Psyllids are small insects of the order Hemiptera that affect different types of plants, from fruit trees to vegetables. In this article we will explore in detail the life cycle of psyllids, the damage they cause, how to recognize them, their most important species, as well as the control measures and treatments available to combat them effectively.
### What are Psilas or jumping aphids? ###
Psyllids, also known as “jumping aphids,” are insects that feed on plant sap, causing damage that directly impacts plant productivity and development. Due to their small size and ease of propagation, they become a rapidly expanding pest under favorable conditions. Psyllids are usually found on the underside of leaves and on young shoots, areas rich in nutrients that facilitate their development.
### Life Cycle of Psilas ###
The life cycle of psylla includes three main stages:
Egg: Females lay eggs in young plant tissues, especially leaves and shoots. Depending on the species, eggs may vary in size and color.
Nymph: Upon hatching, nymphs go through several moults before becoming adults. During this stage, nymphs feed intensively on sap and produce honeydew, which serves as a substrate for the development of fungi such as sooty mold.
Adult: Adults have wings and can move between plants, dispersing the pest to other areas. In the adult phase, females and males have morphological differences that make them easily recognizable. Females have an elongated abdominal ending that allows them to lay eggs in cracks and tight places. In addition, females have reddish-orange eyes while males have brown eyes.
Under optimal conditions, psyllids can complete their cycle in just a few weeks, which encourages rapid reproduction. This cycle is repeated several times a year, especially in warm climates, allowing the pest to multiply rapidly.
### Damage Caused by Psilas ###
Aesthetic damage: Many psyllas produce a kind of cotton that affects the aesthetics of the plant and in severe cases can cover a large part of the leaves.
Weakening of the plant: By sucking the sap, the psyllas weaken the plants, causing deformations in the leaves, yellowing and loss of vigor.
Presence of honeydew and sooty mold: The honeydew produced by the nymphs favors the appearance of sooty mold, which reduces the photosynthetic capacity of the leaves by covering them with a black layer.
Attract other pests: The production of honeydew is the best attraction for the presence of other insects and pests that will affect the plants.
Disease transmission: Many species of psylla act as vectors of pathogens, transmitting viruses or bacteria to plants. For example, the potato psylla (Bactericera cockerelli) is a vector of the bacterium Candidatus Liberibacter, responsible for severe diseases in solanaceous crops. Or the Asian or citrus psylla, Diaphorina citri, which transmits the bacterial disease known as Huanglongbing (HLB), one of the most serious diseases of citrus in recent years.
### Most Significant Types of Psilas ###
Psylla pyri (pear psylla): This species is found mainly in pear trees, and is responsible for deformities in leaves and fruit, as well as loss of vigor. The nymphs produce abundant honeydew that causes the development of sooty mold, affecting the quality and quantity of the fruit.
Bactericera cockerelli (potato or tomato psylla): Common in solanaceous crops such as potato, tomato and pepper, this psylla is an important vector of the Candidatus Liberibacter bacteria. Infection by this bacteria causes serious problems in crops, such as “striped potato” or “zebra potato” syndrome.
Trioza apicalis (celery psylla): This species affects carrot and celery crops, especially in cold climates in Europe. It causes deformations and weakening of the plants, which significantly reduces the quality of the harvest.
Diaphorina citri (Asian citrus psyllid): This insect is a major vector of HLB (Huanglongbing or citrus greening disease), one of the most devastating diseases for citrus crops worldwide. It mainly affects trees such as orange, lemon and mandarin trees, causing yellowing of leaves, deformation of fruits and, eventually, death of the tree. Its presence is especially problematic in tropical and subtropical regions.
Euphyllura olivina (olive psylla): This insect affects olive crops, feeding on young shoots, flowers and fruit. Its activity causes deformation and premature fall of flowers and fruit, significantly reducing production. In addition, the honeydew it secretes encourages the development of fungi such as sooty mold, which affects the quality of olive oil. It is a common pest in Mediterranean regions.
Macrohomotoma gladiata (ficus psylla): This insect mainly attacks ornamental ficus species, feeding on tender shoots and young leaves. Its activity causes deformations, stunted growth and weakening of the plants. It also secretes honeydew, which encourages the appearance of fungi such as sooty mold, affecting the aesthetics and health of the trees. It is an emerging pest in urban areas and zones with warm climates.
Glycaspis brimblecombei (eucalyptus psylla): This insect is an invasive pest that affects several species of eucalyptus, feeding on the sap of the leaves. Its activity causes water stress, severe defoliation and, in extreme cases, the death of the tree. In addition, it produces a waxy structure called lerpa, which protects the insect and makes it difficult to control. It is a particularly problematic pest in warm regions where eucalyptus is widely cultivated for wood and paper.
### Protection Mechanisms of Psyllid Nymphs ###
Psyllid nymphs employ a variety of protective strategies to survive adverse environmental conditions and natural predators. These adaptations are especially important during their immature phase, when they are vulnerable. Some of the most prominent mechanisms are detailed below:
Production of Cottony Secretions or Protective Waxes
Some species of psylla, such as the olive psylla (Euphyllura olivina) and the ficus psylla (Macrohomotoma gladiata), produce a cottony secretion in the form of a white coating that covers the nymphs. This “cotton” coating is mainly composed of waxes and serves several functions:
Physical protection: Acts as a barrier against dehydration, helping nymphs retain moisture in dry conditions.
Defense against predators: This cottony covering confuses or hinders the access of natural enemies, such as predators or parasitoids.
Camouflage: Their cottony appearance allows the nymphs to blend better into the environment, making them less visible.
Formation of Protective Shields
Some psyllae develop a type of shield or shell over the body of the nymphs, which provides them with additional protection. This shield can be made of waxy substances or hardened secretions:
Waxy shield: In species such as Cacopsylla pyri (pear psylla), nymphs produce a waxy coating that helps them resist attack by natural enemies.
Protection against insecticides: These shields can make it difficult for chemicals to penetrate, making nymphs more resistant to certain treatments.
Cooperative protection
The symbiotic relationship between ants and psylla allows them to have “external protection” in the form of surveillance and defense by the ants, which keep predators away to protect their food source, the honeydew produced by the psyllas.
Behavioral resistance
Some psyllas have behaviors that help reduce their exposure to danger:
Immobility and grouping: In certain species, nymphs group together and remain motionless on the underside of leaves, which reduces their visibility and exposure.
Refuge in young shoots: By locating themselves in young shoots or hard-to-reach areas on plants, nymphs avoid detection and attack by larger predators.
### Psila Control Measures ###
Management of psylla requires an integrated approach that includes biological, cultural and monitoring methods:
Biological control: Natural predators such as lacewings, ladybirds, and certain parasitoids can help reduce psyllid populations. These species feed on eggs and nymphs, contributing to natural control that minimizes the use of chemicals.
Cultural control: It is recommended to remove infected crop residues to prevent psyllids from moving from one season to another. In addition, keeping the crop free of weeds reduces the refuge sites for the pest. Pruning practices in fruit trees also limit the access of psyllids to tender shoots, making their reproduction difficult.
Monitoring and Traps: Yellow sticky traps are useful for identifying the presence of psyllids in crops and allowing for an early response. Frequent monitoring is key to avoiding severe infestations and applying appropriate control measures in a timely manner.
### Chemical and Biological Treatments ###
The use of treatments must be part of an integrated and environmentally friendly strategy:
Insecticides: Psyllid-specific insecticides can be effective, but it is essential to rotate products with different modes of action to prevent the development of resistance. In addition, due to the production of scutes and waxes, insecticides must be systemic and active with ingestion. Some recommendations:
Acetamiprid
Deltamethrin
Esfenvalerate
Tau fluvalinate
Biological products: Alternatives such as azadirachtin (neem extract) and mineral oils offer less aggressive options with less environmental impact. These products can be applied in combination with other control measures to achieve an effective reduction of the pest. It should be noted that these treatments have an effect mainly on adults since the nymphs are protected by waxy shields.
Psyllids pose a significant threat to a variety of crops, and their management requires a comprehensive approach that combines preventative measures, monitoring, and targeted treatments. Implementation of biological and cultural control techniques, along with prudent use of insecticides and biological alternatives, can help keep psyllid populations under control and ensure crop productivity and health.
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