Insects on plants? Guide to know what they are, damage and how to combat them
- Jesús Martínez
- Mar 27
- 16 min read
Phytophagous insects represent one of the main threats to plant health. Their feeding can weaken crops, transmit diseases, and significantly affect agricultural production. In this article, we'll explore the most common pests, their characteristics, the damage they cause, and strategies for their control.
1. Aphids (Aphididae)
Aphids are small, soft-bodied insects that feed on plant sap. There are many different species, and although they vary in color (green, black, yellow, brown, or even pink), they all share similar characteristics. They reproduce rapidly, allowing them to form large colonies in a short time. They are especially problematic in agricultural crops, orchards, and gardens, as they can weaken plants and transmit plant-pathogenic viruses.
Identification
Aphids measure between 1 and 4 mm in length, have a pear-shaped body, and are usually found in clusters on tender shoots, the undersides of leaves, and young stems. Some species develop wings when populations are large and need to disperse. They have two tubular structures on the back of their abdomen called cornicles, which secrete defensive chemicals.
Signs/damage
Aphids pierce plant tissue with their sucking mouthparts and extract sap, weakening the plant and causing:
Curled, yellowed, or deformed leaves.
Stunted growth.
Presence of honeydew, a sticky substance they excrete that promotes the growth of fungi such as sooty mold (black sooty mold).
Attracts ants, which protect aphids in exchange for feeding on their honeydew.
Transmission of plant viruses, which can cause serious diseases in crops..
Control
To control aphid populations, several methods can be applied:
Biological control: Introduce natural enemies such as ladybugs (Coccinellidae), lacewings (Chrysopidae), or parasitic wasps (Aphidiinae).
Cultural methods: Prune infested parts, avoid excess nitrogen in fertilizers, promote biodiversity in the garden, and use colored or sticky traps.
Homemade solutions: Spray with soapy water, garlic extract, or neem oil.
Chemical control: In severe cases, specific insecticides can be used, but always with caution to avoid harming beneficial insects. Formulations based on acetamiprid, azadirachtin, cypermethrin, deltamethrin, esfenvalerate, or pyrethrins.
Want to know more about aphids and how to get rid of them?
Do you want to know how to make your own homemade adhesive traps?
2. Mites (Tetranychidae, Eriophyidae and Tarsonemidae)
Spider mites are tiny arthropods that affect a wide variety of plants, from agricultural crops to ornamentals. They are close relatives of spiders, and like them, some species produce fine webs on their leaves. Although they are difficult to detect with the naked eye due to their microscopic size, their rapid reproduction and suction-based feeding can seriously weaken plants.
Identification
Mites vary in color depending on the species and stage of development, and can be red, yellow, green, brown, or translucent. They measure less than 1 mm in length and are usually found on the undersides of leaves. The most common species include:
Spider mites (Tetranychidae): Produce fine webs and leave a stippled appearance on leaves.
Eriophyid mites (Eriophyidae): Are microscopic and cause deformations in leaves, stems, and fruit.
Tarsonemidae mites (Tarsonemidae): Attack young shoots and deform plant growth.
Signs/damage
Symptoms of mite infestation include:
Leaves with yellow or bronze speckles.
Fine webbing on the undersides of leaves and between stems.
Deformed, dry, or drooping leaves.
Plant growth retardation.
Mites thrive in warm, dry environments, so prolonged periods of heat promote their proliferation.
Control
To manage mite populations, several strategies can be applied:
Biological control: Introduce natural predators such as the Phytoseiulus persimilis mite or the green lacewing (Chrysopidae).
Cultural methods: Maintain adequate humidity, avoid water stress, spray with water to hinder their development, and use colored or sticky traps.
Homemade solutions: Apply garlic extract, neem oil, or potassium soap.
Chemical control: Use horticultural oils and acaricidal products based on abamectin, hexythiazox, lambda cyhalothrin, or tau-fluvanilate.
Do you want to know more about mites and how to eliminate them?
3. Whiteflies (Aleyrodidae)
Whiteflies are small, sucking insects that feed on plant sap. Despite their name, they are not true flies, but close relatives of aphids and mealybugs. They are usually found in large groups on the undersides of leaves and are common pests in agricultural crops, gardens, and greenhouses. In addition to weakening plants, they can transmit plant viruses and facilitate the growth of fungi.
Identification
Adult whiteflies measure between 1 and 3 mm in length and have white wings covered with a waxy substance. Their larvae are small, yellowish, and remain attached to the leaves while they complete their development. Whiteflies usually congregate on the undersides of leaves, and when the plant is shaken, the adults quickly fly away in small swarms.
Signs/damage
The main symptoms of a whitefly infestation include:
Yellowed and weakened leaves due to sap extraction.
Presence of sticky honeydew, which promotes the growth of fungi such as sooty mold (black sooty mold).
Premature leaf drop.
Transmission of plant pathogenic viruses, which can seriously affect crops such as tomatoes, peppers, and cabbages.
Control
To combat whitefly, various strategies can be applied:
Biological control: Introduce natural predators such as ladybugs, parasitic wasps, and lacewings, or use fungi such as Beauveria bassiana.
Cultural methods: Place yellow sticky traps, maintain crop rotation, avoid excessive nitrogen fertilization, and use highly effective colored or sticky traps (yellow).
Homemade solutions: Apply potassium soap, neem oil, or garlic and chili extracts.
Chemical control: In severe infestations, use specific insecticides such as pyrethroids or those based on acetamiprid, azadirachtin, cypermethrin, deltamethrin, lambda-cyhalothrin, or esfenvalerate.
Do you want to know more about whiteflies and how to eliminate them?
4. Leaf miners (Agromyzidae and Gracillariidae)
Leaf miners are insect larvae that feed on the inner tissue of leaves, creating visible tunnels in the form of irregular lines or spots. These tunnels affect the plant's photosynthetic capacity and can significantly weaken it if the infestation is severe. Various insect species can cause this damage, including fly larvae (Agromyzidae), moths (Gracillariidae), and beetles.
Identification
Adults vary by species:
Leaf miner flies (Agromyzidae): Small, black or gray, with transparent legs and wings.
Leaf miner moths (Gracillariidae): Tiny butterflies with narrow wings and fine hairs on their bodies.
Leaf miner beetles: Small, usually dark, with larvae that bore into leaves and stems.
The larvae are white or pale yellow and live within the leaf tissue, forming meandering galleries or irregular patches.
Signs/damage
Translucent galleries or tunnels on the leaf surface.
Deformed, yellowing, or dry leaves.
Reduced plant growth due to reduced photosynthesis.
Black dots in the galleries, which are larval excrement.
Leaf miner species affect horticultural crops such as tomatoes, spinach, citrus fruits, and ornamentals, weakening the plants and making them more susceptible to disease.
Control
Biological control: Introduce parasitic wasps, which attack the larvae, and use biocontrol agents such as Bacillus thurigiensis.
Cultural methods: Remove and destroy infested leaves, avoid monoculture, and rotate crops.
Homemade solutions: Apply neem oil or potassium soap to reduce the presence of adults.
Chemical control: In severe cases, use systemic insecticides such as acetamiprid, azadirachtin, deltamethrin, lambda cyhalothrin, or spinetoram.
5. Leafhoppers (Cicadellidae)
Leafhoppers, also known as leafhoppers, are small insects that feed on plant sap using their piercing-sucking mouthparts. They are extremely mobile and can jump or fly rapidly when threatened. In addition to weakening plants, many leafhopper species are vectors of plant pathogenic diseases, such as phytoplasmas and viruses, making them a dangerous pest of agricultural and ornamental crops.
Identification
Adult leafhoppers typically measure between 2 and 15 mm in length and have elongated bodies with variable colors, from green and yellow to brown or striking patterns. Their wings are membranous, and their most notable feature is their jumping ability, thanks to their well-developed hind legs. Nymphs are similar to adults but lack fully developed wings.
Signs/damage
Stippling or discoloration of leaves due to sap leaching.
Stunting or stunted growth in affected plants.
Presence of sugary excrement on leaves, which can attract fungi such as sooty mold.
Transmission of plant diseases, such as "rice thread leaf" or "citrus variegated chlorosis."
Control
Biological control: Encourage the presence of natural predators such as ladybugs, lacewings, and parasitoid wasps, and apply parasitoid nematodes such as Steinernema carpocapsae.
Cultural methods: Maintain crop rotation, eliminate host weeds, and avoid excessive nitrogen fertilization.
Homemade solutions: Apply garlic extract, potassium soap, or neem oil to the leaves.
Chemical control: In severe infections, use systemic or contact insecticides such as pyrethroids or those formulated with acetamiprid, azadirachtin, cypermethrin, deltamethrin, lambda-cyhalothrin, or esfenvalerate.
6. Thrips (Thysanoptera)
Thrips are small, elongated insects that feed by piercing plant cells and sucking out their contents, causing damage to leaves, flowers, and fruits. They are common pests in greenhouses, agricultural crops, and ornamental plants. Furthermore, some thrips species are vectors of plant pathogenic viruses, such as Tomato spotted wilt virus (TSWV), making them even more problematic for agriculture.
Identification
Adults: They measure between 1 and 2 mm long, with slender, elongated bodies, ranging in color from pale yellow to dark brown or black. They have narrow, fringed wings.
Nymphs: Similar to adults but wingless and lighter in color.
Signs/damage
Silvery or bronze spots on leaves due to cell destruction.
Deformities in leaves, flowers, and fruit.
Presence of excrement in the form of small black dots.
Virus transmission in crops such as tomatoes, peppers, and lettuce.
Control
Biological control: Introduce natural enemies such as predatory mites (Amblyseius swirskii), lacewings, predatory bugs such as Orius spp., or predatory nematodes such as Heterorhabditis bacteriophora.
Cultural methods: Eliminate weeds, use blue or yellow sticky traps, and avoid excess nitrogen in fertilization.
Homemade solutions: Apply garlic extract, neem oil, or potassium soap to affected plants.
Chemical control: In severe cases, use selective insecticides such as spinosad, acetamiprid, azadirachtin, cypermethrin, deltamethrin, lambda-cyhalothrin, esfenvalerate, or pyrethroids.
Want to know more about thrips and how to get rid of them?
7. Caterpillars (Lepidoptera - Larvae of Butterflies and Moths)
Caterpillars are the larval stage of butterflies and moths. They are one of the most destructive agricultural pests, feeding on leaves, stems, flowers, and fruits, causing severe damage to horticultural, fruit, and ornamental crops. Depending on the species, they can consume large amounts of plant tissue in a short period of time and affect crop production.
Identification
Larvae: Soft, cylindrical bodies with three pairs of true legs on the thorax and up to five pairs of false legs on the abdomen. They typically measure from a few millimeters to 5 cm long, with varying colors and patterns depending on the species.
Adults: These develop into butterflies or moths of varying sizes and colors.
Signs/damage
Perforated or completely devoured leaves.
Presence of dark excrement on the leaves.
Silk cocoons on the plant (in species that form shelters).
Damaged fruits with perforations or internal galleries.
Severe defoliation in crops such as tomatoes, cabbage, lettuce, citrus fruits, and cereals.
Control
Biological control: Use of parasitoids such as Trichogramma spp., natural predators such as lacewings and ladybugs, or fungi such as Beauveria bassiana.
Cultural methods: Manually remove caterpillars and eggs, promote biodiversity to attract natural enemies, and rotate crops.
Homemade solutions: Apply neem extract, garlic infusion, or Bacillus thuringiensis (Bt), a natural bacteria that specifically attacks larvae.
Chemical control: Use selective insecticides in severe cases, preferably biological ones such as spinosad or lambda cyhalothrin to avoid harming beneficial insects. If you opt for chemical treatments, use formulations based on acetamiprid, cypermethrin, deltamethrin, esfenvalerate, or fosthiazate.
8. Mealybugs and scale insects (Coccoidea)
Mealybugs and scale insects are sucking insects that feed on plant sap using their specialized mouthparts. These pests are found on a wide variety of crops and ornamental plants, weakening them by extracting nutrients and leaving sugary secretions that encourage the growth of fungi such as sooty mold. Some species can also transmit diseases to plants.
Identification
Mealybugs: Covered in a white, cottony substance. They congregate on leaves, stems, and roots.
Scale bugs: They have a hard, rounded shell that adheres to branches and leaves, making them difficult to remove.
Nymphs: Small and mobile at first, but scale bugs become fixed as they mature.
Signs/damage
Loss of plant vigor due to sap suction.
Yellowing and deformation of leaves.
Presence of sticky secretions (honeydew or honeydew) that promote the growth of sooty mold.
Shells attached to stems and leaves in the case of scale insects.
Control
Biological control: Use natural predators such as ladybugs (Cryptolaemus montrouzieri) and parasitic wasps.
Cultural methods: Prune infested branches, improve plant ventilation, and remove plant debris.
Homemade solutions: Apply potassium soap, neem oil, or isopropyl alcohol directly to the mealybugs with a cotton ball.
Chemical control: In severe infestations, apply systemic insecticides such as abamectin, pyrethrins, acetamiprid, azadirachtin, cypermethrin, deltamethrin, lambda-cyhalothrin, pyriproxyfen, spirotetramat, tau-fluvalinate, or horticultural oils to suffocate the insects. It should be remembered that the scales are protected against contact insecticides or oils, which only affect the nymphs. Therefore, systemic insecticides must be applied to eliminate the adults.
Want to know more about mealybugs and how to get rid of them?
9. Beetles (Coleoptera)
Beetles are one of the largest and most diverse groups of insects, with thousands of species affecting plants. These insects can be both herbivorous and carnivorous, and in their larval and adult stages, some species cause significant damage to agricultural crops and ornamental plants. Beetles feed on leaves, stems, roots, or fruit, and many are also known for their ability to destroy crops in large numbers, such as the Diabrotica virgifera pathogen beetle or the Acanthoscelides obtectus beetle in beans.
Identification
Adults: Beetles have hard, oval or rounded bodies with well-developed antennae. Size varies by species, but generally measures between 3 and 20 mm long.
Larvae: They are typically curved, with segmented bodies, and are mostly white or cream-colored. They develop underground or in plant stems and roots.
Eggs: They are laid near roots or in tender shoots, depending on the species.
Signs/damage
Holes in or bitten leaves, affecting the plant's photosynthesis.
Damaged roots in the case of subterranean beetles, which can severely weaken plants.
Deformed fruit or signs of perforation in fruit and stems.
Presence of droppings or eggshells near affected areas.
Decreased quality and yield of crops such as corn, soybeans, and vegetables.
Control
Biological control: Introduce natural predators such as entomopathogenic nematodes like Steinernema sp., parasitoid wasps, and insectivorous birds.
Cultural methods: Crop rotation, removal of plant debris, and the use of trap crops to reduce beetle populations.
Homemade solutions: Use neem oil or insecticidal soaps applied to affected areas to deter or eliminate beetles.
Chemical control: In severe cases, insecticides such as pyrethroids or formulations based on acetamiprid, azadirachtin, cypermethrin, chlorantraniliprole, deltamethrin, lambda-cyhalothrin, or spinosad can be applied.
10. Fungus gnats (Sciaridae and Cecidomyiidae)
Fungus gnats are small insects belonging to the families Sciaridae and Cecidomyiidae. They are often referred to as fungus gnats because of their affinity for moist, humid environments with high organic matter, such as greenhouses and the soils of potted plants. Although adults do not pose a direct threat to plants, their larvae can cause severe damage to plant roots and growth systems.
Identification
Adults: Fungus gnats are small insects, approximately 2 to 5 mm long. They have a slender, black or gray body and translucent wings. Their long legs and antennae allow them to move easily in the air and on the soil surface.
Larvae: Larvae are translucent, with a black head and are worm-like. They can measure up to 1 cm long when fully grown. They are usually found in the topsoil or potting mixes, where they feed on plant roots and decaying organic matter.
Signs/damage
Presence of adult midges around recently watered plants or in areas with high humidity, such as greenhouses and indoors.
Root damage: Larvae feed on fine roots and decaying organic matter, which can weaken plants and cause them to wilt. Symptoms include yellowing leaves, stunted growth, and a damaged or rotten-looking root.
Root rot: Damage caused by larvae promotes root rot, which can lead to plant death if the infestation is severe.
Control
Biological control: Introduce natural predators such as entomopathogenic nematodes like Steinernema sp., bacteria like Bacillus thurigiensis, or certain predatory insects that attack fungus gnat larvae.
Cultural methods: Maintain a dry and well-ventilated environment to reduce excessive humidity, which favors the reproduction of these insects. It is also important to avoid overwatering, as humid conditions favor the proliferation of fungus gnats. Use colored or yellow sticky traps.
Chemical control: In cases of severe infestations, specific insecticides can be used against fungus gnats. Apply the insecticide locally, preferably to the area of the soil where the larvae feed.
Preventive techniques: Using a layer of coarse sand on the soil in pots or in the garden soil can help prevent the flies from laying eggs. Additionally, using yellow sticky traps can help reduce the adult mosquito population.
Controlling fungus gnats depends on monitoring humidity and implementing preventative strategies to prevent them from becoming a significant pest, especially in enclosed spaces such as greenhouses or houseplants.
11. Psyllids or Psilas (Psylloidea)
Psyllids, also known as psyllids or plant lice, are small, sap-sucking insects that feed on the sap of various plant species. They are especially problematic in fruit and citrus trees, where they can cause direct and indirect damage by transmitting diseases. Some species, such as Diaphorina citri, are vectors of citrus greening disease (Huanglongbing, HLB), one of the most devastating diseases for these crops.
Identification
Adults: Measure between 2 and 5 mm long, with elongated bodies and translucent wings. They may resemble miniature cicadas.
Nymphs: Flattened, with oval bodies covered in a white, waxy substance.
Eggs: They lay their eggs on tender shoots and the undersides of leaves.
Signs/damage
Curled or deformed leaves due to nymph feeding.
Waxy or sticky white excretions on shoots and leaves.
Honeydew and sooty mold as a result of the sugary secretion they produce.
Yellowing and weakening of the plant.
Transmission of diseases such as HLB in citrus, which causes fruit deformation and loss.
Control
Biological control: Introduce natural enemies such as parasitoid wasps, as well as predators like ladybugs and lacewings.
Cultural methods: Prune affected parts, remove excess tender shoots, and maintain a healthy garden.
Homemade solutions: Apply potassium soap, neem extract, or yellow sticky traps to capture adults.
Chemical control: In severe infestations, apply systemic insecticides such as abamectin, pyrethrins, acetamiprid, azadirachtin, cypermethrin, deltamethrin, lambda-cyhalothrin, pyriproxyfen, spirotetramat, tau-fluvalinate, or horticultural oils to suffocate the insects. It should be remembered that the nymphs of some species are protected under a shell, so contact insecticides or oils have little or no activity. Therefore, systemic insecticides must be applied to eliminate nymphs and horticultural oils to eliminate adults.
Want to know more about psyllids and how to get rid of them?
12. Phytophagous bugs (Hemiptera: Miridae, Pentatomidae, Coreidae, and others)
Plant-sucking bugs are sap-feeding insects that feed on plant sap and are among the main pests of agricultural and ornamental crops. These bugs are known for causing both direct damage, by piercing plant cells to extract sap, and indirect damage, by transmitting viral diseases. The most common species include green stink bugs (such as Nezara viridula) and plant bugs, which primarily affect tomato, cucumber, and pepper crops, among others.
Identification
Adults: Plant-eating bugs have bodies of various shapes (triangular, oval, or elongated), generally small to medium in size (5–15 mm long). Their color varies depending on the species, from green to brown to gray, and they usually have long antennae and legs adapted for jumping.
Nymphs: They are smaller than adults and generally lighter in color, with less defined body patterns.
Eggs: They are oval or elliptical in shape and are deposited on leaves or stems, usually in clusters.
Signs/damage
Leaf deformation: Plant-eating bugs cause yellow or pale spots due to sap sucking.
Fruit and seed deformation: In crops such as tomatoes and cucumbers, they can cause scarring or visible deformations due to feeding.
Necrosis or wilted areas may appear around the feeding area.
Sticky exudates (honeydew) on leaves and stems due to bug secretions, which also encourage the growth of fungi such as sooty mold.
Decreased crop yield by affecting photosynthesis and fruit formation.
Control
Biological control: Introduce natural predators such as ladybugs, which feed on eggs and nymphs, and parasitoid wasps that attack stink bugs in their immature stages, or use parasitic nematodes such as Steinernema sp.
Cultural methods: Eliminate infected plants or plant debris where stink bugs may inhabit. Rotate crops and use physical barriers such as netting to prevent stink bugs from entering crops.
Homemade solutions: Apply garlic extracts, potassium soap, or neem oil to repel or eliminate stink bugs.
Chemical control: In severe cases, insecticides such as pyrethroids or formulations based on acetamiprid, azadirachtin, cypermethrin, chlorantraniliprole, deltamethrin, lambda-cyhalothrin, or spinosad can be applied.
13. Weevils (Curculionidae)
Weevils are a family of insects within the order Coleoptera, known for their distinctive elongated snouts. They are common pests of a variety of agricultural crops and stored foods and can be found feeding on grains, seeds, roots, and other plant tissues. Many weevils are harmful both as adults and as larvae, when they feed on plants and store their eggs within plant tissues, causing significant damage.
Identification
Adults: Weevils are small to medium-sized insects, usually 2 to 10 mm long, with an elongated, oval body. They have a distinctive snout that allows them to pierce plants to feed and lay their eggs. Their color varies from brown to black to gray, depending on the species.
Larvae: They are small, white, and legless, with a curved body. They develop inside the plants or grains they infest, where they feed and cause damage.
Eggs: Adult weevils lay their eggs on plant parts being attacked, such as fruits, seeds, or roots.
Signs/damage
Holes in seeds, fruits, or roots due to larval feeding or adult pecking.
Empty or damaged grains (in the case of grain weevils), which can reduce the quality and quantity of stored crops.
Plant deformation due to larvae feeding on internal plant tissues.
Yellowing or wilting leaves, especially when weevils attack roots or stems.
Evidence of dust or rubbing debris in areas where larvae are feeding and burrowing.
Control
Biological control: Use natural enemies such as parasitoid wasps and predators like ladybugs or certain species of entomopathogenic nematodes, which attack weevil larvae.
Cultural methods: Remove infested plants, destroy plant debris after harvest, and rotate crops to prevent weevils from finding breeding grounds.
Homemade solutions: Apply neem oil, garlic extract, or potassium soap to repel or eliminate weevils from plants.
Chemical control: In severe infestations, weevil-specific insecticides such as pyrethroids can be applied locally to protect plants and minimize the impact on beneficial insects, or formulations based on cypermethrin, deltamethrin, lambda-cyhalothrin, tefluthrin, or chlorantraniliprole.
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