Phytophagous Insects and Plant Pests: Causes, Damage, and Integrated Pest Management

Phytophagous Insects

Phytophagous insects feed on crops and other plants, using them to meet their vital needs, such as feeding, reproduction, and shelter. When their damage results in significant economic losses, phytophagous organisms are considered a pest.

Phytopathogens

Phytopathogens are the agents that cause plant diseases. Saprophages are generally considered beneficial, as they contribute to the process of nutrient recycling, and some act as true antagonists of phytopathogens.

Weeds

Vascular plants known as weeds grow in the cultivated area, competing with crops for resources such as nutrients, light, space, and water, which affects their production. When weeds are not controlled, their harmful action on crops can be significant. Weeds are often found along roadsides and in ruderal areas.

Physiopathies

Physiopathies are disorders and abnormal plant physiology caused by ecological or abiotic factors that are not normally present in nature.

Disease

A disease is a process caused by the continuous action of a pathogenic agent, resulting in harmful effects on the living system and the symptoms that follow. The agents that cause diseases are called pathogens, and their study is the object of plant pathology.

Damage

Damage is a process caused by a single, sudden action, whether or not it is continued, and it is traumatic to the plant. The agents that cause damage are the object of study of phytophagous insects and agricultural entomology.

Chemical Control

Pesticides are particularly powerful agents of change. Their introduction into agriculture allowed the simplification of many exogenous variables that producers would otherwise need to manage.

Biotechnological Control

In 1966, the discovery of juvabione, a natural analogue of the juvenile hormone of insects, led to the development of the first new pesticides: insect growth regulators (IGRs). These compounds alter the growth and development of insects.

Biological Control

Biological control methods are highly effective against insect pests and similar organisms. They use natural enemies, such as parasitoids, predators, and pathogens, to attack and destroy these pests.

Intervention

The appropriate intervention depends on the moment and the technical product used.

Diagnosis

Diagnosis depends on the disease, the plant, and the environment.

The Disease

The disease depends on the virus, the plant, and the environment.

Preventing Diseases

Preventing diseases requires understanding the mechanism of infection and choosing the location carefully. Key measures include:

• Using resistant or tolerant varieties
• Maintaining clean fields with crop rotation
• Eliminating infected plants and pruning
• Keeping the soil well balanced and maintaining healthy plants through proper irrigation, pruning, and fertilization
• Avoiding excessive or insufficient fertilization
• Learning to tolerate certain diseases

Preventive fungicides are not curative. A correct diagnosis at the very beginning is essential.

Weeds as Hosts

Some weeds serve as hosts for agents that harm crops and can facilitate the spread of disease. They also regulate temperature and can host beneficial agents that support the crop.

Parasitoids

Parasitoids require a single host to complete their life cycle. They can be endoparasitoids, which develop inside the host, or ectoparasitoids, which act externally.

Hormesis

Sublethal doses of substances considered harmful can be beneficial when applied to organisms under suboptimal conditions.

Natural Control

Natural control is the biotic regulation of populations by biotic and abiotic agents within a given ecosystem. In this way, the population fluctuates in density over a given period, between upper and lower limits.

Biocontrol

Biocontrol reduces the density of a specific pest population through the action of its natural enemies.

Maximum Residue Limits

The maximum residue limit (MRL) is the highest legally acceptable concentration of a pesticide residue on or in a food, agricultural product, or animal feed.

Disease Conditions

Pathogenic conditions: Clean the field area and remove leaves and debris where infections can develop. Phytophagous vectors, predators, and viruses can enter through these areas. Prune carefully and maintain optical and physical hygiene.

Susceptible plants: Provide adequate water, avoiding both excess and deficiency. Fertilize appropriately, and prune with care. If an infected tree is detected, choose genetically resistant varieties.

Favorable environment: Apply treatments at the right time and by the appropriate method. Avoid conditions favorable to disease, such as excess humidity, which promotes fungal growth.

Mediterranean Fruit Fly (Ceratitis capitata)

Metamorphosis: The transition from larva to adult involves a change in form and in the definitive characteristics needed for reproduction. This change is accompanied by major morphological and physiological transformations, with important consequences for pest control. The shift from larva to adult also changes feeding needs, so identifying the optimal moment to attack the pest is essential. Because the change in feeding behavior does not occur in an incomplete metamorphosis, the approach and the amount of product to apply will vary.

Mites

• Phytoseiids: predators, beneficial to crops
• Tydeids: saprophages
• Eriophyids: phytophagous, such as the grape erineum mite
• Tetranychids: phytophagous, such as Panonychus citri

Scale Insects

• Lecanines: produce honeydew; nymphs are mobile; for example, the black scale
• Diaspidids: do not produce honeydew; first-instar nymphs (crawlers) are mobile; for example, the red scale
• Pseudococcids: produce honeydew; crawlers are mobile; for example, Pseudococcus spp. on grapevine
• Margarodids: produce honeydew and are mobile; for example, the grooved scale