Microbial control

who carried out the first experiments (1884)

The Russians

Commercial preparation of which fugus was available in Paris (1891)

Beauveria

Advantages of microbial control

1. shorter generation time and vast production of progeny

2. can be sprayed from traditional sprayers

3. do not seek out their prey but rely on chance contact

4. no toxic residues

5. very selective

6. resistance development is unlikely

7. compatible with pesticides

8. ease of genetic modification

1. Disadvantages of the microbial control

1. Logistically difficulties

2. Many potential pathogens, such as Coelomomyces sp (fungi)

3. Do don’t disperse well in water and so infection rates are very low

4. Specificity can be too high

5. Short life-span

6. Threshold population may be required

7. Ineffective for unsightly insect corpses

8. Problem of development

What are logistically difficulties

its difficult to spray the numerous and scattered resting sites of dipterous vectors, such as mosquitoes and black flies, with pathogens; so control would have to be aimed at their aquatic larvae.

Types of pathogens used in pest control

1. Contact microbes (fungi)

2. Ingested microbes

3. Viruses

4. Bacteria

5. Microsporidia

Contact microbes (fungi)

Results from a spore landing on the cuticle of the insect, and the germ tube then penetrating the cuticle directly. The short distance spores are projected from an insect corpse means that only nearby insects can be infected.

Disadvantages of fungi

Is potentially unreliable, since the spores require moisture to sporulate and really quite high humidities are required for success.

Which fungus is considerably promising for soil application

Metarhizium anisopliae

Ingested microbes

rely on ingestion by their host to initiate an infection. They are therefore adapted to having a fairly resistant stage in the life cycle which enables their survival on relatively dry surfaces, such as a leaf, until ingestion by the pest.

Viruses

More than 300 viruses have been isolated from about 250 important pest insect species, yet less than ten are in commercial production

Disadvantages of viruses as pesticides

1. Have to be cultured in living insect

2. May mutate to attack humans and animals

3. Need to be very widespread

4. Host range within the order may be quite unpredictable

Advantages of Viruses as pesticides

1. Viruses can be applied at very low dosage

2. Naturally occur in nature

3. Specific to the host

4. Easily spread in the field

Most successful pest control viruses are

1. Baculoviruse in the baculoviridae

2. The subgroups nuclear polyhedrosis (NPVs)

3. The granulosis viruses (GVs)

Bacteria

Formulated as powders. The powders are wetted and sprayed, and the pest may then ingest vegetative bodies while feeding. Each bacterial body contains two structures, a spore and a protein crystal (the endotoxin). Although the spore often releases some toxins, the important insecticidal element is the protein of the crystal. When the parasporal body reaches the insect gut, the protein crystal dissolves.

Viruses

Bacteria

The bacterial toxin most commercialized is that of

Bacillus thuringiensis

Microsporidia

Included in the phylum Protozoa. However, most experts now regard them as a separate phylum. The genus Nosema have long been investigated as insect pathogens for biological control.

Disadvantages of Microsporidia

can only be propagated on living insect hosts, which makes their commercial multiplication extremely expensive, also that they are more likely to affect the insect than to achieve a rapid kill.

Microsporidia