Biological control of insect pests
Biological Control is the beneficial action of living organisms that reduce population density of insect pests and control their damage. The organisms used in Biological Control -usually called natural enemies- are typically divided into predators, parasitoids and pathogens. Predators eat more than one prey item in order to grow and reproduce, where the majority of them are predatory as both larvae and adults. Ladybird beetles are some important insect predators. These species belong to the order Coleoptera of the family Coccinellidae and are preying mainly on aphids and scale insects.
Unlike predators, parasitoids complete their development on or within a single host (and ultimately kill the host), where adults live outside the host. The insect parasitoids are belonging mainly to orders Hymenoptera and Diptera.
The life cycle of a parasitoid insect is presented –in summary- in the figure below.
Entomopathogenic microorganisms cause diseases to insects. Insects are mainly infected by fungi, bacteria, protozoa, viruses and nematodes. These pathogens are usually applied in the field using conventional sprayers. One of the most common used entomopathogenic agent is the bacterium Bacillus thuringiensis, that is used against larvae of Lepidoptera, mosquitoes, Diptera and Coleoptera.
|Beauveria bassiana (left)and Metarhisium anisopliae (right)on Rhynchophorus ferrugineus larvae|
|Beauveria bassiana (left)and Metarhisium anisopliae (right) on Rhynchophorus ferrugineus adults|
Biological Control is generally divided into Natural Biological Control (action of natural enemies without human involvement) and Applied Biological Control (action of natural enemies after human involvement). Applied Biological Control is further divided into Population Management (breeding, mass production and releasing of indigenous natural enemies) and Classical Biological Control (introduction and management of populations of exotic natural enemies or the use of microbial preparations).
The first and perhaps the most successful classical biological control case involves the predatory coccinellid Rodolia (Vedalia) cardinalis,
against the citrus insect pest, Icerya purchasi. Another more recent example of classical biological control in Greece involves the use of Cales noacki, a parasitoid native to Central and South America, against the wooly whitefly, Aleurothrixus floccosus. Cales noacki was introduced in Greece in 1991. The breeding and mass production of the parasitoid was conducted in the Benaki Phytopathological Institute, where afterwards several releases were carried out in citrus groves, where the presence of the wooly whitefly was observed.
The management and facilitation of the action of natural enemies can be provided in different ways in order to enhance their effectiveness. In this task, the conservation of natural enemies can be achieved by providing them with necessary resources and/or protecting them from toxic chemicals. Also, periodic releases of natural enemies, usually called augmentation, are often desirable, especially in greenhouse conditions. For this purpose, laboratory mass production and subsequent release of the natural enemies are conducted.