Eurygaster genre sunn pests are spread across Europe, Asia and North Africa. 3 such species are reported to be wheat pests: Eurygaster maura, Eurygaster austriaca si Eurygaster integriceps.
In Europe, Eurygaster integriceps is the most propagated one. The other species do not form numerous populations. Biology, ecology, damage method and control are similar to all 3 species, and they only present some morphological differences. Furthermore, we will elaborate around the Eurygaster integriceps species, which is the most spread in Europe.
The damage area of this pest goes on the outside of the European continent. The species is spread across 22 counties, affecting over 1 million wheat hectares.
Adults have an oval aspect, with the body length of 11-13 mm. The color variety is wide, starting from brownish-yellow, to fully dark. The head is triangular and the foregoing extremity is three-cusped, which is important for the species identification. The antennae are long. The scutellum is well developed, sometimes longer than the abdomen apex, and covers the wings.
The egg is spherical, green colored when freshly laid and, as the egg develops, it gets darker.
The larvae, after hatching are almost spherical, and with the advancement through the 5 instars up to maturity, they resemble the adults more and more, but smaller and wingless.
Biology and ecology:
This pest develops one generation per year and overwinters as an adult under leaves, in the broad leaved forests. It gets active in spring, when the average daily temperature ranges from 10°C to 15°C. Mass migration, however, starts when the average temperature reaches 18-20°C, favored by warm weather and lack of fallout. After it migrates on spontaneous Gramineae and wheat, the sunn pests go through a feeding and sexual maturity period. Copulation and egg laying follow. Mass egg laying takes place at the end of May, beginning on June, on leaves, stems, but especially on the culm and on the newly formed wheat-ears. One female can lay 70-100 eggs, depending on its fat reserve. Egg incubation lasts and is followed by the 5 larval instars, up to the adult instar (30-40 days).
After the sunn-pests are established on the crops, their damaging characters can be noticed in Mai-July. The larvae which appear after the wheat-ear forms, feed with the freshly formed spikelets.
Adults feed intensely with spikelets, for 10-12 days, to store as much reserve substances as possible. The reserve substances are absolutely necessary for the development of the vita l processes during the diapause and breeding period. The intense feeding period overlaps the full ripening of the wheat, thus with the harvesting period.
After the storage of the required reserve substances, adults migrate to enter diapause under the leaves of the broad-leaved forests, up until the next spring. The migration moment to the hibernation places varies depending on the region and climate. Usually, the development cycle ends before wheat harvesting.
The sunn-pest is a thermo-sun-loving insect; the processes that take place starting from the diapause ending up to full development of the adults are favored by warm, dry weather, lack of winds and strong light. On the opposite side, cold, wet weather, with strong winds inhibits normal development, with severe consequences on the numerical force.
Affected plants and damage:
It is an oligophagous species, developing especially on wheat, but it also attacks other cultivated and spontaneous Gramineae. The attack is gradual, starting end of April until harvest, and during this time, all parts of the plant are attacked: the stem, leaves, wheat-ear and spikelet.
The attack is different depending on the generation. Adults feed with the vegetal organs, the attacked leaves turn yellow, they curl and wither at the pricking point. The attack on the stem, when the spikelet is in the culm, can lead to spikelet withering.
The larvae and young adults feed exclusively with the wheat-ears. At the pricking point, a small swelling forms which is called “salivary cone”, around which a yellowish area forms. Sometimes, the spikelet remains in the culm and when it emerges, it presents wavy bears and can be totally or partially sterile, whiteish. The attacked wheat-ears are wrinkled and carry the stamps of pricking under the form of black spots, surrounded by a discolored area. Pricking caused by sunn-pests lead to weight reduction, seed crop value drop, and especially to the depreciation of bakery products quality of the attacked crop. The enzymes secreted by the sunn-pests, which penetrate the wheat-ear during the feeding process, lead to gluten degradation and elasticity loss.
Adults’ attack takes place on the aerial parts of the plant, mainly on the leaves and stem, and leads to quantitative losses, and the larva and new generation attack takes place closer to the wheat-ears, leading to quality losses.
Control and prevention
Currently, chemical control is the only effective control method for crop protection against these pests.
For control action planning, annual pest appearing prognosis needs to be elaborated, which can be done by estimating the populations in a specific area. The density of the existing pests on the stalky cereals before harvesting is taken into account, as well as the attacked wheat-ears. In broad-leaved forests, controls must be performed in autumn and spring, to evaluate the reserve of adult pests.
Recommendations of crop treatments will be made, for the crops in rotation where the economic damage limit has been reached. The economic damage limit (EDL) for the hibernating generation is of 7 adults/m², for crops with an optimal density, properly fertilized and where the plant phenology corresponds to the months when the probing was made. For cultures without optimal density, non-fertilized and where the plant phenology does not correspond to the month when the probing was made, the ELD is of 5 adults/m².
For the new generation, the ELD is established depending on the count of I and II instar larvae, as described: 5 individuals/m² for crops with optimal density, well fertilized and where the plant phenology corresponds to the month when the probing was made and 3 individuals/m² for crops without optimal density, which were not properly fertilized. For crops for seed production, the ELD is 1 individual/m².
The sunn-pest has many natural pests and parasites, such as: wasps which are a parasite for the eggs (Telenomus chloropus, Trissolcus grandis), oophagous flies from the Phasinae family, invertebrates and vertebrates which feed with these pests.
Species with early maturity are recommended, to reduce the impact of the new adults on the crops, or earlier harvesting of the crops, in favorable weather conditions.
Considering the severe impact over the crop, the large area where it can be found and high densities in wheat crops, cereal crop protection against this pest is recommended.
Chemical prevention will be done at warning, taking into consideration the density of the pest, the crop vegetation stage and the weather conditions of that specific year.
Products recommended for sunn-pest control: Mospilan 20 SG, Biscaya 240 OD, Novadim Progress, Pyrinex Quick, Actara 25 WG, Kaiso Sorbie 5 WG, Mavrik 2 F, Karate Zeon 50 CS, Cylotrin 60 CS.