Why does biocontrol of some thrips species fail?

Abstract: The aim of our research was to investigate why biocontrol of some thrips species,
such as Echinothrips americanus fails, whereas it works with other species, such as
Frankliniella occidentalis. Many authors reported that several natural enemies showed potential for control of E. americanus with predatory mites under laboratory conditions, but no control in greenhouses. We speculated that this may be caused by differences in defensive behaviour of these two thrips species and investigated this using the predatory mite Amblyseius swirskii. We also included a third, newly invasive thrips species, Thrips parvispinus. We observed the interactions between the predator and both first and second instar larvae of all three thrips species and found that the species and stages differ in the degree to which they show defensive behaviour and its effectiveness, being E. americanus the most effective. We discuss the consequences of these defensive behaviours for effective biocontrol of these thrips.