Biological control of the Japanese flower thrips Thrips setosus Moulton (Thysanoptera: Thripidae) in greenhouse ornamentals

Abstract: Recently, the Japanese flower thrips Thrips setosus has been invading some European ornamentals. This plant-feeder and virus-vector was first detected in Europe (in the Netherlands) in autumn 2014 where it spread mostly in cut flowers and potted plants of Hydrangea. Thrips setosus has not been categorized as an invasive pest species and no official specific measures have been taken in countries where the pest has been signaled. Sprays with abamectine, spinosad and azadirachtine are therefore usually performed to prevent any further spread of the thrips. Predatory mite species, even if they are established in the crop, are failing to control this pest. Investigations on effective natural enemies are lacking. Release strategies with the green lacewing Chrysoperla carnea or Chrysoperla carnea combined with the predatory thrips Franklinothrips vespiformis were thus tested in a commercial greenhouse. The green lacewings significantly controlled the pest when they were repeatedly released alone or in combination with predatory thrips. They reduced the thrips populations by a factor nine to less than 0.14 thrips per Hydrangea leaf by July, guaranteeing that leaf and flower damage was negligible. In the present study lacewings and predatory thrips show potential as biocontrol agents of T. setosus.