Abstract
Integrated pest management (IPM) tactics may effectively control focal pests, but it is also important to test the compatibility of different tactics, and consider non-target organisms. We investigated the effects of a neonicotinoid seed treatment and Rag resistance genes used for soybean aphid (Aphis glycines Matsumura) control on reproduction of a non-target herbivore (twospotted spider mite, Tetranychus urticae Koch) in short-term greenhouse experiments. We also examined interactions between spider mites and a specialist phytoseiid mite [Ambylseius fallacis (Garman)] and assessed the effects of a co-occurring opportunistic omnivore [Frankliniella occidentalis (Pergande)] by including thrips density as a covariate. There were no interactive or main effects of the presence of Rag genes on the densities of any of the arthropods. Overall, effects of the seed treatment on spider mite densities varied, with no difference when mites were confined in clip cages, and higher populations on seed-treated plants when on whole plants. Predatory mites had a consistent negative impact on spider mites, and densities of A. fallacis immatures were similar between seed treated and non-seed treated plants. However, the relationship between spider mite and thrips densities was different between these two plant types, but only in the clip cage experiment lacking predatory mites. This research highlights the importance of considering how IPM tactics might affect non-target organisms.
Highlights
When attempting to manage arthropods, even within simplified monocultures, management practices targeting one pest can have unforeseen and undesirable consequences on non-target arthropods
The densities of spider mites at the end of the experiment were not affected by the identity of the soybean line, and there was no interactive effect of soybean line and insecticidal seed treatment (ST × Line, df 3,70, F = 0.437, p = 0.727; Line, df 3,70, F = 1.967, p = 0.127)
Even though no thrips were present within clip cages when spider mites were added, at the 12 ± 1.0, end of the experiment thrips were present on 72.5% of plants
Summary
When attempting to manage arthropods, even within simplified monocultures, management practices targeting one pest can have unforeseen and undesirable consequences on non-target arthropods. Using multiple control tactics to combat pests is one of the goals of integrated pest management (IPM) programs, and ideally would lead to synergistic pest control. Well-known examples include non-selective insecticides and resistant host plants interfering with biological control [1,2]. It is important to consider how pest management tactics impact non-target herbivores, which could replace target pests and injure host plants [3,4], or serve a positive role as alternative prey for natural enemies [5]. Obtaining basic information on how relevant organisms are affected by the use of individual and combined management tactics can help develop successful IPM programs
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