Bacterial Insectisidesshort notes

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Commercial Bacterial bioinsecticides:

What are pests and what is the need to control them?

Pests are defined as ‘any species, strain or biotype of plant, animal or microorganism

detrimental to plants, plant products, humans, animal or environment (FA/WHO, 2014). They

can be an insect, fungi, weed, rodent, bacteria, virus, nematodes, mite, parasite, animal or bird.

These organisms diminish the value of plant resources directly or indirectly during their attempt

to secure food and can infect root, stem, leaves, flowers, fruits, buds etc (Atwal and Dhaliwal,

2015). They can also cause harm to finished farm products getting ready for sale. Crop losses

due to pest may account for about the food required to feed over 1 billion people (Birch et al,

2011). Pest control is thus an imperative step to reduce pest below a threshold to control yield

losses and increase productivity.

What are pesticides and what are their disadvantages?

The widely used method to control pests of agricultural products are chemicals called pesticides

of organic or synthetic nature like organochlorines, organophosphorus, carbamates, pyrethroids,

amides, anilins, azotic heterocyclic compounds etc (Zhang, 2007; Tano,2011). Pesticides is thus

a broad term to cover insecticides, fungicides, herbicides, rodenticides, etc to kill pests during

production, storage and processing of food and feeds. Increased demand of food resources to

feed the growing population has escalated the use of pesticides in both developed and developing

countries during the last few decades (Antonini and Argilés-Bosch, 2017; Crist et al., 2017).

Excessive use of pesticides application leaves residues of these persistent chemicals in the

environment leading to pollution and adverse human health effects (Damalas and

Eleftherohorinos, 2011; Debnath and Khan, 2017 ). Their continuous usage has also resulted in

the emergence of resistance among the target pest. They are also reported to be associated with

public health problems like dermatological, gastrointestinal, neurological, carcinogenic,

respiratory, reproductive, endocrine effects, accidental or intentional exposure even resulting in

hospitalization and death ((Kogan, 1998; Mostafalou and Abdollahi, 2013; Nicolopoulou-

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Stamati et al., 2016). Pesticides residues have also been reported in prepared meals, processed

foods, grains, milk, vegetables etc (Mariyono, 2008; Damalas and Eleftherohorinos, 2011).

What are biopesticides?

Public awareness about the deterimental effects of pesticides on food safety and environment has

triggered the concept of using eco friendly compatible approaches to support sustainable

development and pest management. Biological agents like bacteria, viruses, insects, nematodes,

botanical agents etc are gaining importance as alternatives to chemical pesticides and are a major

component of many pest control programs (Copping and Menn, 2000). The pesticides developed

from living organism like animals, plants, microorganisms etc. which can control insect pests by

their nontoxic eco friendly mode of action is called biopesticides (Mazid et al., 2011).

Biopesticides being biological in origin control pest through various mechanisms like inhibiting

growth, nutrition, development and reproduction of pest. They are emerging as a sustainable

alternative to organic farming because they are non toxic, ecofriendly, designed to target the

specific pest, reduced resistance development in pest etc (EPA, 2006). The global biopesticides

market is anticipated to grow significantly over the coming years. The global market of

biopesticides is reported to increase by 10% every year on a global scale (Marrone, 2014). It is

expected that biopesticides will compete with chemical pesticides in terms of market size,

between the late 2040s and the early 2050s (Olson, 2015; Damalas and Koutroubas, 2018).

What are Microbial biopesticides?

Microorganisms like bacteria, fungi, virus, nematodes etc. are reported to be used as microbial

biopesticides (EPA, 2006). They belong to the largest group of broad spectrum biopesticides

which are specific towards pest and contribute about 90% of the total biopesticide market.

Approximately 73 microbial agents have been registered by US EPA for microbial biopesticide

production. Among the microbial biopesticides bacteria and its products dominate the market

with about 74% share in biopesticide market (Thakore, 2006; Steinwand, 2008).

They are employed as insecticides to target specific or individual species of moths, butterflies,

beetles, flies and mosquitoes etc. Its mode of action is either by close contact with pest or by

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ingestion and varies from insect to insect. Bacteria belonging to the family Bacillaceae,

Pseudomonadaceae, Enterobacteriaceae, Streptococcaceae and Micrococcaceae are reportedly

used as bacterial pesticides. They are either spore formers (Bacillus thuringiensis), obligate,

facultative or potential pathogens (Bacillus species, Pseudomonas aeruginosa, Serratia

marcesens). These organisms produce metabolites which suppress the growth of pest by

producing toxic metabolites specific to the pest (Clemson, 2007). Extended research and

expanded technologies on microorganisms have led to the discovery, development, and market

launch of several bacterial biopesticides

Examples of Commercially Exploited Bacterial Bioinsecticides and their Mode of Action

(i)Bacillus thuringiensis

The most commonly used bacteria for commercial biopesticide formulation are the spore

forming bacteria Bacillus thuringiensis. It is the mostly used around the globe as an effective and

safe insecticide for insect pest in agriculture, forestry, medicine (Jurat-Fuentes and Jackson,

2012; Peralta and Palma, 2017). They are used to control insects belonging to Lepidoptera,

Diptera, Coleoptera and Hymenoptera. The common serovars of Bacillus thuringiensis known

for their insecticidal activities are kurstaki, aizawai, sandiego and tenebrionis. The serovar Bt

var. israelensis, is used to control mosquito vectors of human diseases (Seleena et al., 1997).

The bacteria produce toxic proteins during endospore formation which are cidal to the insects.

During the sporulation phase the parasporal bodies of these bacteria synthesize crystal toxins Cry

and Cyt belonging to the δ endotoxin class of bacterial proteins (DeMaagd et al., 2001; Bravo et

al., 2007). These proteins results in pest mortality via solubilization, proteolysis, specific

binding, pore formation and larval death. These proteins when ingested by the insects bind

specifically to insect midgut receptors and alter the osmotic balance in epithelial membrane

triggering pore formation and cell lysis in gut wall leading to leakage of gut contents ultimately

resulting in starvation and death of insect (Rodrigo-Simon et al., 2008; Heckel, 2012).

(ii)Bacillus sphaericus

Bacillus sphaericus is gaining interest as a competent substitute to conventional insecticides in

mosquito larval control programs. It is reported to have insecticidal activities against larvae of