Chetana Aggarwal

Characterization of putative virulence factors of Serratia marcescens strain SEN for pathogenesis in Spodoptera litura

Two Serratia marcescens strains, SEN and ICC-4, isolated from diseased insect cadavers were observed to differ considerably in their virulence towards Spodoptera litura. The present study was aimed to characterize the possible virulence factors present in the virulent Serratia marcescens strain SEN. Both the S. marcescens strains were evaluated for the presence of various lytic enzymes such as chitinase, lipase, protease and phospholipase. The virulent S. marcescens strain SEN was observed to possess considerably higher activity of chitinase and protease enzymes; activity of phospholipase enzyme was also higher. Although, all the three toxin genes shlA, phlA and swr could be detected in both the S. marcescens strains, there was a higher expression of these genes in the virulent strain SEN. S. marcescens strain ICC-4 showed greater reduction in overall growth yield in the post-exponential phase in the presence of midgut juice and hemolymph of S. litura larvae, as compared to S. marcescens strain SEN. Proliferation of the S. marcescens strain SEN was also considerably higher in foregut, midgut and hemolymph of S. litura larvae, as compared to strain ICC-4. Peritrophic membrane treated with broth culture of the S. marcescens strain SEN showed higher damage as compared to strain ICC-4. The peritrophic membrane of larvae fed on diet treated with the virulent strain showed considerable damage while the peritrophic membrane of larvae fed on diet treated with the non-virulent strain showed no damage. This is the first report documenting the fate of ingested S. marcescens in S. litura gut and the relative expression of toxin genes from two S. marcescens strains differing in their virulence towards S. litura.

A modified semi-synthetic diet for bioassay of non-sporeforming entomopathogenic bacteria against Spodoptera litura

Standard semi-synthetic diet used for rearing Spodoptera litura (Fab) larvae contains many antimicrobials. This diet is not suitable for evaluating non-sporeforming bacteria. We determined the effect of antimicrobials present in S. litura semi-synthetic diet on growth of entomopathogenic Serratia marcescens. Nutrient broth supplemented with four and two times reduced doses of sorbic acid (0.15 g) and methyl parahydroxybenzoate (0.05 g) supported bacterial growth comparable to control medium. No growth could be observed even at five times reduced concentrations of formaldehyde and streptomycin sulphate. Diet for rearing S. litura was modified accordingly and validated using two S. marcescens strains. Larval mortality ranged between 20% and 30% on the standard diet and more than 90% in the modified diet.

Entomopathogenic Nematodes for the Management of Subterranean Termites

Termites cause economic losses by directly injuring and destroying both living and dead vegetation. They can damage right from sowing the crops till harvest. Billions of dollars are spent annually throughout the world to control and prevent termite infestation. Many bacteria, fungi, and nematodes occurring naturally in soils are known to suppress termite activity. Entomopathogenic nematodes (EPNs) and their associated bacterial symbionts are highly specific in their host range and compatible with many pesticides. EPNs, also called beneficial nematodes, are commercially used to control insect pests. These nematodes offer an environmentally safe alternative to chemical insecticides, and a wide range of EPNs are effective against various termite species. Only a limited number of field studies have been conducted using EPNs as control agents for termites. New isolates of EPNs may prove potential against termite pests in the field. This chapter outlines the potentials of entomopathogenic nematodes in termite management.

Potential of Bacillus thuringiensis in the Management of Pernicious Lepidopteran Pests

Microbial products have a long history of safe use and most of the microbial agents are compatible with other methods of pest control. A number of microbial biopesticides have been registered for field application on various vegetables, fruits, and other crops of agricultural, horticultural, and forest importance. During sporulation phase, Bacillus thuringiensis accumulates certain insecticidal crystal proteins which are pathogenic to a number of insect orders. Thousands of toxicogenic strains of B. thuringiensis exist and each strain produces its own unique well-known insecticidal crystal protein. B. thuringiensis is biodegradable and safe to nontarget organisms as the conditions required for complex steps in the mode of action do not exist in mammals or most of invertebrates. Development of agricultural crop varieties that contain B. thuringiensis proteins provides a safe alternative to the use of chemical insecticides. Tobacco and tomato were the first transgenic plants encoding for B. thuringiensis insecticidal crystal protein. The development of resistance to B. thuringiensis toxins is, however, particularly unfortunate. Thousands of B. thuringiensis isolates are available around the world, and fortunately almost all the major insect pests are susceptible to these strains. Moreover synthetic insecticides in combination with biopesticides are economic, effective, and eco-friendly. The aim of this chapter is to focus on the potentiality of B. thuringiensis in the management of pernicious lepidopteran pests and their mode of their interactions to develop the cost-effective medium for the formulation of biopesticides.

Insect Pest Resistance: An Alternative Approach for Crop Protection

From experience with insect resistance caused by synthetic chemical insecticides, it is clear that no single management tactic can provide lasting solutions to the insect pest problem. Biological control is a component of integrated pest management strategies that minimize insecticide spray applications and move towards ecofriendly systems of pest management. Successful utilization of host plant resistance, phytochemical products, pheromones, biological control agents such as predators, parasitoids, entomopathogenic bacteria, virus, nematodes, and fungi can help to control many destructive pests to achieve sustainable crop protection.