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Overview of the world's major lettuce pests and damage symptoms ​

Overview ​

Lettuce (Lactuca sativa) is an important vegetable crop around the world, but it is susceptible to damage from a variety of pests, leading to reduced productivity, quality, and loss of commercial value. Here, lettuce pests that are recognized as major and important worldwide, regardless of cultivation location or system, are comprehensively explained, including their biological characteristics, damage symptoms, and identification points. Includes information on the importance, geographic distribution, and management strategies for each pest, as well as references to the latest scientific and official sources.

Aphids (Nasonovia ribisnigri, Myzus persicae, Uroleucon sonchi, Acyrthosiphon lactucae) ​

Biology and Distribution ​

  • It is recognized as a very important pest in the world's major lettuce producing regions (e.g. the United States, Europe, Asia).
  • Typical examples include Nasonovia ribisnigri, Myzus persicae, Uroleucon sonchi, and Acyrthosiphon lactucae.
  • It multiplies rapidly under warm conditions, and occurs in open fields, greenhouses, hydroponics, and aquaponics.

Damage Symptoms ​

  • Forms colonies in young leaves and bulbs and sucks sap → yellowing, curving, and malformation of leaves.
  • “Sooty bacterium” develops in the affected area (caused by honey-like excrement = honeydew).
  • The damaged lettuce looks rough and its market value decreases significantly. There are many cases where products cannot be distributed due to contamination with unpleasant pests.
  • Highly capable of transmitting viruses and is the source of lettuce mosaic virus, potato leaf roll virus, etc.

Identification Features ​

  • Both adults and larvae are small insects with a body length of 1-2 mm. The body color is green, yellow or light brown, and Nasonobia species are found deep inside the bulb.
  • It is easy to overlook because it occurs in clusters in the center of leaves and bulbs, and in hidden areas.

Management notes ​

  • IPM, such as the use of predatory organisms (flying fly, lacewing, etc.) and lettuce resistant varieties, has become widespread.
  • Chemical pesticides are also causing drug resistance problems, and there are also regulations on the use of neonicotinoids (e.g., revised in California in 2024).
  • The most important group of lettuce pests worldwide [1][2][3][4][5][6][7].

Leminata (Liriomyza spp., especially Liriomyza huidobrensis) ​

Biology and Distribution ​

  • Liriomyza leafminers occur almost all over the world. L. huidobrensis has become a major problem in many places in recent years (even in Australia, it has been designated as an invasive and emergency pest).
  • Adults lay eggs within the leaf tissue, and the hatched larvae feed on the mesophyll in a meandering pattern.

Damage symptoms ​

  • Many white to light brown meandering tunnels (mines) appear on the leaf surface.
  • In severe cases, photosynthetic ability decreases, yellowing, withering, and loss of commercial value occur.
  • Damage is easy to overlook, and both yield and quality are greatly reduced.

Identification feature ​

  • The larva is a small white to translucent maggot type, and the adult is a small black and yellow fly about 2 mm in size.
  • Long, thin white linear tunnels meandering over the damaged leaves.

Management Notes ​

  • Cultivation control such as crushing compost residue around the field and "small fallow" is important.
  • Various insecticides (cyromazin, abamectin, spintram, etc.) are registered.
  • One of the world's most important pests [2][3][4][5][6][7][8].

Thrips (Frankliniella schultzei, F. occidentalis, etc.) ​

Biology and Distribution ​

  • An elongated insect (family Thripidae) with a body length of 1-2 mm.
  • Frequently occurring in tropical to temperate regions, both outdoors and in facilities. The problem is growing due to global warming and the increase in greenhouse cultivation in recent years.
  • F. occidentalis (western flower thrips) and F. schultzei (tobacco thrips) have a worldwide distribution.

Damage Symptoms ​

  • Scarred damage to leaves, buds, and flowers (silver-white to copper-colored spots, wrinkles, and atrophy).
  • Small black feces spots (excrement) on the damage site.
  • In severe cases, leaf blades become severely deformed and die.
  • Viral vectors such as tomato yellowing virus (mainly transmitted during the larval stage).

Identification feature ​

  • Small and slender adults and larvae near the damaged area, such as on the underside of leaves and inside new shoots.
  • The affected area is characterized by silvery-white scars and black spots.

Management notes ​

  • Rapid increase in high temperature and dry conditions.
  • Avoid resistance by using predatory mites, natural enemy insects, fungicides/insecticides (spintram, spinosad), and drug rotation.
  • Damage is particularly noticeable in cultivated facilities, warm areas, and dry areas [2][3][4][5][6][9][10]. ​

    Biology and Distribution ​

    • S. exigua and T. ni have caused significant damage in many parts of the world.
    • The larvae damage the young leaves of the plant, the growth points, and in some cases the interior of the bulb and the ground.
    • Multi-generational, occurs frequently in warm regions and warm seasons.

    Damage Symptoms ​

    • Pittling of leaves by larvae, chipping of leaves and stems (sometimes loss of commercial value due to core eating or head boring).
    • Brown spots and rot caused by larvae inside the bulb.
    • Due to damage to the entire leaf or the surface of the ground, growth is inhibited, withers, and yields are significantly reduced.

    Identification feature ​

    • Spodoptera larvae: Light-colored stripes on a green background, young develop from residual hairy egg masses in groups.
    • Cabbage diamondback moth larva: Green body color, unique locomotion style that moves in a loop.
    • Characteristic edges and perforations appear on the leaves.

    Management notes ​

    • Effective against natural enemies such as parasitic wasps, parasitic flies, and viruses.
    • Biological control agents such as bacterial preparations (Bacillus thuringiensis) and spinosad have also been put into practical use.
    • The use of resistant varieties (e.g. 'Valmaine', etc.) is also progressing.
    • A pest that is universally serious in hot seasons and production areas [4][5][6][7][11][12][13].

    Whiteflies (Bemisia tabaci, Trialeurodes vaporariorum) ​

    Biology and Distribution ​

    • Outbreak in more than 70 countries around the world, causing problems in almost all cultivated vegetables.
    • Bemisia tabaci (tobacco whitefly) has the highest number of damages and vectors.

    Vamage Symptom ​

    • Both adults and larvae suck sap from the underside of leaves, causing yellowing, curling, and impaired growth of leaves.
    • Soot disease caused by honeydew → Product value significantly reduced.
    • Diverse virus transmission such as begomovirus and lettuce yellowing virus.
    • Damage is likely to occur from the early stage of transplanting to the harvesting period.

    Identification feature ​

    • A white insect about 1-2 mm long on the underside of the leaf.The larvae are scale-shaped and easy to observe.
    • Yellowing and inversion around the suction site, excrement on the underside of the leaf.

    Management notes ​

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