Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________Major Natural Enemies of Eggplant Insect PestsEffectivenessTrichogramma are particularly good natural enemies because they parasitize and kill the pest in the eggstage, before the crop is damaged. Activity of Trichogramma can be recognized by monitoring black(=parasitized) egg-masses.Naturally occurring populations of Trichogramma species are known to be important control agents ofmany crop pests. Trichogramma wasps that are mass-reared for release in the field sometimes giveineffective parasitism for many reasons. The choice of host species is one factor. They are sometimesreared on other insects than the ones they should parasitize in the field and this may result in adults thatare not able to recognize and parasitize the pest. Also, the field conditions at the time of release areimportant: there should be host eggs present, heavy rain shortly after the release will wash off theparasitoid eggs, etc. The number of wasps released (the release rate) is another important factor.Trichogramma wasps are usually released on small cards containing parasitized egg masses(“Trichocards”). Check with supplier how many cards are needed for a field and where they should beplaced.Regular field monitoring is essential for the success of Trichogramma.ConservationSpraying insecticides, especially broad-spectrum insecticides, is the surest way to eliminate the tinywasps. When Trichogramma is active (and especially when it is released into the field) and blackparasitized egg-masses are found in the field, avoid spraying insecticides.6.3 PathogensPathogens are bacteria, viruses, fungi, and nematodes. Insects, like humans andplants, can be infected with pathogens which cause diseases. Insect pathogensgenerally kill, reduce reproduction, slow the growth or shorten the life of a pestinsect. Under certain conditions, such as high humidity or high pest populations,these pathogens can cause disease outbreaks that reduce an insect population.This is why such pathogens can be considered natural enemies of insects. Mostinsect pathogens are specific to certain groups of insects and certain life stagesof the insect. Some microbial insecticides must be eaten by the target pest to beeffective, others work when in contact with the target pest.Unlike chemical insecticides, microbial insecticides usually take longer to kill or weaken the target pest.Most insect pathogens are not harmful for other beneficial insects, ☺and none are toxic to humans.Pathogens are most effective when pest populations are very high. Pathogens are difficult to managebecause their presence and effectiveness strongly depends on factors like temperature and humidity.Most pathogens are too small to be seen by human eyes. Only the symptoms that insect-pathogenscause can be seen with the eyes: for example a dead insect covered with fungus spores like “hairs” or“dust” or a dead insect which is black and spills fluid out of the body.Some pathogens have been mass produced and are available commercially for use in standard sprayequipment. These products are often called biocontrol agents, microbial insecticides, microbials, bioinsecticidesor biopesticides. Some of these microbial insecticides are still experimental, others havebeen available for many years. The best known microbial insecticide is probably the bacterium Bacillusthuringiensis or Bt which is available in many different formulations. NPV is increasingly being used inAsia because it can be produced on-farm. There is no NPV available for eggplant insect pests to date.Microbial insecticides can be used together with predators and parasitoids. Beneficial insects are notusually affected directly by the use of a microbial insecticide, but some parasitoids may be affectedindirectly if parasitized hosts are killed.Below, some pathogens of eggplant insect pests are described.109Eggplant Ecological Guide