Cabbage Integrated Pest Management : An Ecological Guide.

Major Natural Enemies of Cabbage Insect PestsPrimary Œ or secondary ???When you leave a plate of food with for example some chicken meat in your kitchen and leave it fora few days, you may find the meat covered with fungus when you look again. This fungus is called asecondary infection: it was not the reason the chicken died (the chicken was probably killed formeat) but it came in after the chicken was dead.Similarly, when insects are dead, some fungi may start growing on the dead insect. This is alsocalled a secondary infection. These fungi that cause secondary infection are part of the “trashmenteam” of nature: they make sure dead things are decomposed quickly. When the fungi actuallycause a living insect to die, like insect-pathogenic fungi do, it is called a primary infection.Interesting, but why bother?When searching for beneficials in the field, it is important to distinguish between pathogens causingprimary infection and those causing a secondary infection. Insects with a secondary infection mayoften be already partly decomposed.Knowing that there is a fungus controlling pest insects in your field, should make you extra carefulwhen considering pesticide applications, especially fungicides. Fungicides can quickly kill the beneficialfungi!How to use this…?When a primary infection is suspected and there are many insects dead and covered with fungus,you can consider making your own bio-insecticide from these dead insects. Collect as many as youcan find in the field, put them in a jar with water, crush them a little and stir firmly. This will releasefungus spores into the water. Filter the water slightly to remove large insect parts. The remainingsolution can be used to test its effectiveness in insect zoos. Spray the solution over insects that areplaced in a jar. Check if these insects become infected over the next days. Use water as a control.See also box in section 4.9. If it works, similar solutions can be applied to the field. It might giveadditional control of pest insects.J Free help from Mother Nature!Mode of action and symptomsFungi penetrate the skin of insects. Once inside the insect, the fungus rapidly multiplies throughout thebody. Death is caused by injury to the tissue or, occasionally, by toxins produced by the fungus. Thefungus emerges from the insect’s body to produce spores that can sometimes be seen as a “dusty”appearance. When spread by wind, rain or contact with other insects, the spores can spread the infection.Infected insects stop feeding and become lethargic. They may rapidly die, sometimes in a position stillattached to a leaf or stem. The dead insect’s body may be firm or it may be an empty shell. The fungusis often seen as “hairs” or “dust” in various colors around the insect’s body or on parts of the body.EffectivenessInsect-pathogenic fungi usually need moisture to cause infection. Natural infectionsare therefore most common during the wet season. The effectiveness of fungi againstinsect pests depends on many factors: having the correct fungal species with thesusceptible insect life stage, at the appropriate humidity, soil texture (to reach grounddwellinginsects), and temperature. The fungal spores which can be carried by windor water, must contact the pest insect to cause infection. When insect-pathogenicfungi are applied, for example through a spore-solution, good spray coverage of theplants is essential.caterpillar wilt129 Cabbage Ecological Guide - 2000