Role of Bacteria, Fungi, Baculoviruses and Nematodes in Biocontrol of Crop Pest
The term ‘Microbial control’ was first used by E. A. Steinhaus (1949) to express the pest population management through disease causing micro-organisms. Microbial control includes all aspects of utilization of micro-organisms or their by-products in the control of pest species. In nature, micro-organisms like viruses, bacteria and fungi, protozoa and rickettsiae may perform important roles in the dynamics and natural regulation of insect and mite population.
Definition:
“Microbial control is a phase of biological control concerned with the employment of micro-organisms for the control and reduction of number of animals/plants in a particular area/given population”.
The study of such organisms has been included under ‘Insect Pathology’ which is a broad-based discipline concerned with the study of all aspects of insect diseases as reflected in any abnormal physiological process or condition in any insect. Insect pathogens may be divided into two groups according to the means by which they enter and infect their hosts:
1) Through Ingestion:
It includes bacteria, viruses and protozoa which must be ingested along with food for causing infection and mortality and can be considered similar to chemical insecticides act as stomach poison. The viruses are queue specific in their site of development and they multiply only in certain tissues within the body of the host. Others, including bacteria may fill their hosts purely by the activity of toxins which they produce during growth.
2) Through Integument:
This includes the pathogenic fungi enter their hosts through the outer integument of the insect body. They are more subject to regulation physical factors in the environment since their penetrative stage generally are not very resistant to adverse effects of external condition.
Possibilities of using pathogens in bio-control:
Sr.No. | Particulars | Pathogens | Host |
1 | Bacteria | a) Bacillus popilliae causing milky disease | Japanese beetle |
|
| b) Baculoviruses thuringiensis | Lepidopterous pest |
2 | Viruses | a)Baculoviruses (br) | Lepidopterous pest |
|
| b) Granulosis viruses (Gr.) | Mosquitoes, mites etc. |
|
| c) Nuclear Polyhedrosis Virus (NPV) | Lepidopterous pest |
3 | Fungi | a) Polymycetes | Lepidopterous pest, beetles, aphids, scales, mites etc. |
4 | Protozoa | Nosema locustae | Grasshopper, orthoptera |
|
| Neogregarires | Flies |
5 | Rickettsiae | Rickettsiella popilliae | Wood wasps, Mosquitoes |
6 | Nematodes | a) Steinernema spp. | White grubs |
|
| b) Heterorahbditus spp. |
|
The successful use of disease for insect control depends upon the biology and characteristics of the host insects and the pathogenic micro-organisms as well as the environment. Host insect must occupy the habitats suitable for introduction of a pathogen and they must have habits that enhance the possibilities of infection. Since disease is generally considered as density dependent factor of mortality the insect that live in aggregation or which form large populations are more susceptible to epizootics as compared to the species which maintains low population densities.
The major emphasis in the application of microbes has been to field collect or artificially mass culture a specific insect pathogen and disseminate it when the host is most susceptible to its effect. One approach to introduce and colonize pathogens as permanent mortality factor in the host population. This approach is called the ‘Microbial Introduction’.
Another microbial technique is to make the repeated applications of a pathogens as microbial insecticide for the temporary suppression of insect pests e.g. development of bacterium, Bacillus thuringiensis. This bacterium is produced by fermentation and is formulated as a dust, wettable powder of emulsion. The material is applied like a chemical insecticide. Its effect is short lived and many applications are needed.