map of the Erythrina gall wasp produced by the University of Florida; Africa may be its place of origin.
After pesticide treatment of Hawaiian Erythrina, the damage from the Erythrina gall wasp was significantly reduced.
Like many invasive organisms, the Erythrina gall wasp has strong reproductive capacity. Adults mate shortly after growing wings. Before laying eggs, the female uses her ovipositor to pierce the epidermis of the host (Erythrina plants) and lays eggs inside the epidermal tissue of new leaves, petioles, tender branches, or young buds. After the plump little larvae hatch, they reveal their ferocious side, feeding on the mesophyll tissue of ornamental plants. Some might say, how much can such a tiny insect eat even if it eats its fill?
The answer lies in the fact that the larvae not only eat plant mesophyll, they also deploy chemical weapons, secreting special substances to stimulate plant tissues, causing abnormal proliferation of mesophyll tissue and forming galls. Just as rapidly growing tumors in the human body absorb large amounts of nutrients from the body, galls also provide nutrients for larval growth and development. Galls contain thin-walled, nutrient-rich tissues and large amounts of vascular tissue, directly affecting the production and transport of plant nutrients. Scientists have observed that a gall often contains one or two larvae. Whether living alone or "sharing rent," the enclosed environment provided by the gall can be described as having food and drink, safe and comfortable. What suffers is the plant: its floral beauty is destroyed, branches wither due to lack of nutrients, and in severe cases, dry up and die.
After the larvae complete development inside the gall, they become pupae, and then adults crawl out of the gall. Although the Erythrina gall wasp has a short life cycle, its egg production of about 320 eggs at a time and multiple generations within 1 year make its family prosper, bringing great difficulty to management.
High recurrence rate Slow research progress
The Erythrina gall wasp's characteristics of being very small, having concealed living places, rapid generational turnover, huge population numbers, and fast spread make it easy for it to escape customs quarantine. Also because it was discovered late and is a newcomer on the invasive species list, research and reports on it from various sectors are very few. After severe Erythrina gall wasp damage occurred in China's Taiwan region in 2004, Taiwan's scientific research departments also only used a few words in some scientific literature, such as "the wasp has negative geotropism and phototaxis, does not like camphor odor, and has no obvious reaction to citronella oil (which has mosquito-repellent effects)," to describe the conclusions of their behavioral observations, all of which added difficulty to targeted management.
In the State Forestry Administration's emergency notice on eradicating the Erythrina gall wasp epidemic and carrying out monitoring and general survey work, it first required all localities to cut off introduction channels at the source, suspend approval of introduction of Erythrina plant seeds, seedlings, and other propagation materials from epidemic countries and regions (Mauritius, Reunion Island of France, Hawaii of the United States, Singapore, Taiwan Province of China), and temporarily stop issuing "Plant Quarantine Certificates" for the transport of Erythrina plants.
In 2005, Guangdong and other provinces and regions adopted measures for Erythrina plants where the epidemic had already occurred, completely removing 1-2 year old branches and destroying all branches and leaves. For severely affected trees, they were immediately felled and either destroyed on site or subjected to quarantine disinfestation treatment. Despite adopting such extraordinary management measures, in June 2006, during a re-inspection organized by relevant departments in Shenzhen, it was found that among about 8,000 Erythrina trees affected by the gall wasp the previous year, the recurrence rate was as high as over 60%, which was extremely troublesome.
In August 2014, in the "List of Invasive Alien Species in China (Third Batch)" jointly issued by the Ministry of Environmental Protection and the Chinese Academy of Sciences, the Erythrina gall wasp was listed as one of 18 invasive species. The Ministry of Environmental Protection recommended pruning the leaves and tender branches of trees where the Erythrina gall wasp is found, cleaning up galls and branches and leaves that have fallen to the ground, and centrally burning or burying the leaves and tender branches in pits to prevent spread. For newly occurring isolated epidemic points and plants, adopt felling and on-site destruction, and spray pesticides on Erythrina plants around the affected area for prevention. However, judging from 10 years of management experience, control of the Erythrina gall wasp is not optimistic.
A simplified distribution map of the Erythrina gall wasp produced by the University of Florida; Africa may be its place of origin.
Its origins remain a mystery
Over the past 10 years, the scientific community has traced the origins of the Erythrina gall wasp, but to date it still has not been clarified where its homeland is. Some scientific literature believes it "almost certainly came from East Africa." The Invasive Species Specialist Group (ISSG) analyzed data and situations on the appearance of the Erythrina gall wasp around the world and concluded that in mainland China, Hong Kong, China, Taiwan, China, India, Japan, the United States, Singapore, Mauritius, American Samoa, and other places, the Erythrina gall wasp shows invasiveness; in Vietnam, the Philippines, Malaysia, South Africa, Thailand, Tonga, the Maldives, Fiji, Guam, New Caledonia, the Federated States of Micronesia, Samoa, Reunion, and Vanuatu, its invasiveness is "not yet clear." This also indirectly shows that defining invasive species requires time for observation and corresponding technical means for identification.
In 2005, the Erythrina gall wasp was first discovered on Oahu in Hawaii, USA. Researchers found that this tiny insect was very harmful to the locally unique Hawaiian Erythrina, and within two years could cause 95% of local Erythrina trees to die. In 2008, Hawaii spent 1 million USD to manage the pest damage. The main management methods were removing pest-affected branches and leaves and applying pesticides, and also establishing 15 monitoring points for long-term observation. Materials from the University of Hawaii indicate that the Erythrina gall wasp has two natural enemies in Africa, but research on biological control of the Erythrina gall wasp has not progressed much, which shows how difficult it is to introduce natural enemies of invasive species.