**8. Bioinsecticides based on** *Bt*

Worldwide, the use of biopesticides increases 16% annually, which represents approximately 8% of the pesticide trade in the world [12]. The formulations derived from natural materials such as bacteria, animals, plants, or minerals offer a powerful tool to create a new generation of sustainable products [84]. About 90% of microbial biopesticides are derived from a single entomopathogenic species *Bacillus thuringiensis* [85].

*Bt*-based bioinsecticides are classified into first-line products up to the fourth generation: (1) They are made up of spores and crystals, have several drawbacks, since they present a narrow range of activity when more than one pest insect is present, have little persistence in the field to solar radiation, and do not reach insects that attack roots or internal parts of the plant. (2) They contain spores and toxins of strains as an active ingredient with the introduction of genes from other


### **Table 2.**

*Varieties of Bt used as bioinsecticides, susceptible insects, expressing δ-endotoxin, and companies that produce it.*

strains, which is very useful to improve the action against the insect, generating a synergism, as well as diminishing the possibilities of resistance. (3) They contain recombinant bacteria, especially Pseudomonas fluorescens or *Clavibacter xyli* subsp. *cynodontis*, which are able to reach plant tissues and grow in the rhizosphere. (4) They constitute protein chimeras [86].

The varieties of *Bt* used commercially for the production of bioinsecticides for the control of Lepidoptera are *kurstaki* and *aizawai*, for Coleoptera the *san diego*, *tenebrionis* and *galleriae* are used, and for the control of dipteros, the *israelensis* is the most used (**Table 2**) [48, 74, 78, 87].

### **9. Applications**

More than a century after its discovery, *Bt* has become an important tool for the management of insect pests, whether in the agricultural sector or in the fight against vectors of diseases. Since then the spectrum of its applications has been increasing and is no longer limited to its initial function. It has become evident that the potential of *Bt* would transcend the biological control of insects, and recent studies analyze new properties for this old acquaintance [88].

These new environmental features include the toxicity against nematodes, mites, and ticks, antagonistic effects against plant and animal pathogenic bacteria and fungi, plant growth-promoting rhizobacteria (PGPR) activities, bioremediation of different heavy metals and other pollutants, biosynthesis of metal nanoparticles, production of polyhydroxyalkanoate biopolymer, and anticancer activities (due to parasporins) [51–53].

Toxicity against nematodes with several classes of Cry toxin (Cry5, Cry6, Cry13, Cry14, Cry21, and Cry55) is well established. In addition to these Cry proteins, thuringiensin, chitinase, and a metalloproteinase from *Bt* are also toxic to nematodes [89]. In contrast, the information about the effect of *Bt* on mites is rare, and a few in vitro and in vivo studies have reported the acaricidal activity of some *Bt* strains. In a study conducted by Dunstand et al. [90], the in vitro acaricidal activity was reported to be caused by the strain GP532 of *Bt* on the mite *Psoroptes cuniculi*. Histological alterations caused by *Bt* on this mite included the presence of dilated intercellular spaces in the basal membrane, membrane detachment of the peritrophic matrix, and morphological alterations in columnar cells of the intestine.

**197**

**Table 3.**

*Toxic Potential of Bacillus thuringiensis: An Overview DOI: http://dx.doi.org/10.5772/intechopen.85756*

solubilization enzymes, and siderophore production [92].

hemolymph of susceptible insects [93].

**10. Advantages and disadvantages**

following [34] (**Table 3**):

chemical insecticides

longer found

Cry proteins synthesized by *Bt* do not show any antifungal activity. However, some *Bt* strains produce antifungal compounds, including cell wall-degrading enzymes, lipopeptide fengycin [21]. In a study conducted by Shrestha et al. [91], *Bt* strain C25 was antagonistic to *Sclerotinia minor* and *Sclerotinia sclerotiorum*, and it was found that the strain was capable of inhibited mycelial growth, suppressed sclerotia formation, and germination. On the other hand, strain C25 showed high activities of various cell wall-degrading enzymes such as proteases, β-1,3-glucanase, and chitins. Some strains of *Bt* colonize plant roots and have plant growth-promoting characteristics. Many *Bt* strains produce some metabolites which enhance plant growth at abiotic stress conditions. These compounds include 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, indole-3-acetic acid (IAA), proline, phosphate

Different strains of *Bt* have been shown to produce many potential factors that could be of great interest in the biocontrol of phytopathogenic bacteria [55]. *Bt* produces bacteriocins, chitinases, acyl homoserine lactone lactonase, and zwittermicin, which collectively elicit detrimental effects on insect hosts and target bacteria; although the role of *Bt* bacteriocins in nature is enigmatic, it is possible that they assist in pathogenesis by attacking competing endosymbiotic or opportunistic bacteria, thereby facilitating propagation of this entomopathogen in the

Parasporins are a heterogenous group of Cry proteins produced by noninsecticidal *Bt* strains that specifically act on human cancer cells without affecting normal ones, and it has been reported that Cry proteins, such as Cry31A, Cry41A, Cry45A, Cry46A, Cry63A, and Cry64A, present anticancer activity when digested with proteases [53].

The biopesticide based on bacteria is probably the most used and is cheaper

Application with difficulty

Its quality could not be controlled. Sometimes it works, and sometimes it

Location. Its use may be limited to faunas

Variability in insect resistance

of a certain region

producers

does not

than the other methods of bioregulation of pests [94]. Almost 90% of the microbial biopesticides that are commercially available are *Bt* derivatives [95]. Among the advantages and disadvantages of using Bt as a bioinsecticide are the

**Advantages Disadvantages**

*High toxicity*: a small amount is needed to kill pests It is not easy to produce it

*Specificity*: it only kills the target organism Little diffusion and acceptance by

*Performance*: although each kilogram is more expensive, only a few grams per hectare are needed compared to 4 kg of

*It does not produce infections*: it is demonstrated that an infected larva does not harm other insects, animals, or even humans

*Few cases of resistance*: there are few cases reported, and only in extraordinary conditions there are certain degrees of resistance

*Limited time of permanence in the environment*: after 3 or 4 weeks of application, traces of the bioinsecticide are no

*Advantages and disadvantages of bioinsecticides based on Bt.*

*Toxic Potential of Bacillus thuringiensis: An Overview DOI: http://dx.doi.org/10.5772/intechopen.85756*

*Protecting Rice Grains in the Post-Genomic Era*

**insects**

*kurstaki* Lepidoptera Cry1Aa, Cry1Ab, Cry1Ac,

*aizawai* Lepidoptera Cry1Aa, Cry1Ab, Cry1Ba,

*israelensis* Diptera Cry4A, Cry4B, Cry11A,

*san diego* Coleoptera Cry3Aa Mycogen

and Cyt1Aa

*galleriae* Coleoptera Cry8Da Phyllom BioProducts

*Bt* **variety Susceptible** 

(4) They constitute protein chimeras [86].

the most used (**Table 2**) [48, 74, 78, 87].

**9. Applications**

**Table 2.**

parasporins) [51–53].

strains, which is very useful to improve the action against the insect, generating a synergism, as well as diminishing the possibilities of resistance. (3) They contain recombinant bacteria, especially Pseudomonas fluorescens or *Clavibacter xyli* subsp. *cynodontis*, which are able to reach plant tissues and grow in the rhizosphere.

*Varieties of Bt used as bioinsecticides, susceptible insects, expressing δ-endotoxin, and companies that produce it.*

Cry2Aa, and Cry2Ab

Cry1Ca, and Cry1Da

*tenebrionis* Coleoptera Cry3Aa Thermo Trilogy, Columbia MD, Certis

**δ-Endotoxin Producer company**

Abbott-Dupont and Certis

Abbott-Dupont and Kenogard

Mycogen, and Novo Nordisk

Certis

Abbott-Dupont, Novo Nordisk, and

The varieties of *Bt* used commercially for the production of bioinsecticides for the control of Lepidoptera are *kurstaki* and *aizawai*, for Coleoptera the *san diego*, *tenebrionis* and *galleriae* are used, and for the control of dipteros, the *israelensis* is

More than a century after its discovery, *Bt* has become an important tool for the management of insect pests, whether in the agricultural sector or in the fight against vectors of diseases. Since then the spectrum of its applications has been increasing and is no longer limited to its initial function. It has become evident that the potential of *Bt* would transcend the biological control of insects, and recent

These new environmental features include the toxicity against nematodes, mites,

and ticks, antagonistic effects against plant and animal pathogenic bacteria and fungi, plant growth-promoting rhizobacteria (PGPR) activities, bioremediation of different heavy metals and other pollutants, biosynthesis of metal nanoparticles, production of polyhydroxyalkanoate biopolymer, and anticancer activities (due to

Toxicity against nematodes with several classes of Cry toxin (Cry5, Cry6, Cry13, Cry14, Cry21, and Cry55) is well established. In addition to these Cry proteins, thuringiensin, chitinase, and a metalloproteinase from *Bt* are also toxic to nematodes [89]. In contrast, the information about the effect of *Bt* on mites is rare, and a few in vitro and in vivo studies have reported the acaricidal activity of some *Bt* strains. In a study conducted by Dunstand et al. [90], the in vitro acaricidal activity was reported to be caused by the strain GP532 of *Bt* on the mite *Psoroptes cuniculi*. Histological alterations caused by *Bt* on this mite included the presence of dilated intercellular spaces in the basal membrane, membrane detachment of the peritrophic matrix, and morphological alterations in columnar cells

studies analyze new properties for this old acquaintance [88].

**196**

of the intestine.

Cry proteins synthesized by *Bt* do not show any antifungal activity. However, some *Bt* strains produce antifungal compounds, including cell wall-degrading enzymes, lipopeptide fengycin [21]. In a study conducted by Shrestha et al. [91], *Bt* strain C25 was antagonistic to *Sclerotinia minor* and *Sclerotinia sclerotiorum*, and it was found that the strain was capable of inhibited mycelial growth, suppressed sclerotia formation, and germination. On the other hand, strain C25 showed high activities of various cell wall-degrading enzymes such as proteases, β-1,3-glucanase, and chitins.

Some strains of *Bt* colonize plant roots and have plant growth-promoting characteristics. Many *Bt* strains produce some metabolites which enhance plant growth at abiotic stress conditions. These compounds include 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, indole-3-acetic acid (IAA), proline, phosphate solubilization enzymes, and siderophore production [92].

Different strains of *Bt* have been shown to produce many potential factors that could be of great interest in the biocontrol of phytopathogenic bacteria [55]. *Bt* produces bacteriocins, chitinases, acyl homoserine lactone lactonase, and zwittermicin, which collectively elicit detrimental effects on insect hosts and target bacteria; although the role of *Bt* bacteriocins in nature is enigmatic, it is possible that they assist in pathogenesis by attacking competing endosymbiotic or opportunistic bacteria, thereby facilitating propagation of this entomopathogen in the hemolymph of susceptible insects [93].

Parasporins are a heterogenous group of Cry proteins produced by noninsecticidal *Bt* strains that specifically act on human cancer cells without affecting normal ones, and it has been reported that Cry proteins, such as Cry31A, Cry41A, Cry45A, Cry46A, Cry63A, and Cry64A, present anticancer activity when digested with proteases [53].

### **10. Advantages and disadvantages**

The biopesticide based on bacteria is probably the most used and is cheaper than the other methods of bioregulation of pests [94]. Almost 90% of the microbial biopesticides that are commercially available are *Bt* derivatives [95]. Among the advantages and disadvantages of using Bt as a bioinsecticide are the following [34] (**Table 3**):


### **Table 3.**

*Advantages and disadvantages of bioinsecticides based on Bt.*
