Maize Leaf Weevil – Tanymecus dilaticollis

Tanymecus Dilaticollis

Tanymecus Dilaticollis

Distribution:

This insect is spread in the European and Western Asian continent, in the maize farming areas. It has been reported as a pest in countries such as Iran, Russia, Greece, Bulgaria. In Europe, the maize lead weevil was reported in 1904; it is often found in steppe and forest steppe areas, on wide areas, on the plain areas of the continent,  and in the valleys of the main rivers. It  presents a major economic importance, especially in south, east and south-east.

Description

The adult is grey-brown colored, ventrally lighter colored, 6.5-8mm long. The adult is elongated oval shaped, characterized by the presence of a beak called rostrum, which is longer than the body.

Tanymecus Dilaticollis - adult

The egg is 0.5-1 mm long, cylindrical, rounded on the sides, yellowish-white, then turning darker and getting brown. The larva is apodous, reaching 8-9 mm at maturity, bright white colored with yellowish pilosity. The pupa is white colored, 5-9 mm long. 

Biology and ecology:

 It is a monovoltine species (one generation per year) and it overwinters as an adult in the soil, in the nymphic box, at a depth of 40-60cm. When the soil temperature is 4º C (February), the insects leave the overwintering place, moving towards the superficial stratum of the soil, where they wait for favorable conditions (temperatures 9º C), which are characteristic to the end of March – beginning of April, when they get to the surface of the soil.

From April until maize rise, adults feed with small-grain cereals or different spontaneous plants, especially bonitos. Once the maize rises, the pest focuses on this crop, where it feeds intensely, copulates and lays eggs.

The pest is particularly active during sunny and warm periods, when the soil temperature is over 18°C and which goes until June (about 80 days). The majority of the eggs are laid in the maize crop, isolated or in groups of up to 10 eggs, at a short depth in the soil or under the ground rocks. One female can lay up to 100 eggs. After extrusion (1-4 weeks since the eggs are laid), the larva feeds with maize roots, gradually going deeper into the soil, following the rooting system of the plant, up to a depth of 40-60 cm.

Affected plants and damage:

It is considered the most important maize pest, but it also feeds with other cultivated plants, causing severe damage (sunflower, sugar beet, sorghum, soy, Lucerne, corn, barley). When the plants are in an initial stage of 2-3 leaves, the adult cuts the plant from the collet, causing mass destruction of the crop, which requires crop reseeding. Also due to the attack at the base of the plant, the flag leaves later present circular punches, transversally disposed on the limbus.

Tanymecus Dilaticollis - damage

Plants attacked during emergence, up to the phase of 2-3 leaves, can be chafed in the collet area. The maize plants after the phase of 4-5 leaves no longer represent a food source for the pest, which moves to other spontaneous plants.

Tanymecus Dilaticollis - affected plant

The only plant in the spontaneous flora which meets the requirements of this species is the bonitos.

Prevention and control

The most effective and secure control method for this pest is the treatment of the seed, which can be done with the following insecticides: Seedoprid 600 FS (8 l/ton).

During vegetation stage, treatments with the insecticides Actara (0.1 kg/ ha), Calypso 480 SC (150 ml/ha), Mospilan 20 SG (100 g/ha) are recommended.

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