Prey‐mediated effects of Cry1Ab toxin and protoxin and Cry2A protoxin on the predator Chrysoperla carnea

Abstract

Laboratory feeding experiments were carried out to study prey-mediated effects of artificial diet containing Bacillus thuringiensis proteins on immature Chrysoperla carnea. Activated Cry1Ab toxin and the protoxins of Cry1Ab and Cry2A were mixed into standard meridic diet for Spodoptera littoralis (Boisduval) larvae at the following concentrations; for Cry1Ab toxin, 25, 50, 100 µg g −1 diet were used; for Cry1Ab protoxin, the concentration was doubled (50 µg g −1 diet, 100 µg g −1 diet and 200 µg g −1 diet) to give relative comparable levels of toxin concentration. Cry2A protoxin was incorporated into the meridic diet at one concentration only (100 µg g −1 diet). For the untreated control, the equivalent amount of double distilled water was added to the meridic diet. Individual C. carnea larvae were raised on S. littoralis larvae fed with one of the respective treated meridic diets described above. The objectives were to quantify and compare the resulting effects on mortality and development time of C. carnea with those observed in two previous studies investigating prey-mediated effects of transgenic Cry1Ab toxin-producing corn plants and the other studying effects of Cry1Ab toxin fed directly to C. carnea larvae. Mean total immature mortality for chrysopid larvae reared on B. thuringiensis-fed prey was always significantly higher than in the control (26%). Total immature mortality of C. carnea reared on Cry1Ab toxin 100 µg g −1 diet-fed prey was highest (78%) and declined with decreasing toxin concentration. Cry1Ab protoxin-exposed C. carnea larvae did not exhibit a dose response. Prey-mediated total mortality of Cry1Ab protoxin-exposed chrysopid larvae was intermediate (46-62%) to Cry1Ab toxin exposed (55-78%) and Cry2A protoxin (47%) exposed C. carnea. In agreement with the previous studies, total development time of C. carnea was not consistently, significantly affected by the Bt-treatments except at the highest Cry1Ab toxin concentration. However, both highest mortality and delayed development of immature C. carnea raised on Cry1Ab toxin 100 µg g −1 diet -fed prey may have been confounded with an increased intoxication of S. littoralis larvae that was observed at that concentration. At all other B. thuringiensis protein concentrations S. littoralis was not lethally affected. Comparative analysis of the results of this study with those of the two previous studies revealed that in addition to prey/herbivore by B. thuringiensis interactions, also prey/herbivore by plant interactions exist that contribute to the observed toxicity of B. thuringiensis -fed S. littoralis larvae for C. carnea. These findings demonstrate that tritrophic level studies are necessary to assess the long-term compatibility of insecticidal plants with important natural enemies.

Ecological compatibility of GM crops and biological control

“…Also, findings are limited to specific transformation events or cultivars of the tested GM plants rather than solely Cry toxins, and cannot be reliably extrapolated to other GM events or cultivars. Hilbeck et al (1998aHilbeck et al ( , 1999, Zwahlen et al (2000), Lundgren and Wiedenmann (2005) Duan et al (2008a), Wolfenbarger et al (2008) lowered (Rao et al, 1998;Kanrar et al, 2002), unaffected (Shieh et al, 1994), or increased Faria et al, 2007) on GM plants compared with non-GM counterparts. In one case, planthoppers that consume Bt rice avoided the phloem sap and fed more heavily on the xylem, thereby changing the nutritional content of their honeydew .…”

“…For instance, nectar production and sugar content is sometimes altered in GM crops from that observed in non-GM counterparts (Picard-Nizou et al, 1995). The quantity of honeydew produced by hemipterans may be Hilbeck et al (1998aHilbeck et al ( , 1999, Zwahlen et al (2000), Duan et al (2006Duan et al ( , 2007Duan et al ( , 2008b, Torres and Ruberson (2007), Romeis et al (2008a) Tritrophic interaction-based Detects prey-or host (hereafter referred to as prey)-mediated effects of GM crops on natural enemies, including both prey-based toxicity and prey quality. In these studies, prey are fed GM plant tissues or diets containing the transgenederived products (e.g., insecticidal Bt Cry proteins).…”

Ecological Impacts of Genetically Modified Crops: Ten Years of Field Research and Commercial Cultivation

“…Adverse effects on mortality, longevity or development of predators were only reported in studies using Bt-susceptible lepidopteran larvae as prey that had ingested the Bt-toxin. In particular, the green lacewing (Chrysoperla carnea), an important predator in many maize growing areas, has thoroughly been studied since studies suggested that this predator was negatively affected by Cry1Ab [31][32][33]. Results of subsequent studies using several different prey species reared on Cry1Ab-maize, however, showed that the insecticidal protein itself does not directly affect this predator, but that the green lacewing may be affected when feeding on prey species that are susceptible to Bttoxin [34][35][36].…”

The release of genetically modified crops into the environment

“…Although Hilbeck et al, (1999) suggest that the transgenic expression of Bt toxin gene in maize may have altered the specificity of the toxin, there are no convincing data to support such a suggestion. The prey used was Spodoptera littoralis, whereas in field situations lacewing larvae tend to prefer aphids as prey.…”