The American grapevine leafhopper (Scaphoideus titanus Ball) is a homoptera insect belonging to the Cicadellidae family.
From a systematic point of view, it belongs to the Eukaryota Domain, Animalia Kingdom, Sub-Kingdom Eumetazoa, Bilateria Branch, Phylum Arthropoda, Subphylum Hexapoda, Classe Insecta, Subclass Pterygota, Cohort Exopterygota, Subcoorte Neoptera, Superorder Paraneoptera, Section Rhynchotaidea, Order Rhynchotoidea, Order Rhynchotoidea, Rhynchotoidea order. Auchenorrhyncha, Infraorder Cicadomorpha, Superfamily Membracoidea, Family Cicadellidae, Subfamily Deltocephalinae and therefore to the genus Scaphoideus and to the species S. titanus.
Geographical Distribution and Habitat –
The American grapevine leafhopper is an insect originating in North America and accidentally introduced to Europe in the 1960s, probably through wintering eggs in the rhytidome of cuttings, although it was probably already present for some time, following massive imports, during the second half from 1800, of American rootstocks resistant to phylloxera.
In Italy it was first reported in 1963 in Liguria from where it then spread to the northern and central regions of Italy and subsequently to Switzerland, Slovenia, Croatia, Portugal, Spain, Serbia.
The buzzer performs its biological cycle exclusively on the vine, Vitis spp and is the vector of the golden flavescence of the vine.
The eggs of Scaphoideus titanus are recognized for their reniform shape, compressed laterally, transparent and about 1 mm long, initially pearly in color, tend to yellow the end of the embryonic development when the eyes of the embryo, red in color, become visible through the corium. This are located in the wood is very difficult to locate in the field.
This insect has 5 juvenile ages, similar in shape, divided into two stages of neanid without wing sketches and three of nymph with wing sketches present.
The first three ages have a cream-white color, while the nymphs of the fourth age have the characteristic brown areas on the abdomen.
The nymphs of V age are well recognizable thanks to the large ocher areas on the urotergites and the brownish color of the wing cases.
In all ages, the last uritis has two rhomboid black spots. This characteristic differentiates the juvenile forms of Scaphoideus titanus from those of similar species.
The adults measure 5–6 mm in length, with the females slightly larger than the males, and are of an ocher brown color.
The head is triangular froma and on this, both in adults and in youthful forms, there are 2–4 darker transversal bands on the forehead, and a transverse triangular spot located in a dorsal position between the compound eyes.
The legs are cream-colored, except for the metathoracic which have the distal part and the second dark tarsomer, and the first and second whitish tarsomer.
The metathoracic wings are brownish in color and have dark veins; on the front there are white areolas.
The female can be recognized in that she is equipped with a sturdy golden brown ovipositor which allows her to lay her eggs in the branches. This ovipositor, placed at the end of the abdomen, is preceded by a black ring on the pre – genital segment.
Aptitude and biological cycle –
The biological cycle of this insect begins with the laying of eggs which takes place from August to October in the rhytidome of the branches where, around the middle of May, the hatching of the eggs begins, which lasts for several weeks.
The development of the insect occurs through two neanid stages and three nymph stages.
The first age nymphs reach the maximum numerical density in mid-June and subsequently decrease in favor of the pre-imaginary forms of subsequent ages. The presence of youth forms continues for the entire month of July.
The first adults are in early July.
In this way the Scaphoideus titanus performs only one annual generation.
Ecological role –
The American grapevine leafhopper is an insect that can be present in all wine-growing areas, especially the marginal areas, where there is a high presence of small marginal plots or Vitis sp. Plants. restless in the uncultivated
This insect is of negligible importance for direct damage, but it raises serious concerns about the spread of the golden flavescence phytoplasma. The insect becomes infected by pricking the phloem of infected vines and becomes able to transmit the phytoplasma after about a month of incubation. During this period the phytoplasma is localized in the salivary glands of the buzzer which then remains infectious for life.
The direct damages caused by this insect are minor and due to the toxic action of saliva, exercised during the sucking of the sap.
Necrosis and chromatic alterations can be observed on the affected plants, mainly on the ribs and on the buds. The most serious damage, however, is, as mentioned, the indirect damage due to the persistent transmission of the phytoplasma of the golden Flavescence which is localized in the phloem following sucking punctures.
The containment of this insect is basically preventive.
The use of nursery material from areas colonized by the insect must be avoided, because it could contain the eggs of the scaphoid inside.
The fight interventions are aimed at reducing insect populations and eliminating them before they become infected and therefore able to transmit the golden flavescence.
We recommend monitoring the juvenile and adult forms using yellow chromotropic traps.
Adult sampling is therefore important to determine the appropriate time to intervene.
In this case, 3 – 4 traps are used for each hectare of vineyard; the ideal is to place one trap every 6 rows, but for large plots one trap every 10 rows is sufficient. We also recommend placing the traps along a hypothetical diagonal of the vineyard itself.
The positioning period of the traps must take place before the flight of the adults, that is, approximately from the second decade of June, and must be replaced every 10 – 15 days until the end of October.
The identification of the adults of Scaphoideus titanus can be carried out with the naked eye or with the aid of a lens, while to distinguish the sex of the adults caught it is necessary to use a stereomicroscope.
A sampling method can also be carried out with an entomological mowing net, which allows to capture live insects to be subjected to any laboratory diagnosis. It must be used directly on the crown of the vine by beating the vegetation from the bottom up or laterally. With respect to traps, the net provides data not over a period of time but relative to a given day.
For the containment of Scaphoideus titanus it must be carried out, possibly with integrated organic farming techniques, even if this technique is, at the moment, particularly difficult as the only active ingredients allowed active against Scaphoideus titanus are azadiractin, pyrethrum and, to a lesser extent, rotenone.
For this reason, to improve the action of the pyrethrins it is appropriate to implement some precautions:
– carry out the treatments after sunset, as the pyrethrins are degraded by ultraviolet rays;
– use products based on pyrethrins added with piperonyl butoxide which increases its stability;
– dilute the pyrethrum-based product in non-calcareous waters (pH less than 7, ideal between 6 and 6.5), possibly acidifying the water with vinegar or citric acid, as the effect of the pyrethrum is neutralized by basic solutions;
– intervene on the juvenile stages (neanids of I and II age), less mobile and more sensitive, repeating the interventions at a distance of 7 – 10 days, given the scaling of the hatching of the eggs and the low persistence of the pyrethrins;
– wet the basal layer of vegetation well, including the lower leaf page, where the juvenile stages of the buzzer are concentrated.
The struggle with biological methods is not effective, however, if we do not adopt supplementary criteria based on agroecology models (biodiversity of crops, associations with other species, introduction of its antagonists, etc.).
Among the antagonists of this insect we mention: the driinid hymenoptera Gonatopus peculiaris, Lonchodryinus flavus, Esagonatopus perdbilis, Esagonatopus niger and Anteon masoni. These seem to play the main role as parasitoids. Among the other parasitoids are the mimarid hymenoptera and the pipunculid diptera.
The use of chemical control must be the last remedy as the treatment with insecticides then alters the biocoenosis of the entire area with consequences that are worse than the remedy.
In general, the chemical control is carried out taking into consideration the characteristics and methods of acquisition of the infectious power by the insect. In order to transmit the phytoplasm of the golden flavescence, Scaphoideus titanus must feed for 7-8 days on sick plants and spend an incubation period of 30 – 35 days.
The first treatments are thus carried out 30 days after the first births (indicatively in the second decade of June), a period during which the III age nymphs are potentially infectious. Given the scalarity of the births, a second treatment is carried out 20 – 30 days later, while a possible third treatment carried out in late July – early August for precautionary purposes is useful to avoid the arrival of adults from adjacent vineyards not subjected to chemical treatments. It is also recommended to remove suckers after the first treatment. The American vine shoots from the rootstock in fact, can be infected by the golden flavescence but do not manifest the symptoms, thus becoming a possible source of inoculation.
If, on the other hand, it is necessary to intervene with juvenile forms (between I and III age), growth-regulating insecticides such as Flufenoxuron, Buprofezin and Indoxacarb are recommended. On juvenile forms in III and IV age (approximately 35 days after hatching of the eggs) phosphorganic insecticides such as Chlorpyrifos-ethyl, Chlorpyrifos – methyl and Fenitrotion can be used. These active ingredients are also effective against the other buzzers of the vine; fenitrotion and chlorpyrifos – ethyl are also effective against floury mealybugs.
Finally, please note that Ministerial Decree no. 32442 of 31 May 2000, “Measures for the mandatory fight against the Golden Flavescence of the vine” published in the Official Gazette no. 159 of 10 July 2000, established the mandatory fight against the scaphoid throughout Italy, in order to avoid the spread of golden flavescence.
– Wikipedia, the free encyclopedia.
– Russo G., 1976. Agricultural entomology. Special Part. Liguori Editore, Naples.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.