Some thoughts on Thrips palmi
A paper from Dr Vierbergen recalls the spread of Thrips palmi (EPPO A1 quarantine pest) outside its region of origin and gives thoughts on why quarantine measures are necessary to prevent its establishment in Europe.
When comparing the biology of Thrips palmi with Frankliniella occidentalis, it can be noted that T. palmi feeds exclusively on cell liquids whereas F. occidentalis also feeds on pollen. This urges F. occidentalis to look for flowers at a suitable stage and therefore its potential for dispersal seems greater than for T. palmi. It is felt that the very wide host range of T. palmi is insufficiently known. As a general remark, it is stated that thrips species are incidental visitors on many plants but may not be able to complete their life cycle on them. The author felt that interceptions made on orchids in Europe are probably of minor importance because there have never been introductions into the extensive culture of orchids in Europe.
Concerning eradication, it is pointed out that no report on elimination of Thysanoptera after introduction has been made, except for T. palmi from Dutch glasshouses (in 1988 on Cactaceae, in 1992 in 3 Ficus greenhouses, in 1994 and 1995). In the first outbreaks, eradication was achieved with the complete destruction of the plants. In recent findings, eradication was achieved with a combination of insecticides (imidacloprid, carbofuran, dichlorvos, methiocarb). Decrease of thrips populations was monitored with yellow and blue sticky traps during a quarantine period which was calculated as follows:
Tq=2 x Tpupa + 2 x Tegg
Tq = Quarantine period
Tpupa = lifetime pupa + 3 x standard deviation
Tegg= lifetime eggs + 3 x standard deviation
Observations made in the Dutch glasshouses showed that active dispersal of T. palmi was very low. In addition, T. palmi has never been found on traps located in the immediate vicinity of heavily infested glasshouses. Dispersal between glasshouses is ensured by exchange of plant material.
The author stressed that quarantine measures against T. palmi are useful, as at present introduction pressure is not too high and active dispersal within glasshouses is very low. But he is concerned that, in the long term, the situation may change, especially if more parts of the world are invaded by the pest which would greatly increase introduction pressure.
Sources
Vierbergen, G. (1996) After introduction of Frankliniella occidentalis in Europe: prevention of establishment of Thrips palmi (Thysanoptera: Thripidae).
Acta Phytopathologica et Entomologica Hungarica, 31(3-4), 267-273.