Residual effect of commonly used fungicides in strawberries on Amblyseius swirskii, Neoseiulus cucumeris, and Neoseiulus californicus (Mesostigmata: Phytoseiidae)

Abstract

Florida's strawberry industry is currently valued at $511 million annually but faces challenges from pathogens and arthropod pests especially Tetranychus urticae Koch (twospotted spider mite) and Scirtothrips dorsalis Hood (chilli thrips). Predatory mites, particularly Neoseiulus cucumeris Oudemans, Neoseiulus californicus McGregor, and Amblyseius swirskii Athias-Henriot, play a crucial role in pest management. However, there are concerns regarding how these biological control agents are affected by fungicides used in current pathogen management strategies. This study assessed the residual effects of commonly used fungicides in strawberries on the survival, feeding, and oviposition of these predatory mites. Commercially sourced predatory mites were reared on S. dorsalis larvae, and gravid female predators placed on fungicide treated strawberry leaf discs in a Munger cell for 120 h. Fungicides tested included two formulations of Captan, hydrogen peroxide + peroxyacetic acid, cyprodinil + fludioxonil, tetramethylthiuram disulfide, cyflufenamid and a control. All fungicides tested had an impact on the survival, feeding, and oviposition of the predators. Among the fungicide treatments, the lowest predator survival was observed in the cyprodinil + fludioxonil treatment, while the highest was observed in the hydrogen peroxide + peroxyacetic acid and tetramethylthiuram disulfide treatments. In all treatments, feeding and oviposition greatly varied among predators; specifically, N. cucumeris and A. swirskii had the lowest prey consumption, while N. californicus had the highest. These findings highlight the potential incompatibility between fungicides and predatory mites and demonstrate the need for the development of a fungicide rotation program tailored to the different susceptibilities of predators to fungicides.

Keywords: Fragaria x ananassa; Scirtothrips dorsalis; Biocontrol; Integrated pest management; Predatory mites; Side effects.

Fig. 1

Survival of A. swirskii, N. californicus, and N. cucumeris exposed to different fungicide treatments over 120 h. Asterisk (*) indicates significant differences in survival among predator species at each individual time point (Tukey’s HSD test: p < 0.05)

Fig. 2

Number of S. dorsalis consumed by A. swirskii, N. californicus and N. cucumeris exposed to different fungicide treatments over time. Asterisk (*) denotes significant differences in prey consumption between the species at each individual time point (Tukey’s HSD test: p < 0.05)

Fig. 3

Number of eggs produced by A. swirskii, N. californicus and N. cucumeris exposed to different fungicide treatments over 120 h. The asterisk (*) indicates significant differences in prey consumption between predators at each individual time point (Tukey’s HSD test: p < 0.05)