Less than two per cent of all thrips species, that means 100 species of the 5000 known species of the order Thysanoptera are accepted as important pest species in agriculture, horticulture and forestry. In the last years 11 species of the Thripidae has increased their importance as effective vectors of tospoviruses. These considerations leads to a different view of modern identification methods followed by the question - which species should go in a key and who will use the key? A modern computerized interactive key should cover a restricted number of species of known economic importance and furthermore, the key should combine classical (Mound et al. 1976, Moritz 1994, Palmer et al. 1989, Mound and Kibby 1998, Moritz et al. 1996, 1998, 1999, 2001, 2004, 2006) and molecular identification methods. This combination saves time and money and allows a quick and correct identification of all ontogenetic stages.
Bunyaviridae -Tospoviruses:
Tospoviruses are the only phytopathogenic genus in a family of vertebrate-infecting viruses, the Bunyaviridae. The genom of this genus consists of three single stranded RNA segments (ssRNA) covered by a lipid envelope which contains two types of glycoproteins. TSWV (Tomato spotted wilt virus) and INSV (Impatiens necrotic spot virus) are important members now distributed world-wide. Like most other plant viruses, Tospovirus transmission is accomplished by some polyphagous thrips species of the subfamily Thripinae (Frankliniella occidentalis).
Virus vector ontogenesis:
Only late second instar larvae and adult thrips can transmit tospoviruses if the virus acquisition occurs during first instar larval feeding on tospovirus infected plants. Less is known about why one species becomes a vector and another ones not, or why is the 1st larval stage the important phase for later virus transmission. Many results of midgut epithelial cells and structurs, entry and escape borders and the role of the visceral muscle cells leads to a deeper understanding of virus acquisition and transmission. Morphogenetic movements during the larval development and the understanding of changes during the metamorphosis give totally new ideas of the virus pathways through its vector (Moritz et al. 2004).
Thysanoptera - Biology:
Thrips belong to the order of insects known as Thysanoptera, meaning fringed wings. About 5000 species are known - and probably there are three times more. Thrips are very small insects and most species are only 1 to 3 mm long. They have evolved a wide rang of life styles using their asymmetric piercing-sucking mouthparts. Thrips feed on fungi, pollen grains, leaf cells or become predators of small insects and mites. Some of them are major crop pests and have the status of quarantine organisms. The reproduction mode is arrhenotoky in which fertilized eggs (diploid eggs) give rise to females and unfertilized eggs to males, or thelytoky in which unfertilized eggs give rise to females (haploid eggs) and males do not occur. Fungus feeding and gall-producing thrips have subsocial to eusocial structures (Crespi 1992, Nature 395: 724-726).
Biocommunication:
Many arthropods use acoustical, chemical and optical signals for interspecific communication. Sometimes sound or vibration is presumably an aposematic signal aimed at discouraging predators from attacking the toxic, armed, or otherwise unpalatable sender. Some insects present acoustical signals together with optical (aposematic coloration) and/or chemical signals (allomones). Female velvet ants (Mutillidae) use all three together to make multimodal signals, but they do not use these signals intraspecific. Some ants (Formicidae) are able to produce similar signals. Mainly they are interpreted as social signals, but possibly they have an interspecific defensive function too.