diaphorina citri

diaphorina citri Kuwayama, known as the Asian citrus psyllid, is a small insect measuring just 3-4 millimeters in length that represents one of the greatest phytosanitary threats to citrus farming.

Taxonomic classification:

• Order: Hemiptera

• Family: Liviidae (formerly Psyllidae)

• Genre: Diaphorin

• Species: citrus Kuwayama, 1908

Originating from Southeast Asia, this hemipteran has transcended its natural geographical boundaries and has established itself as one of the most devastating pests in global citrus farming. Not only because of the direct damage caused by its diet, but mainly because of its ability to transmit the bacteria Candidatus Liberibacter asiaticus, which causes huanglongbing disease (HLB).

Biological and morphological characterization

diaphorina citri presents biological characteristics that explain its success as an invasive pest.

Morphologically, adults are grayish-brown in color with irregular dark spots on their transparent wings, which are held in a "roof" shape over the body during rest.

This characteristic posture, combined with its tiny size, often makes it difficult to detect it early in the field, contributing to its silent establishment in new areas.

The insect's life cycle is relatively short, ranging from 15 to 47 days depending on environmental conditions, with an optimum temperature between 25-28°C. This rapid development allows multiple annual generations, resulting in rapid population growth. Females, capable of laying between 300 and 800 eggs during their lifetime, show a notable preference for young shoots of plants of the Rutaceae family, where they insert their eggs between flower buds or at the base of tender leaves.

The eating behavior of diaphorina citri is particularly relevant to understanding its importance as a vector of pathogens.

As a sucking insect, it uses its stylet mouthparts to pierce plant tissue and access the phloem, remaining in the same feeding site for hours. During this process, saliva containing digestive enzymes is inoculated and, if the insect is infected, the bacteria that cause HLB.

Etiology and global spread

The Asian origin of diaphorina citri and its subsequent worldwide dispersion perfectly illustrate the challenges imposed by globalization in the phytosanitary context.

Initially restricted to the tropical and subtropical regions of Asia, where it co-evolved with its natural hosts and natural enemies, the species found in international trade routes the means for its global dispersal.

Trade in infected citrus seedlings, passive transport in vehicles and plant materials, and natural dispersal through wind currents are the main factors responsible for its current distribution.

The absence of effective quarantine barriers during the initial decades of its dispersal contributed significantly to its establishment on new continents.

Currently, the pest is present in practically all citrus-growing regions of the world, demonstrating a remarkable capacity to adapt to different climatic conditions and production systems.

The damage complex

The damage caused by diaphorina citri can be categorized as direct and indirect, the latter being of incomparably greater magnitude.

Direct damage resulting from insect feeding includes yellowing and deformation of young leaves, general weakening of the plant and production of honeydew, a sugary substance that promotes the development of sooty mold. Although these symptoms are visible and can affect plant development, they rarely cause significant economic losses on their own.

The true devastating impact of diaphorina citri lies in its ability to transmit bacteria Candidatus Liberibacter, which cause Huanglongbing. This disease, also known as citrus greening, represents one of the most serious threats to the world's citrus industry.

HLB causes progressive symptoms that include asymmetrical mottling of leaves, small and deformed fruits, progressive decline of the plant and eventual death in 5 to 10 years.

The efficiency of diaphorina citri as a vector is of particular concern due to the propagative nature of transmission, where the bacteria multiply inside the insect and persist throughout its life.

Once infected, the insect becomes capable of transmitting the pathogen to healthy plants indefinitely, transforming each individual into a mobile unit for spreading the disease.

economic impacts

The economic consequences of the presence of diaphorina citri in the global citrus industry are alarming. In addition to the direct costs related to loss of production, the presence of the pest imposes significant additional costs on the production system.

The number of insecticide applications has increased from 6-8 to 20-30 sprays per year in many regions, representing a 300-500% increase in pesticide costs.

The need to exclusively use certified seedlings produced in protected nurseries also substantially increased the costs of establishing and renewing orchards.

Integrated control and management strategies

The control of diaphorina citri represents one of the greatest challenges in contemporary agricultural entomology, requiring integrated approaches that combine multiple management tactics.

The complexity of the problem makes any strategy based on a single method inadequate, requiring the coordinated implementation of cultural practices, biological control, chemical control and regulatory measures.

Cultural control plays a fundamental role through the adoption of nurseries protected with anti-aphid screens, elimination of alternative hosts such as Murraya paniculata, and appropriate silvicultural practices. The production of seedlings in a protected environment has become mandatory in many countries, representing a paradigmatic change in citrus farming.

Biological control, although promising, faces limitations related to the effectiveness and establishment time of control agents. The parasitoid tamarixia radiata has demonstrated satisfactory results in some regions, with parasitism of 60-80% of nymphs, but its isolated action is not sufficient to keep pest populations below the threshold of economic damage.

Chemical control remains the main immediate management tool, but faces increasing challenges related to the development of resistance, environmental impacts and high costs. Rotation of active ingredients and application of systemic insecticides via the root system emerge as important strategies to maximize efficacy and minimize negative impacts.

Regulatory and quarantine measures are becoming increasingly important, especially in regions that are still free of the pest. Early detection programs, control of the movement of plant material and compulsory elimination of infected plants are essential tools to delay the spread and establishment of the pest in new areas.

Click here to see the insecticides used against diaphorina citri