Potential impact of host pest fed on Bt-modified corn on the development of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae)
© The Author(s) 2018
Received: 18 June 2017
Accepted: 6 December 2017
Published: 15 March 2018
Laboratory experiments were conducted to study the potential impact of genetically modified corn hybrid, transgenic Bacillus thuringiensis (Bt)-expressing (Cry2Ab/1Ac), and the corresponding isogenic untransformed Bt-free hybrid on biological parameters of the green lacewing predator, Chrysoperla carnea (Stephens). The effectiveness of transgenic (Bt)-expressing (Cry2Ab/1Ac) on C. carnea developmental parameters (larval duration, pupal duration, mortality %, pupation %, adult emergence %, and adult duration time) was investigated in the first experiment. In the second experiment, the effect of Bt Cry2Ab and Cry1Ac partially purified toxins on the hatchability of C. carnea eggs compared to cypermethrin was examined. Additionally, the toxicity effect of Angoumois grain moth, Sitotroga cerealella, eggs sprayed with BtCry2Ab/1Ac mixture and cypermethrin on C. carnea was tested. The results showed that the mortality percentage of C. carnea fed on aphids reared on Bt corn (40%) was less than that fed on aphids reared on non-Bt corn (50%). Moreover, the larval mortality %, net pupation, and adults’ emergence percentage of C. carnea larvae fed on aphids reared on Bt corn and non-Bt corn were not significantly different. On the other hand, the hatchability data showed that the chemical insecticide (cypermethrin) severely affected the C. carnea eggs compared to Cry2Ab/1Ac toxins. These findings proved that adopting biopesticide formulation based on Bt toxins or Bt-modified crops will not only affect C. carnea but also enhance its ability as a potential biological pest control agent.
Different Bacillus thuringiensis (Bt) have been used widely to control lepidopterans, dipterans, and coleopterans insect pests over the last five decades. Among the environmentally friendly pesticides, B. thuringiensis-based products alone account for 90–92% of the 1% market share of biopesticides in the total pesticide market. Generally, B. thuringiensis endotoxins are considered as safe biopesticides to vertebrates and beneficial arthropods and are often highly toxic to insect pests. Genes encoding Bt toxins were among the first to be used in genetic engineering of plants to overcome insect resistance.
Since 1996, plants have been modified with short sequences of genes from Bt to express the crystal protein. In this technology, plants themselves can produce the proteins and protect themselves from insect damage. The use of genetic engineering techniques to transfer desired traits in insect, disease, and weed control has provided farmers with new tools to control some stubborn problems (James, 2004). Some of the first genetically engineered crops have been modified to express insecticidal crystalline (Cry) proteins derived from the common soil bacterium B. thuringiensis (Bt) Berliner (Perlak et al., 1991). These so-called Bt crops are protected from the feeding of various groups of insect pests. They provide pest control solutions that are highly effective and yet very specific, leading to substantial direct benefits for farmers as well as providing greater flexibility in crop management practices. Among them, Bt corn is considered as an ideal crop system for comparing possible non-target effects of transgenic (Bt) and conventional insecticide control. This crop is heavily treated with insecticides for lepidopteran pests and has a shorter crop cycle than other transgenic crops. Thus, there is a great chance of ecological disruption, at least from insecticides, and less time for non-target populations to recover from these disturbances before the end of the crop cycle (Rose and Dively, 2007). Like any insect control technology, transgenic plant may present a risk to the natural enemy community, due to indirect contact with Cry protein by feeding on intoxicated organisms, or changes in plant chemical. On the contrary, reductions in insecticide use resulting from planting Bt corn should be beneficial to natural enemies (Betz et al., 2000). Endotoxins from Bt produced in transgenic Bt crops are generally not toxic to predatory and parasitic arthropods (Schoenly et al., 2003).
Green corn leaf aphid (GCLA), Rhopalosiphum maidis (Fitch), is a major pest of corn in Egypt, Middle East, and elsewhere; heavy infestations cause yield loss by more than 35% (Al-Eryan and El-Tabbakh, 2004). It is also considered as a major pest of sorghum, barley, sugar cane, millet, wheat, and banana in various parts of the world. This pest is attacked by various predators of different families, viz., Chrysopidae, Syrphidae, and Coccinellidae. Green lacewing, Crysoperla carnea (Stephens) (Chrysopidae), is the most effective biological control agent of aphid species. The larva of C. carnea has relatively a wide range of prey acceptance (Preetha et al., 2009), which includes aphids, whiteflies, eggs of moths, and other soft-bodied insects. As a result of the polyphagous ability and voracious nature of C. carnea in addition to its vast geographical distribution (New, 1975), there is easiness of mass multiplication (Araujo and Bichao, 1990) and tolerance to several pesticides (Hassan et al., 1985). C. carnea has received numerous attentions from farmers as well as researchers as a potential biological pest control agent. The effectiveness of C. carnea as a biological control agent has been demonstrated in field and greenhouses and reported to give about 100% lepidoptran pest control when used along with Trichogramma spp. (Hagley and Miles, 1987; Rincon, 1999). Therefore, the current study aims to investigate the potential impact of Bt transgenic plants on green lacewing predator, C. carnea.
Materials and methods
Rearing of Sitotroga cerealella (Olivier)
The eggs of Angoumois grain moth, S. cerealella (Olivier), were used as a natural food source for mass production of the green lacewing, C. carnea. In order to maintain S. cerealella pest under laboratory condition, its mother colony was kindly provided by the Stored Grain Department at the Plant Protection Research Institute. To obtain a mass production of S. cerealella eggs, the insect culture was maintained according to the method described by Hassan (1995) with some modifications where a bulk of soft wheat grains were brought to the laboratory and were sterilized at 120 °C for 2 h. About 2–3 kg of sterilized wheat grains was poured into sterilized and clean metal trays (70 × 50 cm size). These trays were kept horizontally on the bench and infested with 1 g of S. cerealella eggs/kg of wheat grains in each tray and immediately transferred into large cages for 10–12 days. The trays were then taken and kept vertically in ovipositor cages for 25–30 days till adult emergency and egg production. The deposited S. cerealella eggs were collected in small jars in 2-day intervals and were sieved in order to remove all the insect scales.
Rearing of predator, C. carnea
The starter culture of the green lacewing, C. carnea, was established by collecting the adult stage from cotton field, insecticide-free and transferred immediately to the laboratory. This culture was maintained under lab condition for several generations before starting the experiments. The adults of C. carnea were taken from original culture and were mated in plastic boxes. A number of ten pairs of adults were placed in plastic boxes (22 × 13 × 10 cm) and were covered with black muslin cloth for egg laying. A semi-artificial diet solution was prepared according to Morrison (1985). The adults were provided with droplets of mixed yeast and sugar on muslin cloth. The deposited eggs were collected daily and kept in glass jars until hatching. The hatched larvae were reared on S. cerealella eggs as mentioned above.
Rearing of the aphid, Rhopalosiphum maidis (Fitch)
In order to obtain enough culture of aphid that fed for several generations on Bt corn plants, a number of 20–30 individuals of R. maidis were released on Bt corn which contained a synthetic Cry2Ab/1Ac gene encoding a nearly full length Cry2Ab protein. Both transgenic and non-transgenic corn plants were sown and grown in the greenhouses. Three months after cultivation, the nymphs of GCLA were collected from the infested corn leaves for predator feeding assay.
Predator feeding assay
Feeding effect of aphid reared on Bt transgenic lines on the development of C. carnea
In order to study the influence of feeding C. carnea on hosts that fed on transgenic line, the infested leaves with R. maidis individuals of Bt corn and non-Bt corn greenhouses were collected and transferred to the lab for predator assay. Twenty individuals of the second instar larvae of C. carnea were kept individually in culture tubes; each tube was considered as one replicate. Fifty aphids were collected from the infested corn leaves then introduced to each larva daily till pupation. Daily observations were performed till adult stage. In each assay, the larval duration of the C. carnea, larval mortality percentage, pupation percentage, pupal duration, percentage of the emerged adult, percentage of assayed larvae survived till adult emergence and the number of aphid individuals eaten by each larva were recorded.
Bacillus thuringiensis Cry1Ac and Cry2Ab toxin preparation
BtCry1Ac and Cry2Ab effects on egg hatchability of C. carnea
Feeding effect of S. cerealella eggs sprayed with BtCry1Ac/2Ab toxins on C. carnea
To determine the feeding effect of S. cerealella eggs treated with Bt Cry1Ac and Cry2Ab toxins on green lacewing predator compared to the effect feeding of GCLA reared on Bt corn, the partially purified BtCry1Ac and BtCry2Ab toxins were sprayed on eggs of S. cerealella pest at various concentrations which ranged from 4 to 10 μg toxin/ml dH2O. Similarly, the negative and positive control treatments were also deliberated, but Bt toxins in this experiment were replaced with dH2O (as a negative control) and cypermethrin compound (as a positive control). In each concentration, three replicates of 20 green lacewings on the first day of the second larval instar were released on the treated eggs with a fine brush and then kept at the abovementioned laboratory condition for 4 days and examined 4 days after treatment. The experiments were repeated several times in order to obtain accurate data. The experiments were accomplished at 26 ± 1 °C and 65–70% RH.
One-way analysis of variance (ANOVA) was applied by the Duncan multiple range test for comparison of means at P < 0.05, Student’s t test, and depletion rates, which were computerized according to IBM-SPSS, 2011). Additionally, Abbott’s formula (Abbott, 1925) was implemented to correct the larval mortality percentage.
Results and discussion
Development of C. carnea fed on aphids reared on Bt corn
Effect of aphids fed on Bt and non-Bt corn on the development of the immature stages of, C. carnea
Bt corn line
Non-Bt corn line
Mean number of aphids consumed by each larva
222.5 ± 7.28
253.5 ± 6.65*
Larval duration (mean/day)
9.0 ± 0.11
9.9 ± 0.17*
Pupal duration (mean/day)
10.4 ± 0.07
10 ± 0.08*
Pupation (completed) %
Adult emergence %
Percentage of assayed larvae survived till adult emergence
Comparison between the effect of Cry1Ac and Cry2Ab toxins on egg hatchability of C. carnea
Effect of Bt Cry1Ac and Cry2Ab toxins on egg hatchability of C. carnea
Cry 1Ab (μg/ml)
Cypermetherin (2 μg/ul)
Mean no. of hatched C. carnea eggs
19.0 ± 1.13a
18.33 ± 1.13a
18.0 ± 1.13a
19.33 ± 1.13a
18.33 ± 1.13a
17.33 ± 1.13a
16.66 ± 1.13a
On the other hand, the hatchability of C. carnea eggs treated with cypermetherin (positive control) was nil and the difference between the positive control and all other treatments was significant. Tian et al. (2013) confirmed that Cry1Ac and Cry2Ab did not affect the egg hatchability of C. rufilabris.
Effect of Bt toxins on C. carnea
Effect of S. cerealella eggs sprayed with cypermethrin and the mixture of Cry1Ac and Cry 2Ab on the larval mortality of C. carnea
Mean no. of mortality
% Corrected mortality
Cry1Ac + Cry 2Ab
Additionally, Dutton et al. (2002) and Obrist et al. (2006) did not find any direct effect for Cry1A protein class on lacewing larvae. Considering that the green lacewing is a generalist predator which, in addition to feeding on lepidopteran larvae and mites, also feeds on aphids and other insect eggs in the field, it is highly unlikely that Bt crops pose any risk to this beneficial predator.
The overall conclusion of the current study is that Bt corn lines has no direct or indirect effect on C. carnea. A respectable number of developed and developing countries adopted transgenic crops two decades ago. But, several concerns still stand as obstacles to accept this technology by public. Effect of modified crops on the biological activity of the predation level of insect predators such as C. carnea is assumed to be a major problem. Therefore, the current study proved that the biological activity of C. carnea will not be affected by adopting Bt corn. This finding may also help the Egyptian Government to reconsider the adoption of Bt-modified crops plan for reclamation of 4 million feddan of the desert land in the coming years.
The authors thank the Plant Protection Research Institute and the Agriculture Research Center for facilitating the work during the study. We are gratefully acknowledged the Science and Technology Development Fund (STDF) for funding this work through the project number 4653. Also, we would like to thank the board of STDF organization for their support and encourages throughout the research.
SM has planed the outline of the research work, did the bioassay experiments and drafted the manuscript. FB carried out the data analysis and helped in cultivating the Bt corn. KA was responsible for rearing the C carnea predator and S. cerealella cultures. MN anticipated in collection the aphids individuals and preparing Bt toxins. EM carried out insect assay and data observations. EAK anticipated in insect collection and Bt toxin purification along with revising the draft of the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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