Relative humidity controls pupation success and dropping behaviour of western flower thrips, <i>Frankliniella occidentalis</i> (Pergande) (Thysanoptera: Thripidae)

Abstract

Abstract An investigation into relative humidity (RH) requirements for successful pupation of western flower thrips, Frankliniella occidentalis , found that RH greater than 80% was necessary for late‐stage second instars to survive to pupation, with at least 90% RH being optimal. RH also impacted on dropping behaviour of late‐stage larvae to pupate below a leaf surface. The mean RH for the change point for larvae to drop rather than remain on the plant surface was 81.2% (95% confidence interval 77.0%, 86.9%), with lower RH inducing dropping. A change in water relationships within the larva is proposed as the most likely mechanism for determining whether it remains on the plant or drops to pupate. These findings have implications with respect to integrated pest management options, particularly the management of RH in greenhouse situations, whether to target the ground or crop canopy, or choice and placement of biocontrol agents.