Tuta Absoluta

Tuta absoluta, a member of the Lepidoptera family Gelechiidae, poses a significant threat to tomato plants and fruits, and has been known to infest other plants belonging to the Solanaceae family. Additionally, it has been observed on Solanaceae family weeds such as Solanum nigrum and Datura spp. Recently, Tuta absoluta has emerged as a major concern for tomato production in Kenya.

Controlling Tuta absoluta is extremely challenging. The effectiveness of chemical control methods is limited due to the insect’s destructive behavior and its ability to rapidly develop resistance to insecticides.

Damage caused

The larvae of Tuta absoluta create extensive tunnels within tomato leaves, resulting in significant damage to both greenhouse and open-field tomato production. They also burrow into the fruit, leading to substantial losses. These larvae primarily feed on the mesophyll tissues, creating irregular mines on the leaf surface. One of the most recognizable symptoms is the presence of blotch-shaped mines on the leaves.

Within these mines, both the caterpillars and their dark frass (excrement) can be found. The mining activity causes deformation in the affected plants. Furthermore, the damage to the fruit creates opportunities for fungal diseases to enter, resulting in the rotting of the fruit either before or after harvest. The impact of Tuta absoluta can lead to a yield reduction of 50% to 100% in tomatoes, rendering severely attacked fruits unmarketable.

Eggs

The eggs of Tuta absoluta are small and cylindrical, measuring approximately 0.35 mm in length. They have a creamy white to yellow coloration. The hatching of these eggs occurs within a period of 4 to 6 days after they are laid.

Larvae

The larvae of Tuta absoluta exhibit a cream coloration with a distinct dark head. They undergo four instars during their development. Unlike some insects, Tuta absoluta larvae do not enter diapause when there is an ample food supply. As they progress through the second to fourth instars, the larvae transition to a greenish to light pink hue. The larval stage is the most destructive phase, lasting approximately 12 to 15 days.

Pupa

The pupae of Tuta absoluta display a brown coloration. Pupation can occur in various locations, including the soil, on the leaf surface, or within the mines created by the larvae. Importantly, this pupal stage does not result in any harm to the crop. The pupal phase typically lasts for a duration of 10 days, completing the development process.

Adult

The adult Tuta absoluta insects are active during the nighttime and seek shelter between leaves during daylight hours. They measure approximately 5-7 mm in length, with a wingspan ranging from 8-10 mm. Adult females lay their eggs on host plants, and a mature female can lay up to 260 eggs throughout her lifespan.

Tuta absoluta has the ability to go through about 10-12 generations in a single year. The entire life cycle, from egg to adult, is typically completed within a span of 30-35 days.

Management of Tuta absoluta

Chemical control

Since its emergence in the country, chemical control has been the primary method employed to combat Tuta absoluta. Several products have been officially registered for the purpose of controlling this pest. However, despite the availability of numerous pesticides approved for managing Tuta absoluta, their effectiveness is generally limited to low to moderate levels. This is primarily due to the larvae’s ability to conceal themselves and the insect’s high reproductive capacity. Moreover, there have been reports of insecticide resistance occurring in several cases.

Chemical Recommendation

The following chemical recommendations are provided for controlling Tuta absoluta:

Option 1:

  • ESCORT: Mix 10ml of ESCORT with 20 liters of water.
  • INTEGRA: Mix 3ml of INTEGRA with 20 liters of water.

Option 2:

  • ALONZE: Mix 3ml of ALONZE with 20 liters of water.
  • INTEGRA: Mix 3ml of INTEGRA with 20 liters of water.

These recommended chemical combinations can be used as an effective strategy for managing Tuta absoluta infestations.

Biological Control

In both open field and greenhouse tomato cultivation, various biocontrol agents are employed to combat the tomato leaf miner. Among these agents, mirid bugs are the predominant predators known to prey on Tuta absoluta. Additionally, Bacillus thuringiensis (BT)-based insecticide formulations have been utilized for controlling Tuta absoluta in areas where it is native as well as in regions where it has invaded.

While biological control methods offer certain advantages, such as being environmentally friendly, they do have limitations. One such limitation is their relatively slow action, making them less effective when populations of Tuta absoluta are high.

Cultural Control

Various strategies have been employed to control the pest, Tuta absoluta. These include ploughing, manuring, irrigation, crop rotation, solarisation, and the removal of symptomatic leaves, as well as the destruction of tomato plants that have been infested.

To effectively manage Tuta absoluta, it is highly recommended to eliminate alternative reservoir hosts, especially nightshades, both before and during the crop cycle. By removing these potential sources of infestation, the overall control efforts can be significantly enhanced.

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