Bioinsecticide synergy: The good, the bad and the unknown

Synergy between certain conventional chemical insecticides has been known for decades. However, heightened awareness and interest in bioinsecticides (microbials, botanicals and arthropod venoms) have led to numerous studies demonstrating synergy between bioinsecticides and conventional insecticides, between different bioinsecticides, and among specific constituents in botanicals, which are themselves chemically complex. At the same time, bioinsecticides have often been shown to be less deleterious to non-target organisms, particularly natural enemies and pollinators, although they are not entirely without negative impacts. However, the influence of synergy among these compounds, mixtures of bioinsecticides, or combinations of bioinsecticides and conventional insecticides on non-target species remains relatively unexplored. The taxonomic diversity of target (pest) insects for which such synergy has been documented suggests that this action could also occur in non-target species. However, the impact of this synergy on non-targets in actual field conditions remains difficult to predict. • Synergy by bioinsecticides is common against diverse pest arthropods. • It is also common across many modes of action, and appears to be both dose-specific and idiosyncratic. • Synergy can occur between bioinsecticides and conventional ones. • It can also occur between types of bioinsecticides. • Little work has characterized synergy of bioinsecticides in non-target arthropods.