Phyllotreta cruciferae
| Phyllotreta cruciferae | ||||||||||||
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Phyllotreta cruciferae |
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| Scientific name | ||||||||||||
| Phyllotreta cruciferae | ||||||||||||
| ( Goeze , 1777) |
Phyllotreta cruciferae , German glossy green coal flea , belongs to the flea beetles (tribe Alticini, subfamily Galerucinae) from the family of leaf beetles (Chrysomelidae).
features
Phyllotreta cruciferae becomes 1.8 to 2.5 millimeters in size. It has a metallic bluish, green or bronze color; the second and third antennae are yellow. Its elytra are strongly dotted. The spaces between the points on the pronotum are usually clearly wrinkled. Like all other Phyllotreta species, it is characterized by the thickened hind legs, which enable them to jump.
The eggs of the fleas are pale yellow, oval and have a length of 0.38 to 0.46 millimeters and a width of 0.18 to 0.25 millimeters. The larvae measure approximately three to five millimeters and are whitish, slender, cylindrical worms with small breast bones and a brown head capsule. The pupae are whitish, about the size of the adult beetles, and have black eyes.
Way of life
Earth fleas form one generation per year. As adult beetles, they usually hibernate from October to March in hedges, woods and the litter layer . They are also rarely found in canola stubble (stubble of 00 rape ). With the rise in temperature to 14 ° C, the beetles appear in spring. From a temperature of 17.8 ° C they can fly without restrictions. At the beginning of the growing season they feed on the leaves of the remaining vegetation, such as volunteer rape, wild mustard , weeds or overwintering host plants. With the progressive increase in vegetation, they continue to spread and feed in particular on the above-ground parts of the cruciferous plants . They prefer cruciferous vegetables that have recently sprouted. They are particularly active in warm, dry and windless weather with temperatures of 15 to 27 ° C. They mate around the end of May, after which the females lay up to 25 eggs in groups of one to four in the ground in June. The overwintered beetles remain active until around the end of June and begin to die off in early July. The larvae hatch from the eggs after about 12 days and feed on the secondary roots of the host plants. After the larval phase, which lasts 25 to 34 days, during which they go through three larval stages, pupae rest . This takes place in the ground and lasts about seven to nine days from early to mid-July. The beetles of the new generation hatch at the end of July to the beginning of September and also feed on the above-ground parts of the plant such as the leaves and pods of the Brassicaceae. In autumn they look for a shelter to hibernate.
Occurrence
They occur all over Europe and also in North America, where they were introduced as neozoa from Europe.
damage
The cabbage fleas cause damage to plants of different orders and families. The adult beetles damage mainly young plants from spring to autumn. They feed on the leaves of the host plants such as rocket , radish or radish and cause many small holes that look like a leaf perforated by shotgun. This damage is also known as pitting. In other Brassicaceae they cause what is known as window corrosion , in which only the outermost cell layer of the leaves is eaten. The leaf damage varies depending on the host plant. The greatest damage occurs within the first two weeks after germination. If the beetles are very competitive for feeding, even the growth point (the meristem or tissue ) of the plant is attacked, whereupon the plant dies. This damage can result in a severe harvest decline (fewer and smaller plants). The damage done to the roots by the larvae, on the other hand, is hardly worth mentioning, as their damage potential is less than 5% loss of yield. Damage is only done to radish and radish roots. Damage can also result from the transmission of diseases and viruses, because the fleas can transmit Alternaria brassicae , the pathogen that causes black cabbage. The viruses of the kohlrabi and radish mosaic virus can lead to yellow discoloration of the leaves along the leaf veins and also to growth disorders in young plants. In plants with a long vegetation period, such as rapeseed , the new generation of fleas at the beginning of autumn hardly cause any damage to leaves and pods, as the plants are already large enough. However, the upper, younger pods can be eaten away, as a result of which they contain fewer grains, dry out too early, shrink, crack or, in damp weather, be attacked by fungal diseases. In the case of plants with a short vegetation period, such as radishes, however, great damage can occur at this point in time due to a loss of yield or weight of the plants.
The economic threshold, which requires the use of foliar spray, is only reached when the cotyledons and the first real leaves are damaged by more than 25%, as well as the presence of cabbage fleas. With less than 20-25% leaf damage and good growth, the plant can usually recover. From the 4-leaf stage onwards, the canola plants endure more severe damage, which in years when there are plenty of beetles in June can result in a loss of yield of up to 10%, despite treatment with insecticides. The damage caused by eating fleas can be confused with that of springtails , which also feed on young Brassicaceae.
Host plants
Phyllotreta cruciferae attacks many cultivated plants as well as dicotyledon weeds. In contrast, it does not attack monocot plants and weeds such as grasses. Host plants are found in many plant families. The most popular are the Brassicaceae , in which it is the most common and most destructive pest, followed by the Capparaceae . Both families belong to the Brassicales order .
Combat
Planting date
Through early sowing and the resulting early development of the plants, during the phase in which the fleas are not yet very active, the yields of the plant stocks can be positively influenced. The early sowing reduces the heat and drought stress of the plants due to feeding spots and the feeding of fleas begins in a development phase of the plants in which they can tolerate it better.
Cultivation system
A firm, flat seedbed reduces the risk of feeding damage. An increase in the seed density reduces the damage to the individual plants, since the feeding activity of the fleas is distributed over more plants. Also cropping systems without plowing , with minimal plowing or Herbstsaat can attack by flea beetles with a cooler microclimate reduce within the culture. On fields where canola seed with direct seeding is applied, Erdflohpopulationen are usually smaller. The autumn sowing gives the rape plants the opportunity to germinate before the fleas fly and to reach the 4-leaf stage. In North Dakota , only 4% of the fields that were tilled in the fall had to be treated with insecticides, as opposed to 25% of the fields that were only grown in the spring.
Regular watering can inhibit the development of fleas, but this can promote other diseases and pests. Regular chopping also disturbs the fleas.
Beneficial insects
Various predators are known to feed on earth fleas. These include the larva of the common lacewing ( Chrysoperla carnea ). Only in North America are the ground bug Geocoris bullatus (family Geocoridae ), the beetle Collops vittatus (family Melyridae ), the sickle bug Nabis alternatus and the cricket Gryllus pennsylvanicus of importance . Other beneficial insects such as the brackish wasp species Microtonus vittatae attack fleas, but their parasitization rate is very low. Since the fleas swarm within a narrow time window in spring, it is very difficult for the beneficial insects to combat them effectively.
In the field, however, the control of the coal flea with winged beneficial insects is not very effective because they are very mobile and can easily move away from the infestation sources. Therefore, less agile species, such as nematodes, are more suitable for combating beneficial insects .
Nematodes
A natural antagonist is the species Steinernema carpocapsae , which are distributed in a clay mineral. These nematodes invade the earth flea larvae and then kill them. So that they can develop their full effect, they should be applied at a minimum temperature of 12 ° C and with overcast skies or in the evening, as direct sunlight kills them.
insecticides
One possibility for this are herbal ingredients such as neem oil , Rotenone , Pyrethrine , Veratrine , (for example Sabadill ) and their mixtures, which are recommended for use against fleas.
Catch plants
Field margins with trapping plants such as field radishes or Chinese cabbage that are attractive for fleas can keep the pests away from the cultivated plants. If these are successfully colonized with fleas, these strips can be treated with pesticides. Much of the damage can, however, be achieved by luring the fleas away from the cultivated plants. Plants from the Brassicaceae family are particularly suitable for this, as these are most affected by feeding damage by Phyllotreta cruciferae .
Culture protection nets
Areas previously spared by fleas can be protected against the ingress of pests with culture protection nets. With a maximum mesh size of 0.8 × 0.8 mm, they also protect against cabbage heart midges and whiteflies . However, the changed microclimate can promote other diseases and pests.
literature
- Andrea Oelhafen, Ute Vogler: Ground fleas on cruciferous vegetables; (Phyllotreta spp .; Coleoptera: Chrysomelidae). (= Agroscope Leaflet No. 7). Agroscope, Wädenswil 2014. (PDF)
- K. Mayoori, G. Mikunthan: Damage Pattern of Cabbage Flea Beetle, Phyllotreta cruciferae (Goeze); (Coleoptera: Chrysomelidae) and its Associated Hosts of Crops and Weeds. In: American-Eurasian Journal of Agricultural and Environmental Science. Volume 6, No. 3, 2009, pp. 303-307.
- Nagappan Raja, Geleta Mathewos, Alemayehu Bayable, Tedbabe Nigatu, Zewdinesh Aboset, Birtukan Mulat: Feeding Deterrent Activity of Melia azedarach Linn. and Phytolacca dodecondra (L'Herit) Plant Extracts Against Cabbage Flea Beetle Phyllotreta cruciferae (Goeze). In: Current Research Journal of Biological Sciences. Volume 6, No. 6, 2014, pp. 215-221.
- Gadi VP Reddy, Khanobporn Tangtrakulwanichi, Shaohui Wu, John H. Miller, Victoria L. Ophus, Julie Prewett: Sustainable Management Tactics for Control of Phyllotreta cruciferae (Coleoptera: Chrysomelidae) on Canola in Montana. In: Journal of Economic Entomology. Volume 107, No. 2, 2014, pp. 661-666. doi: 10.1603 / EC13503
- Janet J. Knodel, Denise L. Olson: Crucifer Flea Beetle: Biology and Integrated Pest Management in Canola. Fact Sheet, North Dakota State University, Fargo 2002. (PDF)
- Arved Lompe (after KH Mohr): Determination table of the genus Phyllotreta, in European beetles. Status: September 28, 2013 ( online )