Phenology and development of the gorse thrips, Sericothrips staphylinus Haliday (Thysanoptera: Thripidae), a biological control agent for gorse, Ulex europaeus L. (Fabaceae), in Tasmania

A phenology and temperature development study on the gorse thrips, Sericothrips staphylinus, showed it is bivoltine in Tasmania, Australia. The lower development threshold was around 9.3 °C, and egg to adult development required 345 degree days above this temperature. The life cycle of S.staphylinus is closely synchronised with the phenology of its host plant gorse. Mean seasonal numbers of adults were highest in summer. Once new gorse shoots have matured and hardened by the end of summer, the adult population has entered a reproductive diapause. Over-wintering adults resume egg laying towards the end of winter (from mid-late August). Eggs commence hatching in spring at the time new succulent shoot growth is available as a prime food source for the larvae. Sampling of upper, middle and basal sections of gorse bushes over a three year period showed that numbers of juvenile S.staphylinus were significantly higher on the upper sections of the plant where succulent new growth was present in spring and summer. The release of egg laying S.staphylinus adults in early spring is therefore the optimum time to attempt field establishment of this agent. Field surveys for establishment and dispersal are best conducted in summer when adult populations reach maximum densities. S.staphylinus appears typical of a specialised herbivore exploiting a long living woody plant such as gorse, with latent, usually non-eruptive population dynamics and low population densities. Its ability as a biological control agent may therefore be limited.