Abstract:

Plant growth regulators (PGRs) have the potential to negatively affect the outcome of biological control
via plant architectural changes and plant chemical changes. Despite studies demonstrating the negative
effects of PGRs on herbivore survival and development, to date, no studies have investigated the tritrophic effects of PGRs on parasitoid life history traits. In this study we investigated the effect of four commonly used PGRs on Myzus persicae abundance and suppression, and Aphidius colemani fitness in a
greenhouse experiment. None of the PGRs reduced aphid abundance alone or affected aphid suppression
by A. colemani. However, paclobutrazol reduced the number of mummies that developed on plants. PGRs
had a range of negative effects on parasitoid fitness. No adult parasitoids eclosed from mummies on
ancymidol treated plants. Paclobutrazol reduced parasitoid size, and paclobutrazol and uniconazole
reduced female:total ratio. This study shows that PGRs can negatively affect parasitoid fitness, and reduce
parasitism, suggesting the potential for negative long-term effects on the efficacy of biological control.