Characterizing indirect prey-quality mediated effects of a Bt crop on predatory larvae of the green lacewing, Chrysoperla carnea

Azotobacter inoculation can enhance the resistance of Bt cotton to cotton bollworm, Helicoverpa armigera

The rising trend in the cultivation of Bacillus thuringiensis (Bt) transgenic crops may cause a destabilization of agroecosystems, thus increasing concerns about the sustainability of Bt crops as a valid pest management method. Azotobacter can be used as a biological regulator to increase environmental suitability and improve the soil nitrogen utilization efficiency of crops, especially Bt cotton. A laboratory test investigated effects on the development and food utilization of Helicoverpa armigera fed with different Cry1Ab/Cry1Ac proteins and nitrogen metabolism-related compounds from cotton (transgenic variety SCRC 37 vs non-Bt cotton cv. Yu 2067) inoculated with Azospirillum brasilense (Ab) and Azotobacter chroococcum (Ac). The findings indicate that inoculation with Azotobacter significantly decreased the partial development and food utilization indexes (pupal weight; pupation rate; adult longevity; fecundity; relative growth rate, RGR; efficiency of conversion of digested food, ECD; and efficiency of conversion of ingested food, ECI) of H. armigera fed on Bt cotton, but contrasting trends were found among these indexes in H. armigera fed on non-Bt cotton inoculated with Azotobacter, as a result of differences in Bt toxin production. Overall, the results showed that inoculation with Azotobacter had negative effects on the development and food utilization of H. armigera fed on Bt cotton, leading to enhanced target insect resistance. Presumably, Azotobacter inoculation can be used to stimulate plant soil nitrogen uptake to increase nitrogen metabolism-related compounds and promote plant growth for Bt and non-Bt cotton, simultaneously raising Bt protein expression and enhancing resistance efficacy against cotton bollworm in Bt cotton.

Bacillus thuringiensis-based bioinsecticides affect predation of Euborellia annulipes on diamondback moth larvae

Interactions between earwigs and entomopathogens, such as Bacillus thuringiensis (Bt), are still poorly understood. This study tested whether Bt-based bioinsecticides have any effect on the predation of Euborellia annulipes (Lucas) (Dermaptera: Anisolabididae) on Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the pests with the largest number of cases of use and resistance to Bt. Fourth instar larvae were Bt infected by feeding on collard green leaves treated with Dipel®WG and XenTari®WG at the manufacturer-recommended doses. We used one no-choice condition, in which the predator had access to uninfected or Bt-infected larvae separately, and four free-choice conditions: uninfected vs Dipel®-infected larvae, uninfected vs XenTari®-infected larvae, Dipel®-infected vs XenTari®-infected larvae, and uninfected vs Bt-infected larvae with both bioinsecticides. Uninfected larvae were less consumed than those infected by both Bt-bioinsecticides in the no-choice condition. There was a higher consumption of uninfected over Dipel®-infected larvae in the free-choice condition. Overall, uninfected larvae were preferred over both Bt-based bioinsecticides infected larvae. We also used six different prey densities. The ringlegged earwig's predation rate enhanced as the prey population density increased, but the functional response was not affected by Bt-infection, being type II. The predator invested a low amount of handling time on Bt-fed prey and increased the maximum predation rate. Bt-based bioinsecticides cause effects on E. annulipes predation by altering their feeding preference and some aspects of its predatory behavior. The results of our study provide an important background for understanding interactions between earwigs and Bt. In addition, they can be used for decision making during approaches to integrated P. xylostella management.

Different maize varieties have greater impact on Tetranychus urticae (Acari: Tetranychidae) than GE maize expressing Cry3Bb1 insecticidal protein

Genetically engineered (GE) maize expressing Bacillus thuringiensis Cry3Bb1 protein was developed to control Diabrotica spp. (Coleoptera: Chrysomelidae). However, Cry proteins have been reported to have effects on non-target arthropods. We therefore investigated whether the non-target pest Tetranychus urticae (Acari: Tetranychidae) was negatively affected by GE maize expressing the insecticidal Cry3Bb1 protein. Five treatments were used in the laboratory tests to determine the life history parameters of T. urticae on leaves of field-grown maize varieties: (1) GE maize MON 88017, (2) isogenic maize, (3) isogenic maize protected with the soil applied insecticide chlorpyrifos (Dursban 10G), and two unrelated varieties (4) Kipous and (5) PR38N86. Newly emerged T. urticae larvae were individually released on the upper surface of leaf discs placed on water saturated cotton wool. Immatures and adults survival, duration of developmental stages and female fecundity were recorded daily until T. urticae died. Age-stage, two-sex life table method and test for trends, revealed no significant differences in 13 of 18 studied parameters. The unrelated varieties Kipous and PR38N86 on one side and maize with the same genetic background, namely GE maize and isogenic maize with or without insecticide protection, on the other side, showed significant variations in male longevity, larval survival rate, preoviposition period, and fecundity. In addition to the differences between varieties, GE maize and insecticide-protected isogenic maize showed a substantial difference in age-specific fecundity, but not in the mean number of eggs laid by females. The obtained results do not indicate that consumption of Cry3Bb1 has negative effect on T. urticae and suggest that GE maize does not pose a risk with respect to the non-target mite pest T. urticae. The results may have implications for the approval and renewal of import and cultivation for GE crop in the European Union.

No bioaccumulation of Cry protein in the aphidophagous predator Harmonia axyridis

The uptake of insecticidal Cry1Ab from genetically engineered (GE) maize, via herbivore Rhopalosiphum padi, to a predator Harmonia axyridis and its potential intergenerational transfer were investigated. Cry1Ab concentration was found to be 400-fold lower in R. padi compared to GE maize, and more than two-fold lower in H. axyridis. For 62% of H. axyridis samples, Cry1Ab was under the limit of detection (LOD), for another 13% were under the limit of quantification (LOQ). The concentration of Cry1Ab was similar between H. axyridis exposed short-term and long-term with the exception of adults after long-term. There was no correlation between Cry1Ab in females and eggs and neonates. The performance of H. axyridis was comparable between Cry1Ab and control. Histological investigation did not show any pathological changes in the digestive and reproductive systems. The detected route of exposure is unlikely to be important for functional biological control by H. axyridis in agroecosystem.

Effect of Transgenic Cotton Expressing Bt Cry1Ac or Cry1Ab/Ac Toxins on Lacewing Larvae Mediated by Herbivorous Insect Pests

A simple food chain (plant, insect pests, and predatory arthropods) in an agro-ecosystem was set up here as a model system to elucidate the potential effect of transgenic Bacillus thuringiensis (Bt) cotton on non-target organisms. The system included transgenic/non-transgenic cotton, neonate larvae of three herbivorous insects (Spodoptera exigua, Helicoverpa armigera, and S. litura), and predatory lacewing larvae (Chrysopa spp.), which represent the first, second, and third trophic levels, respectively. The results showed that transgenic treatments and different densities of prey had significant effects on both body-weight gain of neonate herbivorous larvae and the number of prey captured by lacewing larvae, respectively. It was found that Bt toxin could persist at the third trophic level in lacewing larvae. The diet mixture bioassay showed that body-weight gain of lacewing larvae was significantly affected by various treatments, especially at lower concentrations of plant-expressed Bt toxin in the diet mixture, which caused significant decreases in body-weight gain. In contrast, synthetic Bt toxin at higher concentrations in the diet did not show this effect. Thus, we inferred that Bt toxin indirectly affected the growth of the lacewings and the lacewings may not be susceptible to Bt toxin or are able to metabolize it.

AMF Inoculation Can Enhance Yield of Transgenic Bt Maize and Its Control Efficiency Against Mythimna separata Especially Under Elevated CO2

The promotion and application of transgenic Bt crops provides an approach for the prevention and control of target lepidopteran pests and effectively relieves the environmental pressure caused by the massive usage of chemical pesticides in fields. However, studies have shown that Bt crops will face a new risk due to a decrease in exogenous toxin content under elevated carbon dioxide (CO2) concentration, thus negatively affecting the ecological sustainability of Bt crops. Arbuscular mycorrhizal fungi (AMF) are important beneficial microorganisms that can effectively improve the nutrient status of host plants and are expected to relieve the ecological risk of Bt crops under increasing CO2 due to global climate change. In this study, the Bt maize and its parental line of non-transgenic Bt maize were selected and inoculated with a species of AMF (Funneliformis caledonium, synonyms: Glomus caledonium), in order to study the secondary defensive chemicals and yield of maize, and to explore the effects of F. caledonium inoculation on the growth, development, and reproduction of the pest Mythimna separata fed on Bt maize and non-Bt maize under ambient carbon dioxide concentration (aCO2) and elevated carbon dioxide concentration (eCO2). The results showed that eCO2 increased the AM fungal colonization, maize yield, and foliar contents of jasmonic acid (JA) and salicylic acid (SA), but decreased foliar Bt toxin content and Bt gene expression in Bt maize leaves. F. caledonium inoculation increased maize yield, foliar JA, SA contents, Bt toxin contents, and Bt gene expression in Bt maize leaves, and positively improved the growth, development, reproduction, and food utilization of the M. separata fed on non-Bt maize. However, F. caledonium inoculation was unfavorable for the fitness of M. separata fed on Bt maize, and the effect was intensified when combined with eCO2. It is indicated that F. caledonium inoculation had adverse effects on the production of non-Bt maize due to the high potential risk of population occurrence of M. separata, while it was just the opposite for Bt maize. Therefore, this study confirms that the AMF can increase the yield and promote the expression levels of its endogenous (JA, SA) and exogenous (Bt toxin) secondary defense substances of Bt maize under eCO2, and finally can enhance the insect resistance capacity of Bt crops, which will help ensure the sustainable utilization and safety of Bt crops under climate change.

Transgenic Cry1Ac/CpTI cotton assessment finds no detrimental effects on the insect predator Chrysoperla sinica

The widespread commercialization of genetically modified (GM) cotton makes it important to assess the potential impact of this recombinant crop on non-target organisms. As important natural enemies of cotton field predators, green lacewing Chrysoperla sinica larvae are exposed to Bt insecticidal proteins expressed by GM cotton by feeding on herbivorous pests, and adults are directly exposed to Bt proteins by cotton pollen consumption. However, potential impacts of transgenic Bt cotton on C. sinica remain unclear. In this study, we evaluated the effects of two transgenic cotton varieties, CCRI41 and CCRI45, which express Cry1Ac (Bt toxin) and CpTI (Cowpea Trypsin Inhibitor), on C. sinica larvae and adults. After being fed with cotton aphids Aphis gossypii reared on transgenic cotton, the survival rate, developmental duration, pupation rate, and emergence rate of larvae were not adversely affected. After being fed two types of transgenic cotton pollen, the 7-day weight of adults and the preoviposition period and the cumulative oviposition of females were not significantly different from control specimen. Taken together, these results indicate that the potential risks of the two tested GM cotton varieties for the predator C. sinica are negligible. CAPSULE: Our study indicated that GM cotton varieties CCRI41 and CCRI45 have no adverse effects on insect predator C. sinica.

Efficiency of biological control for fall armyworm resistant to the protein Cry1F

Understanding the ecological and toxicological relationship between genetically modified cultivars (GM) and biological control agents is of great importance for discussions related to the compatability of GM cultivars and integrated management strategies for pest resistance. The present study evaluated the search behavior and predatory capacity of Orius insidiosus (Say) (Hemiptera: Anthocoridae) and Doru luteipes (Scudder) (Dermaptera: Forficulidae) on eggs and caterpillars of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) resistant or not to the protein Cry1F expressed in Bt corn. To determine the search time, a stopwatch was run until the capture of the first prey, predation capacity was evaluated by counting the prey remaining after 24 hours of infestation. The injuries of S. frugiperda in genetically modified and conventional corn in the presence and absence of predators was also evaluated. The predators were not able to distinguish between resistant and susceptible prey (eggs or caterpillars), given the predatory behaviour observed. There was no difference in searching time or predatory capacity between the predators for eggs and caterpillars of either resistant or susceptible S. frugiperda. In the presence of predators, the injury scores for resistant S. frugiperda on the Bt corn plants were lower. It was concluded that O. insidiosus and D. luteipes did not notice the presence of the protein Cry1F in the prey S. frugiperda, which may facilitate the combined use of GM corn and biological control in integrated management programs and for management of pest resistance.

Arbuscular mycorrhizal fungi alter the food utilization, growth, development and reproduction of armyworm (Mythimna separata) fed on Bacillus thuringiensis maize

BACKGROUND

The cultivation of Bt maize (maize genetically modified with Bacillus thuringiensis) continues to expand globally. Arbuscular mycorrhizal fungi (AMF), an important kind of microorganism closely related to soil fertility and plant nutrition, may influence the ecological risk of target lepidopteran pests in Bt crops.

METHODS

In this study, transgenic Bt maize (Line IE09S034 with Cry1Ie vs. its parental line of non-Bt maize cv. Xianyu335) was inoculated with a species of AMF, Glomus caledonium (GC). Its effects on the food utilization, reproduction and development of armyworm, Mythimna separata, were studied in a potted experiment from 2017 to 2018.

RESULTS

GC inoculation increased the AMF colonization of both modified and non-modified maize, and also increased the grain weight per plant and 1,000-grain weight of modified and non-modified maize. However, the cultivation of Bt maize did not significantly affect the AMF colonization. The feeding of M. separata with Bt maize resulted in a notable decrease in RCR (relative consumption rate), RGR (relative growth rate), AD (approximate digestibility), ECD (efficiency of conversion of digested food) and ECI (efficiency of conversion of ingested food) parameters in comparison to those observed in larvae fed with non-Bt maize in 2017 and 2018, regardless of GC inoculation. Furthermore, remarkable prolongation of larval life span and decreases in the rate of pupation, weight of pupa, rate of eclosion, fecundity and adult longevity of M. separata were observed in the Bt treatment regardless of GC inoculation during the two-year experiment. Also, when M. separata was fed with Bt maize, a significant prolongation of larval life and significant decreases in the pupal weight, fecundity and adult longevity of M. separata were observed when inoculated with GC. However, it was just the opposite for larvae fed with non-Bt maize that was inoculated with GC. The increased percentage of larval life-span, the decreased percentages of the food utilization, and the other indexes of reproduction, growth, and development of M. separata fed on Bt maize relative to non-Bt maize were all visibly lower when under GC inoculation in contrast to the CK.

DISCUSSION

It is presumed that Bt maize has a marked adverse impact on M. separata development, reproduction and feeding, especially when in combination with the GC inoculation. Additionally, GC inoculation favors the effectiveness of Bt maize against M. separata larvae by reducing their food utilization ability, which negatively affects the development and reproduction of the armyworm. Thus, Bt maize inoculated with AMF (here, GC) can reduce the severe threats arising of armyworms, and hence the AMF inoculation may play an important ecological functions in the field of Bt maize ecosystem, with potentially high control efficiency for the target lepidopteran pests.

Transgenic Cry1Ac cotton does not affect the development and fecundity of Chrysoperla carnea

The development and fecundity of the predator Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) were assessed by feeding Aphis gossypii Glover (Hemiptera: Aphididae) that had been reared on transgenic Bacillus thuringiensis (Bt) cotton SGK321 and a non-Bt cotton control (SY321) for two successive generations. We found no significant differences in the developmental stage duration, stage survival, or egg hatch rate between C. carnea fed A. gossypii reared on the Bt and non-Bt cotton. The fecundity per female over a 25-day observation period was very similar between treatments; for C. carnea fed A. gossypii reared on SGK321 vs. SY321, the amount of eggs laid was not significantly different in both generations. Furthermore, a population dynamics of A. gossypii and lacewing (mainly C. carnea) were highly similar in the SGK321 and SY321 treatments during 2016–2017. These results suggest that Bt cotton does not have a significantly negative or positive effect on C. carnea in terms of development, survival, fecundity, or population dynamics.

Does prey encounter and nutrient content affect prey selection in wolf spiders inhabiting Bt cotton fields?

Wolf spiders are abundant and voracious predators at the soil-plant interface in cotton crops. Among other prey, they attack late-instar larvae of the cotton bollworm Helicoverpa spp., an economically important pest. Consequently, wolf spiders in transgenic Bt cotton could provide significant biological control of Bt-resistant Helicoverpa larvae that descend to the soil to pupate. The predator-prey interactions between wolf spiders and Helicoverpa could, however, be constrained by the presence of alternative prey and intraguild predators. This study used laboratory enclosures to analyse the effect of alternative prey on predatory selection of the wolf spider Tasmanicosa leuckartii Thorell. The prey included another wolf spider Hogna crispipes Koch (potential intraguild predator), the ground cricket Teleogryllus commodus Walker (minor pest), and Helicoverpa armigera larvae (major pest). We tested if encounter rates, prey vulnerability, and prey nutritional content influenced the likelihood that a prey was attacked. In three-way food webs, Tasmanicosa encountered and attacked Teleogryllus and Helicoverpa in similar frequencies. However, in the presence of a competing intraguild predator and potential prey (Hogna) in a four-way food web, Tasmanicosa did not always attack Teleogryllus at first encounter, but still attacked Helicoverpa at each encounter. Helicoverpa (protein-poor) and Hogna (protein-rich) were consumed by Tasmanicosa in similar proportions, suggesting that Tasmanicosa might benefit from nutrient balance as an outcome of diverse prey in this food web. As Teleogryllus (protein rich) escapes quicker than Helicoverpa and Hogna, Hogna may be an easier protein-rich option than Teleogryllus. Field surveys showed that while Teleogryllus was the most common prey, wolf spiders feed on diverse insect taxa, as well as other spiders. That Tasmanicosa readily attacked Helicoverpa larvae in the presence of alternative prey is an encouraging result that supports the potential of Tasmanicosa predation to assist in the control of Bt-resistant Helicoverpa larvae and thereby inhibit the proliferation and spread of resistance.

Transfer of Cry1Ac and Cry2Ab proteins from genetically engineered Bt cotton to herbivores and predators

With the cultivation of Bt cotton, the produced insecticidal Cry proteins are ingested by herbivores and potentially transferred along the food chain to natural enemies, such as predators. In laboratory experiments with Bollgard II cotton, concentrations of Cry1Ac and Cry2Ab were measured in Lepidoptera larvae (Spodoptera littoralis, Heliothis virescens), plant bugs (Euschistus heros), aphids (Aphis gossypii), whiteflies (Bemisia tabaci), thrips (Thrips tabaci, Frankliniella occidentalis), and spider mites (Tetranychus urticae). Tritrophic experiments were conducted with caterpillars of S. littoralis as prey and larvae of ladybird beetles (Harmonia axyridis, Adalia bipunctata) and lacewings (Chrysoperla carnea) as predators. Immunological measurements (ELISA) indicated that herbivores feeding on Bt cotton contained 5%-50% of the Bt protein concentrations in leaves except whiteflies and aphids, which contained no or only traces of Bt protein, and spider mites, which contained 7 times more Cry1Ac than leaves. Similarly, predators contained 1%-30% of the Cry protein concentration in prey. For the nontarget risk assessment, this indicates that Bt protein concentrations decrease considerably from one trophic level to the next in the food web, except for spider mites that contain Bt protein concentrations higher than those measured in the leaves. Exposure of phloem sucking hemipterans is negligible.

Influence of elevated CO2 on development and food utilization of armyworm Mythimna separata fed on transgenic Bt maize infected by nitrogen-fixing bacteria

BACKGROUND

Bt crops will face a new ecological risk of reduced effectiveness against target-insect pests owing to the general decrease in exogenous-toxin content in Bt crops grown under elevated carbon dioxide (CO2). The method chosen to deal with this issue may affect the sustainability of transgenic crops as an effective pest management tool, especially under future atmospheric CO2 level raising.

METHODS

In this study, rhizobacterias, as being one potential biological regulator to enhance nitrogen utilization efficiency of crops, was selected and the effects of Bt maize (Line IE09S034 with Cry1Ie vs. its parental line of non-Bt maize Xianyu 335) infected by Azospirillum brasilense (AB) and Azotobacter chroococcum (AC) on the development and food utilization of the target Mythimna separate under ambient and double-ambient CO2 in open-top chambers from 2016 to 2017.

RESULTS

The results indicated that rhizobacteria infection significantly increased the larval life-span, pupal duration, relative consumption rate and approximate digestibility of M. separata, and significantly decreased the pupation rate, pupal weight, adult longevity, fecundity, relative growth rate, efficiency of conversion of digested food and efficiency of conversion of ingested food of M. separata fed on Bt maize, while here were opposite trends in development and food utilization of M. separata fed on non-Bt maize infected with AB and AC compared with the control buffer in 2016 and 2017 regardless of CO2 level.

DISCUSSION

Simultaneously, elevated CO2 and Bt maize both had negative influence on the development and food utilization of M. separata. Presumably, CO2 concentration arising in future significantly can increase their intake of food and harm to maize crop; however, Bt maize infected with rhizobacterias can reduce the field hazards from M. separata and the application of rhizobacteria infection can enhance the resistance of Bt maize against target lepidoptera pests especially under elevated CO2.

Bt Proteins Have No Detrimental Effects on Larvae of the Green Lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Biosafety of a genetically modified crop is required to be assessed prior to its commercialization. For this, a suitable artificial diet was developed and used to establish a dietary exposure test for assessing the toxicity of midgut-active Bt insecticidal proteins on Chrysopa pallens (Rambur). Subsequently, this dietary exposure test was used to evaluate the toxicity of the proteins Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, and Vip3Aa on C. pallens larvae. Temporal stability, bioactivity, and the intake of the insecticidal proteins were confirmed by enzyme-linked immunosorbent assay and a sensitive-insect bioassay. The life history characteristics, such as survival, pupation, adult emergence, 7-day larval weight, larval developmental time, and emerged male and female fresh weights remained unaffected, when C. pallens were fed the pure artificial diet (negative control) and the artificial diets containing 200 μg/g of each purified protein: Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, or Vip3Aa. On the contrary, all of the life history characteristics of C. pallens larvae were adversely affected when fed artificial diet containing boric acid (positive control). The results demonstrate that diets containing the tested concentrations of Cry1Ab, Cry1Ac, Cry1Ah, Cry1Ca, Cry1F, Cry2Aa, Cry2Ab, and Vip3Aa have null effects on C. pallens larvae. The outcome indicates that genetically modified crops expressing the tested Bt proteins are safe for the lacewing, C. pallens.

Does Bt maize expressing Cry1Ac protein have adverse effects on the parasitoid Macrocentrus cingulum (Hymenoptera: Braconidae)?

The potential effects of insect-resistant, genetically engineered (GE) crops on non-target organisms, especially on predators and parasitoids, must be evaluated before their commercial cultivation. The effects of GE maize that produces Cry1Ac toxin on the parasitoid Macrocentrus cingulum were assessed by direct bioassay and indirect bioassay. In the indirect bioassay, parasitism rate, cocoon weight and the number of M. cingulum progeny produced per host were significantly reduced when M. cingulum-parasitized Cry1Ac-susceptible Ostrinia furnacalis were fed a diet containing purified Cry1Ac; however, life-table parameters of M. cingulum were not adversely affected when the same assay was performed with Cry1Ac-resistant O. furnacalis. These results indicated that the detrimental effects detected with a Cry1Ac-susceptible host were mediated by poor host quality. In a direct bioassay, no difference in life-table parameters were detected when M. cingulum adults were directly fed a 20% honey solution with or without Cry1Ac; however, survival and longevity were significantly reduced when M. cingulum adults were fed a honey solution containing potassium arsenate, which was used as a positive control. The stability and bioactivity of Cry1Ac toxin in the food sources and Cry1Ac toxin uptake by the host insect and parasitoid were confirmed by enzyme-linked immunosorbent assay and sensitive-insect bioassays. Our results demonstrate that M. cingulum is not sensitive to Cry1Ac toxin at concentrations exceeding those encountered in Bacillus thuringiensis maize fields. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms and will be useful for assessing other non-target impacts.

Predator Preference for Bt-Fed Spodoptera frugiperda (Lepidoptera: Noctuidae) Prey: Implications for Insect Resistance Management in Bt Maize Seed Blends

Understanding indirect, trophic-level effects of genetically engineered plants, expressing insecticidal proteins derived from the bacterium, Bacillus thuringiensis (Bt), is essential to the ecological risk assessment process. In this study, we examine potential indirect, trophic-level effects of Bt-sensitive prey using the predator, Harmonia axyridis (Pallas), feeding upon Spodoptera frugiperda (J.E. Smith) larvae, which had delayed development (lower body mass) following ingestion of Cry1Ab maize leaves. We found no adverse effects on development and survival when H. axyridis larvae were fed S. frugiperda larvae that had fed on Cry1Ab maize tissue. Presence of Cry1Ab in H. axyridis decreased considerably after switching to another diet within 48 h. In a no-choice assay, H. axyridis larvae consumed more Bt-fed S. frugiperda than non-Bt-fed larvae. Preference for S. frugiperda feeding on Bt maize was confirmed in subsequent choice assays with H. axyridis predation on Bt-fed, 1-5-d-old S. frugiperda larvae. We suggest that H. axyridis preferred prey, not based on whether it had fed on Bt or non-Bt maize, but rather on larval mass, and they compensated for the nutritional deficiency of lighter larvae through increased consumption. Pest larvae with variable levels of resistance developing on Bt diet are often stunted versus sensitive larvae developing on non-Bt diet. It is possible that such larvae may be preferentially removed from local field populations. These results may have implications for insect resistance management and may be played out under field conditions where seed blends of Bt and non-Bt hybrids are planted.

The Potential Effect of Bt Maize on Chrysoperla pudica (Neuroptera: Chrysopidae)

Previous studies into third trophic level exposure of Chrysoperla spp. (Neuroptera: Chrysopidae) to Cry1Ab proteins produced by Bt crops yielded contradicting results. These contradictions were largely ascribed to differences in prey quality and exposure methods. In this study, we used healthy prey to expose lacewing larvae to Cry1Ab protein produced by Bt maize, and also determined the concentration of this protein at different trophic levels. Experiments were conducted in which Chrysoperla pudica (Navás) larvae were fed different diets which included aphids and healthy Bt-resistant Busseola fusca (Fuller) (Lepidoptera: Noctuidae) larvae feeding on Bt maize tissue. Lacewing larval and pupal development times as well as overall mortality were determined. The concentration of Cry1Ab protein in B. fusca larvae were fourfold reduced compared with that in leaf tissue and was below detection level in lacewing larvae. Survival to the pupal stage was higher than 96% in all treatments. Larval and pupal development periods did not differ significantly between treatments in which prey fed on Bt or non-Bt maize. This study showed feeding on healthy prey that consumed Cry1Ab protein has no adverse effect on the biology of C. pudica.

Integration of Plant Defense Traits with Biological Control of Arthropod Pests: Challenges and Opportunities

Crop plants exhibit a wide diversity of defensive traits and strategies to protect themselves from damage by herbivorous pests and disease. These defensive traits may be naturally occurring or artificially selected through crop breeding, including introduction via genetic engineering. While these traits can have obvious and direct impacts on herbivorous pests, many have profound effects on higher trophic levels, including the natural enemies of herbivores. Multi-trophic effects of host plant resistance have the potential to influence, both positively and negatively, biological control. Plant defense traits can influence both the numerical and functional responses of natural enemies; these interactions can be semiochemically, plant toxin-, plant nutrient-, and/or physically mediated. Case studies involving predators, parasitoids, and pathogens of crop pests will be presented and discussed. These diverse groups of natural enemies may respond differently to crop plant traits based on their own unique biology and the ecological niches they fill. Genetically modified crop plants that have been engineered to express transgenic products affecting herbivorous pests are an additional consideration. For the most part, transgenic plant incorporated protectant (PIP) traits are compatible with biological control due to their selective toxicity to targeted pests and relatively low non-target impacts, although transgenic crops may have indirect effects on higher trophic levels and arthropod communities mediated by lower host or prey number and/or quality. Host plant resistance and biological control are two of the key pillars of integrated pest management; their potential interactions, whether they are synergistic, complementary, or disruptive, are key in understanding and achieving sustainable and effective pest management.

The end of a myth-Bt (Cry1Ab) maize does not harm green lacewings

A concern with Bt-transgenic insect-resistant plants is their potential to harm non-target organisms. Early studies reported that Cry1Ab-producing Bt maize and purified Cry1Ab harmed larvae of the green lacewing, Chrysoperla carnea. Although these effects could not be confirmed in subsequent studies, some authors still refer to them as evidence that Bt maize harms beneficial species. We provide a comprehensive review of the studies evaluating the effects of Bt (Cry1Ab) maize on C. carnea. The evidence indicates that this important predator is not affected by Bt maize or by the produced Cry1Ab protein. We discuss how conceptual models can assist environmental risk assessments, and we emphasize the importance of robust and reproducible studies.

Acquisition of Cry1Ac protein by non-target arthropods in Bt soybean fields

Soybean tissue and arthropods were collected in Bt soybean fields in China at different times during the growing season to investigate the exposure of arthropods to the plant-produced Cry1Ac toxin and the transmission of the toxin within the food web. Samples from 52 arthropod species/taxa belonging to 42 families in 10 orders were analysed for their Cry1Ac content using enzyme-linked immunosorbent assay (ELISA). Among the 22 species/taxa for which three samples were analysed, toxin concentration was highest in the grasshopper Atractomorpha sinensis and represented about 50% of the concentration in soybean leaves. Other species/taxa did not contain detectable toxin or contained a concentration that was between 1 and 10% of that detected in leaves. These Cry1Ac-positive arthropods included a number of mesophyll-feeding Hemiptera, a cicadellid, a curculionid beetle and, among the predators, a thomisid spider and an unidentified predatory bug belonging to the Anthocoridae. Within an arthropod species/taxon, the Cry1Ac content sometimes varied between life stages (nymphs/larvae vs. adults) and sampling dates (before, during, and after flowering). Our study is the first to provide information on Cry1Ac-expression levels in soybean plants and Cry1Ac concentrations in non-target arthropods in Chinese soybean fields. The data will be useful for assessing the risk of non-target arthropod exposure to Cry1Ac in soybean.

Development of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) on pollen from Bt-transgenic and conventional maize

Maize (Zea mays) pollen is highly nutritious and can be used by predatory arthropods to supplement or replace a carnivorous diet. We demonstrate that maize pollen can be utilized by larvae of the green lacewing, Chrysoperla carnea (Neuroptera: Chrysopidae) under laboratory conditions. Complete development on maize pollen was not possible, but 25% of neonates reached the third instar. When only one instar was fed with pollen and the other two instars with eggs of Ephestia kuehniella (Lepidoptera: Pyralidae), 58–87% of the larvae reached the pupal stage. The experiments included pollen produced by nine cultivars: three genetically modified (GM) cultivars expressing the Bacillus thuringiensis proteins Cry1Ab or Cry3Bb1, their corresponding non-transformed near-isolines, and three conventional cultivars. Maize cultivars were grown in two batches in a glasshouse. Their pollen differed by up to 59% in total protein content, 25% in C:N ratio, and 14% in grain diameter, but the differences were inconsistent and depended on the batch. Lacewing performance was not affected by maize cultivar. For environmental risk assessment of GM plants, in planta studies must consider the variability among conventional cultivars, individual plants, batches, and environmental conditions when evaluating the ecological significance of differences observed between GM and near-isolines.

Bt rice producing Cry1C protein does not have direct detrimental effects on the green lacewing Chrysoperla sinica (Tjeder)

The effects of insect-resistant genetically engineered rice producing Cry1C protein derived from Bacillus thuringiensis (Bt) on Chrysoperla sinica (Tjeder) (Neuroptera: Chrysopidae) were assessed in laboratory bioassays. Survival and development of C. sinica larvae were not adversely affected when the larvae were fed a diet containing purified Cry1C protein at 200 µg/g fresh weight, representing a worst-case exposure scenario; in contrast, C. sinica larvae were adversely affected when the diet contained avidin or potassium arsenate. Life table parameters of C. sinica adults did not differ when the adults were fed with Bt or non-Bt rice pollen together with a 2-M sucrose solution. Life table parameters of C. sinica adults also did not differ when the adults were fed an artificial diet with or without purified Cry1C protein at a nominal concentration that was approximately 20 times higher than that in rice pollen; in contrast, C. sinica adults were adversely affected when the diet contained potassium arsenate. In all bioassays with lacewings, the bioactivity and stability of the Cry1C protein in the diet and Cry1C protein uptake by the lacewings were confirmed by enzyme-linked immunosorbent assay (ELISA) and by bioassays with a Cry1C-sensitive lepidopteran. These results demonstrate that neither larvae nor adults of C. sinica are sensitive to Cry1C protein at concentrations higher than those encountered in the field, demonstrating that the growing of Bt rice producing Cry1C protein is unlikely to pose a risk to C. sinica.

Tier-1 assays for assessing the toxicity of insecticidal proteins produced by genetically engineered plants to non-target arthropods

In assessing an insect-resistant genetically engineered (IRGE) crop before its commercialization, researchers normally use so-called "Tier-1 assays" as the initial step to determine the effects of the crop on non-target organisms. In these tests, the insecticidal proteins (IPs) produced by the IRGEs are added to the diets of test organisms in the laboratory. Test organisms in such assays can be directly exposed to much higher concentrations of the test IPs than they would encounter in the field. The results of Tier-1 assays are thus more conservative than those generated in studies in which the organisms are exposed to the IPs by feeding on IRGE plant tissue or in the case of predators or parasites, by feeding on invertebrate prey or hosts that have fed on IRGE plant tissue. In this report, we consider three important factors that must be considered in Tier-1 assays: (i) methods for delivery of the IP to the test organisms; (ii) the need for and selection of compounds used as positive controls; and (iii) methods for monitoring the concentration, stability and bioactivity of the IP during the assay. We also analyze the existing data from Tier-1 assays regarding the toxicity of Bt Cry proteins to non-target arthropod species. The data indicate that the widely used Bt proteins have no direct toxicity to non-target organisms.

Using resistant prey demonstrates that Bt plants producing Cry1Ac, Cry2Ab, and Cry1F have no negative effects on Geocoris punctipes and Orius insidiosus

Geocoris punctipes (Say) and Orius insidiosus (Say) are generalist predators found in a wide range of crops, including cotton (Gossypium hirsutum L.) and maize (Zea mays L.), where they provide important biological control services by feeding on an array of pests, including eggs and small larvae of caterpillars. A high percentage of cotton and maize in the United States and several other countries are transgenic cultivars that produce one or more of the insecticidal Cry proteins of Bacillus thuringiensis Berliner (Bt). Here we quantify effects of three Cry proteins on the life history of these predators over two generations when they are exposed to these Cry proteins indirectly through their prey. To eliminate the confounding prey quality effects that can be introduced by Bt-susceptible prey, we used Cry1Ac/Cry2Ab-resistant Trichoplusia ni (Hübner) and Cry1 F-resistant Spodoptera frugiperda (J.E. Smith) in a series of tri-trophic studies. Survival, development, adult mass, fecundity, and fertility were similar when predators consumed larvae feeding on Cry1Ac/Cry2Ab cotton or Cry1 F maize compared with prey feeding on isogenic or near-isogenic cotton or maize. Repeated exposure of the same initial cohort over a second generation also resulted in no differences in life-history traits when feeding on non-Bt- or Bt-fed prey. Enzyme-linked immunosorbent assay showed that predators were exposed to Bt Cry proteins from their prey and that these proteins became increasingly diluted as they moved up the food chain. Results show a clear lack of effect of three common and widespread Cry proteins on these two important predator species. The use of resistant insects to eliminate prey quality effects provides a robust and meaningful assessment of exposure and hazard.

Bt rice expressing Cry2Aa does not cause direct detrimental effects on larvae of Chrysoperla sinica

To assess the potential effects of Cry2Aa-expressing insect-resistant Bt rice on Chrysoperla sinica larvae, we conducted two tritrophic bioassays using a non-target (Laodelphax striatellus) and a target herbivore (Chilo suppressalis) as prey. None of the tested life-table parameters of C. sinica did differ when fed with L. striatellus nymphs reared on either Bt or control rice plants. Similarly, C. sinica larval survival and development were not affected when fed C. suppressalis larvae that were reared on Cry2Aa-contained artificial diet compared to those fed control diet. However, the 7-day larval weight was significantly decreased in the Bt treatment and none of the C. sinica larvae developed to the adult stage. To clarify whether the observed effects were due to the direct toxicity of Cry2Aa or prey-quality mediated, we conducted a dietary exposure assay in which the toxicity of Cry2Aa to C. sinica larvae was tested. Potassium arsenate (PA) was included as a positive control. None of the tested life-table parameters of C. sinica was adversely affected when fed Cry2Aa at 500 μg/ml sucrose solution. In contrast, C. sinica larvae were adversely affected by feeding on sucrose solution containing PA. In the feeding assays, exposure of C. sinica larvae to Cry2Aa was confirmed by ELISA. Our results demonstrate that C. sinica larvae are not sensitive to Cry2Aa at concentrations exceeding the levels that the larvae may encounter in Bt rice fields. Consequently the detrimental effects observed in the tritrophic studies using Bt rice-fed C. suppressalis as prey can be attributed to the decreased prey quality due to the sensitivity of C. suppressalis larvae to Cry2Aa.

Bt crops producing Cry1Ac, Cry2Ab and Cry1F do not harm the green lacewing, Chrysoperla rufilabris

The biological control function provided by natural enemies is regarded as a protection goal that should not be harmed by the application of any new pest management tool. Plants producing Cry proteins from the bacterium, Bacillus thuringiensis (Bt), have become a major tactic for controlling pest Lepidoptera on cotton and maize and risk assessment studies are needed to ensure they do not harm important natural enemies. However, using Cry protein susceptible hosts as prey often compromises such studies. To avoid this problem we utilized pest Lepidoptera, cabbage looper (Trichoplusia ni) and fall armyworm (Spodoptera frugiperda), that were resistant to Cry1Ac produced in Bt broccoli (T. ni), Cry1Ac/Cry2Ab produced in Bt cotton (T. ni), and Cry1F produced in Bt maize (S. frugiperda). Larvae of these species were fed Bt plants or non-Bt plants and then exposed to predaceous larvae of the green lacewing Chrysoperla rufilabris. Fitness parameters (larval survival, development time, fecundity and egg hatch) of C. rufilabris were assessed over two generations. There were no differences in any of the fitness parameters regardless if C. rufilabris consumed prey (T. ni or S. frugiperda) that had consumed Bt or non-Bt plants. Additional studies confirmed that the prey contained bioactive Cry proteins when they were consumed by the predator. These studies confirm that Cry1Ac, Cry2Ab and Cry1F do not pose a hazard to the important predator C. rufilabris. This study also demonstrates the power of using resistant hosts when assessing the risk of genetically modified plants on non-target organisms.

Using field-evolved resistance to Cry1F maize in a lepidopteran pest to demonstrate no adverse effects of Cry1F on one of its major predators

Spodoptera frugiperda (JE Smith) represents the first documented case of field-evolved resistance to a genetically engineered crop expressing an insecticidal protein from Bacillus thuringiensis (Bt). In this case it was Cry1F-expressing maize (Mycogen 2A517). The ladybird beetle, Coleomegilla maculata, is a common and abundant predator that suppresses pest populations in maize and many other cropping systems. Its larvae and adults are polyphagous, feeding on aphids, thrips, lepidopteran eggs and larvae, as well as plant tissues. Thus, C. maculata may be exposed to Bt proteins expressed in genetically engineered crops by several pathways. Using Cry1F-resistant S. frugiperda larvae as prey, we evaluated the potential impact of Cry1F-expressing maize on several fitness parameters of C. maculata over two generations. Using Cry1F resistant prey removed any potential prey-mediated effects. Duration of larval and pupal stages, adult weight and female fecundity of C. maculata were not different when they were fed resistant S. frugiperda larvae reared on either Bt or control maize leaves during both generations. ELISA and insect-sensitive bioassays showed C. maculata were exposed to bioactive Cry1F protein. The insecticidal protein had no effect on C. maculata larvae, even though larvae contained 20-32 ng of Cry1F/g by fresh weight. Over all, our results demonstrated that the Cry1F protein did not affect important fitness parameters of one of S. frugiperda's major predators and that Cry1F protein did not accumulate but was strongly diluted when transferred during trophic interactions.

Microarray analysis of global gene regulation in the Cry1Ab-resistant and Cry1Ab-susceptible strains of Diatraea saccharalis

BACKGROUND

Extensive adoption of transgenic Bt corn in recent years for stalk borer control has increased risk of resistance evolution in the target pest populations. A Bt-resistant strain of the sugarcane borer, Diatraea saccharalis, was approximately 100-fold more tolerant to Cry1Ab toxin than the susceptible counterpart. To gain a better understanding of the molecular mechanisms of Bt resistance, the Cry1Ab-susceptible (Cry1Ab-SS) and Cry1Ab-resistant (Cry1Ab-RR) strains of D. saccharalis were subjected to a microarray analysis.

RESULTS

Results showed that the expression levels of many genes were significantly different between the Cry1Ab-RR and Cry1Ab-SS strains. Microarray analysis of 7145 cDNAs revealed 384 differentially expressed genes. A total of 273 genes were significantly upregulated 2-51.6-fold, and 111 genes were significantly downregulated 2-22.6-fold in the Cry1Ab-RR strain. The upregulation of three potential resistance-related genes, coding for a glutathione S-transferase (GST), a chymotrypsin-like protease (CHY) and a lipase (LP), was confirmed using real-time PCR, indicating a reproducibility of the microarray data. Ontology analysis revealed that more than twice the number of metabolic-related genes were upregulated compared with downregulated genes with the same biological function. Up to 35.2% of the upregulated genes in the resistant strain were associated with catalytic activity, while only 9.5% of the downregulated genes were related to the same catalytic molecular function.

CONCLUSION

The large portion of metabolic- or catalytic-related genes with significant upregulations indicated a potential large increase in metabolic or catalytic activities in the Cry1Ab-RR strain. This cDNA microarray gene expression data could be used to characterize and identify new genes that may be associated with Bt resistance in D. saccharalis.

A comprehensive assessment of the effects of Bt cotton on Coleomegilla maculata demonstrates no detrimental effects by Cry1Ac and Cry2Ab

The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.

Risk assessment and ecological effects of transgenic Bacillus thuringiensis crops on non-target organisms

The application of recombinant DNA technology has resulted in many insect-resistant varieties by genetic engineering (GE). Crops expressing Cry toxins derived from Bacillus thuringiensis (Bt) have been planted worldwide, and are an effective tool for pest control. However, one ecological concern regarding the potential effects of insect-resistant GE plants on non-target organisms (NTOs) has been continually debated. In the present study, we briefly summarize the data regarding the development and commercial use of transgenic Bt varieties, elaborate on the procedure and methods for assessing the non-target effects of insect-resistant GE plants, and synthetically analyze the related research results, mostly those published between 2005 and 2010. A mass of laboratory and field studies have shown that the currently available Bt crops have no direct detrimental effects on NTOs due to their narrow spectrum of activity, and Bt crops are increasing the abundance of some beneficial insects and improving the natural control of specific pests. The use of Bt crops, such as Bt maize and Bt cotton, results in significant reductions of insecticide application and clear benefits on the environment and farmer health. Consequently, Bt crops can be a useful component of integrated pest management systems to protect the crop from targeted pests.

Effect of Bt broccoli and resistant genotype of Plutella xylostella (Lepidoptera: Plutellidae) on development and host acceptance of the parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae)

The ecological implications on biological control of insecticidal transgenic plants, which produce crystal (Cry) proteins from the soil bacterium Bacillus thuringiensis (Bt), remain a contentious issue and affect risk assessment decisions. In this study, we used a unique system of resistant insects, Bt plants and a parasitoid to critically evaluate this issue. The effects of broccoli type (normal or expressing Cry1Ac protein) and insect genotype (susceptible or Cry1Ac-resistant) of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined for their effects on the development and host foraging behavior of the parasitoid, Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) over two generations. Parasitism rate and development of D. insulare were not significantly different when different genotypes (Bt-resistant or susceptible) of insect host larvae fed on non-Bt broccoli plants. D. insulare could not discriminate between resistant and susceptible genotypes of P. xylostella, nor between Bt and normal broccoli plants with different genotypes of P. xylostella feeding on them. No D. insulare could emerge from Bt broccoli-fed susceptible and heterozygous P. xylostella larvae because these larvae were unable to survive on Bt broccoli. The parasitism rate, developmental period, pupal and adult weights of D. insulare that had developed on Bt broccoli-fed Cry1Ac-resistant P. xylostella larvae were not significantly different from those that developed on non-Bt broccoli-fed larvae. Female D. insulare emerged from Cry1Ac-resistant P. xylostella that fed on Bt plants could successfully parasitize P. xylostella larvae. The life parameters of the subsequent generation of D. insulare from P. xylostella reared on Bt broccoli were not significantly different from those from non-Bt broccoli. The Cry1Ac protein was detected in P. xylostella and in D. insulare when hosts fed on Bt broccoli. These results are the first to indicate that Cry1Ac did not harm the development or host acceptance of an important endoparasitoid after two generations of exposure. We suggest that using other Bt crops and resistant insect species would likely lead to similar conclusions about the safety of the presently used Bt proteins on parasitoids.

Recommendations for the design of laboratory studies on non-target arthropods for risk assessment of genetically engineered plants

This paper provides recommendations on experimental design for early-tier laboratory studies used in risk assessments to evaluate potential adverse impacts of arthropod-resistant genetically engineered (GE) plants on non-target arthropods (NTAs). While we rely heavily on the currently used proteins from Bacillus thuringiensis (Bt) in this discussion, the concepts apply to other arthropod-active proteins. A risk may exist if the newly acquired trait of the GE plant has adverse effects on NTAs when they are exposed to the arthropod-active protein. Typically, the risk assessment follows a tiered approach that starts with laboratory studies under worst-case exposure conditions; such studies have a high ability to detect adverse effects on non-target species. Clear guidance on how such data are produced in laboratory studies assists the product developers and risk assessors. The studies should be reproducible and test clearly defined risk hypotheses. These properties contribute to the robustness of, and confidence in, environmental risk assessments for GE plants. Data from NTA studies, collected during the analysis phase of an environmental risk assessment, are critical to the outcome of the assessment and ultimately the decision taken by regulatory authorities on the release of a GE plant. Confidence in the results of early-tier laboratory studies is a precondition for the acceptance of data across regulatory jurisdictions and should encourage agencies to share useful information and thus avoid redundant testing.