Use of Bacillus thuringiensis toxins for control of the cotton pest Earias insulana (Boisd.) (Lepidoptera: Noctuidae)

Engineered chimeric insecticidal crystalline protein improves resistance to lepidopteran insects in rice (Oryza sativa L.) and maize (Zea mays L.)

The insecticidal crystalline proteins (Crys) are a family of insect endotoxin functioning in crop protection. As insects keep evolving into tolerance to the existing Crys, it is necessary to discover new Cry proteins to overcome potential threatens. Crys possess three functional domains at their N-termini, and the most active region throughout evolution was found at the domain-III. We swapped domain-IIIs from various Cry proteins and generated seven chimeric proteins. All recombinants were expressed in Escherichia coli and their toxicity was assessed by dietary exposure assays. Three of the seven Crys exhibited a high toxicity to Asian corn borer over the controls. One of them, Cry1Ab-Gc, a chimeric Cry1Ab being replaced with the domain-III of Cry1Gc, showed the highest toxicity to rice stem borer when it was over-expressed in Oryza sativa. Furthermore, it was also transformed into maize, backcrossed into commercial maize inbred lines and then produced hybrid to evaluate their commercial value. Transgenic maize performed significant resistance to the Asian corn borer without affecting the yield. We further showed that this new protein did not have adverse effects on the environment. Our results indicated that domain III swapped of Crys could be used as an efficient method for developing new engineered insecticidal protein.

Whole Genome Sequencing Analysis of Bacillus thuringiensis GR007 Reveals Multiple Pesticidal Protein Genes

Bacillus thuringiensis (Bt) are soil ubiquitous bacteria. They produce a great variability of insecticidal proteins, where certain of these toxins are used worldwide for pest control. Through their adaptation to diverse ecosystems, certain Bt strains have acquired genetic mobile elements by horizontal transfer, harboring genes that encode for different virulent factors and pesticidal proteins (PP). Genomic characterization of Bt strains provides a valuable source of PP with potential biotechnological applications for pest control. In this work, we have sequenced the complete genome of the bacterium Bt GR007 strain that is toxic to Spodoptera frugiperda and Manduca sexta larvae. Four replicons (one circular chromosome and three megaplasmids) were identified. The two largest megaplasmids (pGR340 and pGR157) contain multiple genes that codify for pesticidal proteins: 10 cry genes (cry1Ab, cry1Bb, cry1Da, cry1Fb, cry1Hb, cry1Id, cry1Ja, cry1Ka, cry1Nb, and cry2Ad), two vip genes (vip3Af and vip3Ag), two binary toxin genes (vpa2Ac and vpb1Ca), five genes that codify for insecticidal toxin components (Tc’s), and a truncated cry1Bd-like gene. In addition, genes that codify for several virulent factors were also found in this strain. Proteomic analysis of the parasporal crystals of GR007 revealed that they are composed of eight Cry proteins. Further cloning of these genes for their individual expression in Bt acrystalliferous strain, by means of their own intrinsic promoter showed expression of seven Cry proteins. These proteins display differential toxicity against M. sexta and S. frugiperda larvae, where Cry1Bb showed to be the most active protein against S. frugiperda larvae and Cry1Ka the most active protein against M. sexta larvae.

Field Evolved Resistance in Earias vittella (Lepidoptera: Noctuidae) From Punjab, Pakistan Against Commercial Formulations of Bacillus thuringiensis kurstaki

Transgenic commercial cotton expressing Bacillus thuringiensis (Bt) Cry endotoxins or vegetative Vip toxins provide protection to cotton against bollworm attack. Continuous exposure of these targeted pests to cry toxins and to Bt commercial spray formulations has resulted in the development of resistance through natural selection. Spotted bollworm Earias vittella (Noctuidae: Lepidoptera) is considered to be one of the most destructive pests of cotton and okra crops in South Asia including Pakistan and has developed resistance to various synthetic insecticides. In the present study, the level of resistance in field populations of the spotted bollworm E. vittella against Bt Cry toxins has been evaluated for the first time. We collected twelve populations of E. vittella from three districts of Punjab, Pakistan for testing against four commercial Bt formulations containing different strains of B. thuringiensis subspecies kurstaki (Btk) with a range of Cry toxins. Low to high levels of resistance were found in the field populations compared with a laboratory-reared susceptible population of E. vittella (resistance ratios 6 to 111-fold). These results suggest that E. vittella has developed resistance against different Cry toxins after continuous exposure to Bt cotton in field. In order to prevent field control failures, regular insecticide resistance monitoring programs are required together with the use of integrated management approaches, including the use of Bt cotton varieties expressing two or more toxins to delay the development of resistance against Bt toxins in E. vittella.

Fitness Costs of Two Maize Lepidopteran Pests Fed on Bacillus thuringiensis (Bt) Diets Enriched with Vitamins A and C

Simple Summary

Biotechnologists are designing new transgenic plants enriched with micronutrients and vitamins that are resistant to insects. These new plants could favor the development of some pest insects. This work aims to discover the effect of adding two vitamins, A and C, to insect diets prepared with Bt and no-Bt maize in two maize insect pests. M. unipuncta was less sensitive to the toxin, although ingestion of the Bt diet resulted in longer larval development and lower pupal weight, which were not mitigated by any of the vitamins. However, the two vitamins reduced the mortality of H. armigera larvae fed on the Bt diet. In addition, we found evidence of the antioxidant function of vitamin A. The results obtained here indicate that crops enriched with these vitamins will hardly favor the development of H. armigera and suggest that they do not affect M. unipuncta’s development at all.

Abstract

Serious malnutrition problems occur in developing countries where people’s diets are mainly based on staple crops. To alleviate this, high-production crops are being developed that are better adapted to climate change, enriched in micronutrients and vitamins, or resistant to pests. In some cases, new varieties have been developed with several of the characteristics mentioned above, such as biofortified and pest-resistant crops. The development of biofortified Bacillus thuringiensis (Bt) crops raises the question of whether vitamin enrichment of Bt crops can in any way favor those pests that are not very susceptible to the Bt toxin that feed on these crops, such as Helicoverpa armigera (Hübner) or Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae). In this study, the response to a Bt diet enriched with vitamins A (β-carotene) and C (ascorbic acid) was somewhat different between the two species. M. unipuncta was less sensitive to the toxin than H. armigera, although the ingestion of the Bt diet resulted in oxidative stress (longer larval development and lower pupal weight) which was not mitigated by the vitamins. However, the two vitamins reduced the mortality of H. armigera larvae fed on a Bt-enriched diet; in addition, ß-carotene reduced the activity of the antioxidant glutathione S-transferase (GST) of both species, suggesting it has an antioxidant role. The results obtained here indicate that biofortified Bt crops will not favor the development of H. armigera very much and will not affect M. unipuncta’s development at all, although the effect of the increase in vitamins may be very variable and should be studied for each specific phytophagous.

Molecular and insecticidal characterization of a novel Cry-related protein from Bacillus thuringiensis toxic against Myzus persicae

This study describes the insecticidal activity of a novel Bacillus thuringiensis Cry-related protein with a deduced 799 amino acid sequence (~89 kDa) and ~19% pairwise identity to the 95-kDa-aphidicidal protein (sequence number 204) from patent US 8318900 and ~40% pairwise identity to the cancer cell killing Cry proteins (parasporins Cry41Ab1 and Cry41Aa1), respectively. This novel Cry-related protein contained the five conserved amino acid blocks and the three conserved domains commonly found in 3-domain Cry proteins. The protein exhibited toxic activity against the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae) with the lowest mean lethal concentration (LC₅₀ = 32.7 μg/mL) reported to date for a given Cry protein and this insect species, whereas it had no lethal toxicity against the Lepidoptera of the family Noctuidae Helicoverpa armigera (Hübner), Mamestra brassicae (L.), Spodoptera exigua (Hübner), S. frugiperda (J.E. Smith) and S. littoralis (Boisduval), at concentrations as high as ~3.5 μg/cm². This novel Cry-related protein may become a promising environmentally friendly tool for the biological control of M. persicae and possibly also for other sap sucking insect pests.

Low susceptibility of non-target Lepidopteran maize pests to the Bt protein Cry1Ab

Transgenic Bt maize expressing the Cry1Ab toxin is poorly effective for suppressing populations of two non-target Lepidoptera, Mythimna unipuncta and Helicoverpa armigera. In order to determine the mechanisms that may be involved in this poor effectiveness, last instar larvae of the two Lepidoptera were fed with a diet containing lyophilized leaves with Bt vs non-Bt toxin for different periods; additionally, some larvae fed on Bt diet were transferred to non-Bt diet for an additional period. In the experimental larvae, we measured the growth (weight) gain from just before treatment to after the end of the treatment, and the Cry1Ab contents in the hemolymph, the peritrophic membrane and its contents and midgut epithelium. Effects of the treatments on the midgut epithelium were observed by light and transmission electron microscopy. It was seen that multiple mechanisms can be involved in the low susceptibility of the two Lepidoptera. The low content of the toxin within the peritrophic membrane 48 h after ingestion indicates a high rate of toxin elimination in this space. Moreover, M. unipuncta larvae fed on the Bt diet displayed a similar growth gain index to those fed on the non-Bt diet, and showed an increasing elimination rate during the experiment. Little toxin reached the midgut epithelium, indicating a low permeability of the peritrophic membrane or a low affinity at the binding sites. Larvae fed on the Bt toxin showed rapid recovery in weight gain and in the midgut epithelium, and also showed overcompensation mechanisms.

MICROBIAL PEST CONTROL: A MATHEMATICAL MODEL

The traditional method for controlling pests is the application of chemical pesticides. Growing concern on the negative effects of chemicals has encouraged the development of alternatives. Inundatively and inoculatively applied microbial control agents (virus, bacteria, fungi, and entomopathogenic nematodes) have been developed as alternative control methods of a wide variety of pests. A mathematical model for microbial control of pests is formulated in this paper. The dynamical characteristics of the system are studied. The role of time-delay has been discussed. Numerical simulations are carried out to illustrate the analytical findings. Biological implications have been discussed.

Comparative effect of integrated pest management and farmers' standard pest control practice for managing insect pests on cabbage (Brassica spp.)

BACKGROUND

Studies were conducted on experimental cabbage plantings in 2009 and on experimental and commercial plantings in 2010, comparing farmers' current chemical standard pesticide practices with an integrated pest management (IPM) program based on the use of neem (Aza-Direct) and DiPel (Bacillus thuringiensis). In experimental plantings, the IPM program used six or eight applications of neem and DiPel on a rotational basis. The standard-practice treatments consisted of six or eight applications of carbaryl and malathion or control treatment.

RESULTS

The IPM treatments reduced pest populations and damage, resulting in a better yield than with the standard chemical or control treatment. When IPM treatment included three applications of neem plus three applications of DiPel (on a rotational basis in experimental fields), it again reduced the pest population and damage and produced a better yield than the standard practice. The lower input costs of the IPM program resulted in better economic returns in both trials.

CONCLUSIONS

The IPM components neem and DiPel are suitable for use in an IPM program for managing insect pests on cabbage (Brassica spp.).

The impact of the EU regulatory constraint of transgenic crops on farm income

World population and the need for nutritious food continue to grow. For 14 years farmers from a range of countries across the globe have been accessing transgenic technologies either to reduce crop production costs, increase yield and/or to exploit a range of rotational benefits. In 2009 134 Mha of transgenic crops was grown. The arable area of the EU 27 is approximately 102 Mha; however, only about 0.1 Mha of transgenic crops, mainly maize in Spain, is grown in the EU. This is in part due to limited approvals before the establishment of a moratorium on the cultivation of transgenic crops. In this paper we estimate the revenue foregone by EU farmers, based on the potential hectarages of IR and HT transgenic crops that have been economically successful elsewhere if they were to be grown in areas of the EU where farmers could expect an overall financial benefit. This benefit would accrue primarily from reduced input costs. We estimate that if the areas of transgenic maize, cotton, soya, oil seed rape and sugar beet were to be grown where there is agronomic need or benefit then farmer margins would increase by between €443 and €929 M/year. It is noted that this margin of revenue foregone is likely to increase if the current level of approval and growth remains low, as new transgenic events come to market and are rapidly taken up by farmers in other parts of the world.

Histopathology and ultrastructure of midgut of Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) fed Bt-cotton

The interaction of Cry toxins from Bacillus thuringiensis in the midgut of some insect larvae determines their efficacies as insecticides, due to the expression and availability of sites of action of the toxin in the midgut. Researches point out cases of resistance to Cry toxin due to alterations in the binding sites in columnar cell membrane. We analyzed the effects of Cry1Ac toxin expressed by Bt-cotton plants on Alabama argillacea midgut morphophysiology clarifying in levels of morphological and ultrastructural. Larvae in the 4th instar of A. argillacea after 20 min from ingesting Bt-cotton leaves expressing 0.183 ng of Cry1Ac exhibited ultrastructural and morphological modifications in the columnar cells with significant changes in the mitochondrial polymorphism, cytoplasmic vacuolization, microvillus and basal labyrinth. Expressive morphological alterations were also observed in the goblet cells indicating that the columnar cells are not the only target of the Cry1Ac toxin. The regenerative cells did not modify their structures and exhibited decrease in regeneration capacity. In conclusion, the ingestion of 0.183 ± 0.077 ng of Cry1Ac was enough to promote alterations in the columnar and goblet cells, besides reducing significantly the number of regenerative cells, which may have contributed to larval death. Nevertheless, further studies are necessary to determine the true cause of death.

High expression of transgene protein in Spirodela

The monocot family Lemnaceae (duckweed) is composed of small, edible, aquatic plants. Spirodela oligorrhiza SP is a duckweed with a biomass doubling time of about 2 days under controlled, axenic conditions. Stably transformed Spirodela plants were obtained following co-cultivation of regenerative calli with Agrobacterium tumefaciens. GFP activity was successfully monitored in different subcellular compartments of the plant and correlated with different targeting sequences. Transgenic lines were followed for a period of at least 18 months and more than 180 vegetative doublings (generations). The lines are stable in morphology, growth rate, transgene expression, and activity as measured by DNA-DNA and immunoblot hybridizations, fluorescence activity measurements, and antibiotic resistance. The level of transgene expression is a function of leader sequences rather than transgene copy number. A stable, transgenic, GFP expression level >25% of total soluble protein is demonstrated for the S. oligorrhiza system, making it among the higher expressing systems for nuclear transformation in a higher plant.

Potential of the Bacillus thuringiensis toxin reservoir for the control of Lobesia botrana (Lepidoptera: Tortricidae), a major pest of grape plants

The potential of Bacillus thuringiensis Cry proteins to control the grape pest Lobesia botrana was explored by testing first-instar larvae with Cry proteins belonging to the Cry1, Cry2, and Cry9 groups selected for their documented activities against Lepidoptera. Cry9Ca, a toxin from B. thuringiensis, was the protein most toxic to L. botrana larvae, followed in decreasing order by Cry2Ab, Cry1Ab, Cry2Aa, and Cry1Ia7, with 50% lethal concentration values of 0.09, 0.1, 1.4, 3.2, and 8.5 microg/ml of diet, respectively. In contrast, Cry1Fa and Cry1JA were not active at the assayed concentration (100 microg/ml). In vitro binding and competition experiments showed that none of the toxins tested (Cry1Ia, Cry2Aa, Cry2Ab, and Cry9C) shared binding sites with Cry1Ab. We conclude that either Cry1Ia or Cry9C could be used in combination with Cry1Ab to control this pest, either as the active components of B. thuringiensis sprays or expressed together in transgenic plants.

Molecular and insecticidal characterization of a Cry1I protein toxic to insects of the families Noctuidae, Tortricidae, Plutellidae, and Chrysomelidae

The most notable characteristic of Bacillus thuringiensis is its ability to produce insecticidal proteins. More than 300 different proteins have been described with specific activity against insect species. We report the molecular and insecticidal characterization of a novel cry gene encoding a protein of the Cry1I group with toxic activity towards insects of the families Noctuidae, Tortricidae, Plutellidae, and Chrysomelidae. PCR analysis detected a DNA sequence with an open reading frame of 2.2 kb which encodes a protein with a molecular mass of 80.9 kDa. Trypsin digestion of this protein resulted in a fragment of ca. 60 kDa, typical of activated Cry1 proteins. The deduced sequence of the protein has homologies of 96.1% with Cry1Ia1, 92.8% with Cry1Ib1, and 89.6% with Cry1Ic1. According to the Cry protein classification criteria, this protein was named Cry1Ia7. The expression of the gene in Escherichia coli resulted in a protein that was water soluble and toxic to several insect species. The 50% lethal concentrations for larvae of Earias insulana, Lobesia botrana, Plutella xylostella, and Leptinotarsa decemlineata were 21.1, 8.6, 12.3, and 10.0 microg/ml, respectively. Binding assays with biotinylated toxins to E. insulana and L. botrana midgut membrane vesicles revealed that Cry1Ia7 does not share binding sites with Cry1Ab or Cry1Ac proteins, which are commonly present in B. thuringiensis-treated crops and commercial B. thuringiensis-based bioinsecticides. We discuss the potential of Cry1Ia7 as an active ingredient which can be used in combination with Cry1Ab or Cry1Ac in pest control and the management of resistance to B. thuringiensis toxins.