Conidia: total conidia, and viable colony forming units (CFU) of entomopathogenic fungi in fertilizers: counting and identification.
Most of the insects that attack crop plants have natural enemies. The use of chemical insecticides has contributed to the selection of resistant insects. Biological control of insect pests producers are faced with fungi, bacteria, viruses, nematodes and protozoa. Entomopathogenic fungi are very important because they can infect insects, develop within them and end their lives, preventing them from generating pests. These fungi can grow in a saprophytic resulting mycelia, conidiophores and conidia. Similarly they can be cultured in laboratories and obtaining propagation elements (conidia) in large amounts to be incorporated into the fertilizer to be distributed to them in crop areas. For this reason, entomopathogenic fungi are very important for the biological control of insects causing crop pests. All insects are susceptible to fungal diseases. To this end, the conidia of some species of fungi fertilizers are incorporated for adding fertilizer to the areas of crops, the fungus from spreading and infecting insect pest causing. Several species of these fungi which are used preferably. Beauveria spp, Metarhizium anisopliae, Lecanicillium (Verticillium) lecanii, Trichodema spp, Paecylomyces lilacinus, among others.. When it is desired to have specific fungi to affect a particular pest, can be obtained in the area of insect crop infected dead to isolate the fungus that has infected, grow them in the laboratory to identify whether the fungus is already available in some fertilizer, or otherwise suspensions of their conidia which can be dispersed in the growing area.
Fungi have the following advantages: 1) may have different types of specificity for a family of insects or certain species .; 2) entomopathogenic fungi can be introduced and colonize an ecosystem, multiplying and renewed continuously, becoming persistent in the ecosystem without new applications .; 3) mixtures can be applied entomopathogenic fungi; 4) does not pollute the environment nor affect humans or other higher animals; and 5) when the fungus does not reach cause insect death, can disrupt the life cycle of the insect. However also have some problems such as: a) they are sensitive to weather conditions such as extreme temperatures, drying or ultraviolet light; b) be retained under more demanding conditions than inorganic molecules to prevent loss of pathogenicity; c) generally they do not kill immediately, but reach good levels of control between one and three weeks after application, although once parasitized insect stops feeding before dying, reducing the damage.
Entomopathogenic fungi infect insects through the outer cuticle, unlike bacteria or viruses that enter orally. Contact between the entomopathogenic fungus and insect occurs randomly and is influenced by the amount of inoculum (conidia) present in the growing area, a favorable environment to facilitate survival of conidia, and the number of insect hosts. Infection occurs when conidia makes contact with the outer surface of the insect (epicuticle integument). Once the interaction has occurred, the conidia germinate, penetrates through the germ tube and develops within the insect. During development inside the insect toxins it generates involving insect death followed by multiplication, generating a mycelium grows outward facilitating the spread of the fungus in the area. Conidia adhesion to a particular insect is specific and therefore not all fungi can affect any species of insect. This is because such interaction is performed by surface molecules insect having ability to interact with other specific molecules on the surface of the insect (proteins, lipoproteins, polyphenols). Preferred sites in the insect surface for infection to occur are the intersegmental regions whose composition and structure are different from the rest of the body surface. When interaction has occurred, the conidia germinate emitting a germ tube penetrates. The penetration is facilitated by the production by the fungus of some enzymes (proteases, lipases, chitinases) altering the cuticle facilitating entry. Once penetration has occurred, the fungus multiplies inside the insect forming hyphae, they invade the entire body cavity of the insect (hemocoel). During multiplication and growth will generate toxins that besides damaging insect cells, inhibit insect defense reactions. Finally the insect dies before the fungus fills its hemocele without the presence of the fungus is observed. Further multiplication makes the fungus colonizes fully converting the insect body into a mummy, resistant to bacterial decomposition, apparently by the antimicrobial action generated by the fungus. Finally emerges outwards primarily when moisture conditions facilitate this . Eta is why sometimes dead insects covered with fungal mycelium, for example whitish when infected by Beauveria spp observed., Or greenish when they have been infected by Metarhizium spp.
Tests in IVAMI:
- Quantification of total conidia in a fertilizer.
- Quantification of viable conidia in a fertilizer.
- Quantification of colony forming units (CFU) in a fertilizer.
- Identification of the species of fungus that exists incorporated into a fertilizer.
- Identification of the species causing the death of insects found in an area known cultivation for fungi whose conidias be incorporated into fertilizer for a particular purpose fungus.
Sample for testing:
- Fertilizer sample (10 to 20 g).
- Coated insects found dead fungal mycelium.
- Similar to the usual fertilizer product conservation conditions.
Delivery of results:
- Quantification of total conidia, conidia and number of viable colony forming units (CFU): 7 to 10 days.
- Identification of fungi: 4 to 5 days.
- Identification of the causative fungus insect death: time required for cultivation and identification: 7 to 10 days.
Cost of testing:
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