The use of plant growth regulators (PGRs) may negatively influence the outcome of biological control programs, according to research conducted by Sara Prado and Dr. Steven Frank in the Department of Entomology at North Carolina State University.
Prado and Frank have published two research papers that highlight how the use of PGRs affects plant structure, branching, and internal chemical changes within the plant.
In the first paper, “Compact Plants Reduce Biological Control of Myzus persicae by Aphidius colemani.” Prado and Frank noted PGRs can result in compact plants that have more branches and are bushier than untreated plants. Since plant architectural complexity can have strong effects on natural enemy foraging efficiency and pest suppression, their hypothesis was that the use of PGRs would reduce aphid suppression by the parasitic wasp Aphidius colemani. They investigated how the PGR paclobutrazol and A. colemani interact to affect the abundance and behavior of the green peach aphid Myzus persicae. They found that paclobutrazol alone reduced aphid abundance compared to untreated plants. However, when parasitoids were present, paclobutrazol and associated changes in plant architecture reduced parasitism and increased aphid abundance compared to untreated plants.
In the second paper, “Tritrophic Effects of Plant Growth Regulators in an Aphid-Parasitoid System,” Prado and Frank began by noting that PGRs have the potential to negatively affect the outcome of biological control via plant architectural changes and plant chemical changes. In the study, they investigated the effect of four commonly used PGRs on Myzus persicae abundance and suppression, and A. colemani health in a greenhouse experiment. None of the PGRs reduced aphid abundance alone or affected aphid suppression by A. colemani. However, the PGRs had a range of negative effects on parasitoid health. In summary, the study showed PGRs can negatively affect parasitoid health and reduce parasitism, suggesting the potential for negative long-term effects on the efficacy of biological control.