Anoplophora chinensis, the citrus long-horned beetle (also appearing in many sources as Anoplophora malasiaca), is a long-horned beetle native to Japan, China, Korea, Taiwan and Southeast Asia where it is considered a serious pest. This beetle has invaded several countries in Europe, including Italy, Switzerland, Turkey, France, Germany, and Croatia. However, this beetle is characterized as an invasive species in many parts of the world, including countries in Europe such as Italy, as it has been able to be transported to additional geographic regions by burrowing into shipments from Asia to countries in Europe. The beetle was later discovered in August of 2001, at a Tukwila, Washington nursery near Seattle in a shipment from Korea of 369 bonsai maple trees. Three of the beetles were captured at the nursery, including a mated female ready to lay eggs. However, when the bonsai trees were dissected, eight larvae exit tunnels were found, indicating that five more might have escaped into the surrounding community. Officials concerned with the potential for spread asked residents in the region not to move firewood, even in areas with no known infestations.

Habitat

A. chinensis generally prefer warm, temperate climates, but not climates that tend to be too hot. Areas around the world known for temperate climates are more likely to be populated by a subspecies of A. chinensis as an invasive species. For example, the temperate climates of the US states Florida and California are likely more at risk for an infestation than other US states. In China, the preferred temperatures are approximately 3 °C-7 °C lower than another subspecies in Italy for optimal growth and development. The exact range of preferred temperatures can also vary depending on the population of 'A. chinensis' in a given region or country. A. chinensis is likely composed of two subspecies, with the other subspecies being Anoplophora malasiaca. A study showed that this subspecies of A. chinensis in China preferred temperatures approximately 3 °C-7 °C lower than a population of A. chinensis in Italy for optimal growth and development.

Temperatures are generally more stable in the roots of plants throughout the day as well as throughout the year, and this absence of drastic fluctuations in temperature allow for more of the offspring to pupate and grow into adulthood. Upon developing through all the instars of the larval stage, they then transition to the pupal stage, where they remain for 4-6 weeks. Once citrus long-horned beetles reach the adult stage, they are classified as pre-adults and take about 1-2 weeks to mature. The adult beetles feed on twigs, petioles, and leaf veins for 10-15 days before oviposition.

Reproduction

Citrus long-horned beetles find mates using contact and short-range pheromones. The host plant for larvae is important for determining longevity and fecundity of adults.

Genomics

A chromosome-level genome assembly of the citrus long-horned beetle (Anoplophora malasiaca) was published in 2026. The genome size is approximately 708 Mb, with 95.2% of the assembly anchored to 15 chromosomes. The assembly has a BUSCO completeness of 99.7%, and 23,515 protein-coding genes were predicted.

Parasitic behaviors

Anoplophora chinensis lays its eggs within the roots and vascular system of their host plant. The eggs hatch and spend their larval and pupation stages in the plant vascular system. This infestation damages the host plant, causing it to weaken and eventually die. This parasitism is a main reason that this species' transportation to other countries is commonly referred to as an infestation. Given that A. chinensis often inhabit citrus plants, these plants are most negatively impacted by this beetle's parasitism.

Given the current climate change crisis, the infestation of these beetles has economic implications for many countries, particularly where Anoplophora chinensis is invasive.

As an invasive species in Europe

The citrus long-horned beetle has been further implicated in parasitic behavior as seen in their disruption of the vascular tissue of trees. Researchers in one study collected several adult and larval citrus long-horned beetles from which molecular analyses and physiological traits could be measured. Amplification of specific sequences of the citrus long-horned beetle genome using the polymerase chain reaction confirmed that infestations within wooden tissue in plants was indeed citrus long-horned beetles. In doing so, they proved that DNA extraction from citrus long-horned beetles is a possible mechanism by which researchers can manage invasive beetle outbreaks. Through an analysis of larval frass collected in field studies, researchers can now reliably diagnose citrus long-horned beetle infestation, which can help in the inspections of plants for plant trading as well as facilitate more effective plant management techniques.

In Croatia in 2007, exit holes in Lagerstroemia and Acer palmatum in greenhouses indicated an invasion by Citrus long-horned beetles. A quarantine was enacted on these plants following this discovery and infested plants were burned. Plants that contained larvae were destroyed and up until 2010, the movement of plants in the nursery was prohibited. Croatia's status in eradicating these beetles is transient.

Impact on mating

The mating processes of Anoplophora chinensis depend primarily on pheromone secretion and reception, with very little dependence on visual cues. As with the general odorant receptors and ionotropic receptors, research suggests that all pheromones that are secreted during mate location as well as the mating process itself are generally short range.

While the female receptors are located within the female's cuticles, the male receptors are located on the male's antennae. In 1998 Qiao Wang at the Massey University Institute of Natural Resources demonstrated that these pheromones are most active between male and female beetles, as males did not detect any freshly dead male beetle until the male was physically touching it with his antennae, but he could detect a freshly dead female via pheromone reception. While searching for a mate involves receptors that receive signals from a short distance, mating behaviors themselves are enforced mostly by contact pheromones, with some reception of short-range volatile sex pheromones.

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File:Anoplophora malasiaca-2.JPG|Male, in Japan

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References

  • EPPO pdf
  • DEFRA/CSL and Forestry Commission UK Publication
  • COMMISSION DECISION on emergency measures to prevent the introduction into and the spread within the Community of Anoplophora chinensis (Forster) pdf
  • Species Profile- Citrus Longhorned Beetle (Anoplophora chinensis), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Citrus Longhorned Beetle.
  • Neue Westfälische from 3 July 2008
  • Defra News release 14 August 2008