Spider mite infestations reduceBacillus thuringiensistoxin concentration in corn leaves and predators avoid spider mites that have fed onBacillus thuringiensiscorn

Abstract

Perceived benefits of insecticidal transgenic crops include reduced usage of broad‐based insecticides, and therefore lower risk to non‐target organisms. Numerous studies have documented low or no direct toxicity of Bacillus thuringiensis (Bt)‐derived toxins against non‐target organisms, but there has been less research on (a) effects of secondary pest infestations on Bt expressing in crops and (b) behavioural responses by predators feeding on host arthropods from Bt crops – both topics are investigated in this study. We quantified predation by the obligate spider mite predator Phytoseiulus persimilis of carmine spider mites (Tetranychus cinnabarinus), reared on Bt or non‐Bt corn (Zea mays). Both no‐choice and two‐choice studies were conducted. In addition, we quantified toxin levels in corn leaves with/without spider mite infestation. Under no‐choice conditions, P. persimilis consumed non‐Bt spider mites at a faster rate than Bt spider mites. Under two‐choice conditions, P. persimilis spent more time in the vicinity of non‐Bt spider mites than near Bt spider mites. Corn infested with spider mites exhibited lower toxin levels than non‐infested plants. These results suggest potentially complex interactions among non‐target herbivores, their natural enemies and Bt crops.

The interaction of two-spotted spider mites, Tetranychus urticae Koch, with Cry protein production and predation by Amblyseius andersoni (Chant) in Cry1Ac/Cry2Ab cotton and Cry1F maize

“…For Cry1F and Cry2Ab, 8 days of exposure reduced concentrations relative to no exposure while for Cry1Ac 4 days of exposure led to reduced concentrations. Thus, there is limited support for the findings of Prager et al (2014) relative to changing Cry protein levels in the face of mite infestations, because the protein concentrations did not appear to be clearly related to mite density. Further investigation of this phenomenon may be warranted.…”

“…A recent study found that concentrations of Cry1Ab and Cry3Bb1 proteins in maize leaves were significantly reduced after infestation with T. urticae (Prager et al 2014). However, they did not delineate T. urticae densities on the Bt maize and did not examine the effect of exposure time nor quantify Cry protein concentrations.…”

“…When given a choice between T. urticae that had consumed Cry3Bb-transgenic eggplants and T. urticae from an untransformed control, the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) showed a preference for the non-Bt-eggplant fed prey (Zemková Rovensaká et al 2005). Prager et al (2014) reported that under choice conditions, P. persimilis spent more time in the vicinity of T. cinnabarius that had consumed non-Bt maize when compared to mites that had consumed Bt (Cry1Ab or Cry3Bb1) maize.…”

Field trials to evaluate the effects of transgenic cry1Ie maize on the community characteristics of arthropod natural enemies

“…However, possible non-target effects on natural enemies also must be assessed for new types of Bt maize 26 . Such an assessment includes numerous factors, such as expression rates of the Cry protein in different plant tissues over the growing season, ingestability and susceptibility of natural enemies to the Cry proteins 12 , transfer probabilities of Cry proteins to higher trophic levels 17 , feeding ecology of both herbivores and natural enemies 27 , and influence of Cry proteins on predator behavior 28 .…”

Smart-use of fertilizers to manage spider mites (Acari: Tetrachynidae) and other arthropod pests

“…In a recent study, Prager, Martini, Guvvala, Nansen, and Lundgren (2014), examined the choice feeding behavior of predatory mites and demonstrated that spider mites cultivated on maize plants expressing Bt toxins (Bacillus thuringiensis) were significantly less preferred compared to spider mites cultivated on maize without the Bt toxins. The study by Prager et al (2014) highlights that predatory mites are able to assess the quality of their prey and underscores the importance of more research into the tri-trophic interactions between the nutritional composition of host plants, feeding and development of herbivorous pests, and the performance of natural enemies.…”