thrips as pests unique features classification host range Scope of this work

About tospovirus vectors - thrips-virus-interactions
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There are now about 10 species of thrips known to carry Tospoviruses to a wide range of plants (Mound 1996; Ullman 1996). Only adult thrips that have acquired a virus during their first or early second larval stage can transmit tospoviruses (van de Wetering et al. 1996; Amin et al. 1981, German et al. 1992, Ullman et al. 1991, 1992, 1995)(see photo). The most commonly discussed and the type member of these infections is TSWV (tomato spotted wilt virus).
However, little is known about thrips biology. why one species becomes a vector and others not, and why the first larval stage is the important ontogenetic phase for virus acquisition for subsequent adult transmission. However, examination of morphogenetic movements during ontogenetic development has provided a totally new view of the likely virus pathway through a vector (Moritz et al. 2004)

Frankliniella occidentalis: Larval acquisition and adult transmission of TSWV.
Tospoviruses are transmitted to plants only by adult thrips that have acquired these pathogens from viruliferous plants as larvae (Amin et al. 1981, German et al. 1992, Ullman et al. 1992) (SEM-photo of an oviposited egg into plant tissue, first and second larva, prepupa and pupa and an adult female and male).
Frankliniella occidentalis: Frontal section of a first instar larva showing the association of salivary gland cells, mid gut (part I) cells and visceral muscle cells (SEM und TEM: Immunolabeling of virus proteins in the midgut).
Frankliniella occidentalis: In the first instar larva the small head capsule contains large groups of cibarial muscles (Moritz 1988). These muscle groups displace the supra-oesophageal ganglion far into the thorax, and push the lobed salivary glands against the midgut. Cells of the midgut, the salivary glands and the visceral muscle fibres have an intimate contact. In the late second instar larva, the reposition of the brain into the head capsule begins. During this process the tight cell contact between these tissues disappears. The final separation of the salivary glands and the mid gut is reached after the development of large wing muscle groups (Moritz 1989).
Frankliniella occidentalis: Head of a larva, sagittal section showing mouth cone, nervous system and cibarial muscles. Note the displacement of the brain into the prothoracic region during the first larval stage (sagittal section, HE-staining)
Frankliniella occidentalis: Outline of tospovirus pathways through its vector. The acquisition of tospoviruses is restricted to a well defined time window during the first larva, when a temporary association between mid gut, visceral muscle cells and salivary gland cells occurs. This complex is the result of displacement of the brain into the prothoracic region by enlarged cibarial muscle groups. The loss of this complex leads to a strong input of virus particles into the malpighian tubules via the haemocoel (Moritz et al. 2004).

Frankliniella occidentalis: Pathway of TSWV through its vector during different life stages of the thrips.