Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

_____________________________________________________________________Ecology of insect pests and natural enemies4.10 Purchase and Release of Natural EnemiesIn several countries in Asia, commercial or non-commercial insectaries rear and market a variety ofnatural enemies including several species of parasitoids, predaceous mites, ladybeetles, lacewings,praying mantis, and pathogens such as NPV (virus), and Trichoderma. Availability of (commercially)available natural enemies in a country also depends on the regulations of each country regardingregistration (Regulatory Affairs).Numerous examples from Asia exist on the use of reared natural enemies for release in the field. Ineggplant, good results have been reported with egg parasitoid Trichogramma sp. for the control of fruitand shoot borer (Leucinodes orbonalis). When Trichogramma chilonis was released at fortnightlyintervals in study in Tamil Nadu, India, it significantly reduced pest damage and produced fruit yield of20.30 t, compared to the control yield of 13.06 t (Raja, 1998). Trichogramma japonicum was released ineggplant field in a study in Andhra Pradesh, India, and resulted very good control of shoot and fruit boreras compared to control (Sasikala, 1999). Check with your Extension Service or Biocontrol Agencies foravailability of these natural enemies.Introduction of natural enemies is often a long process that includes training in parasitoid rearing,establishing an efficient rearing facility, setting up (field) experiments and farmer training (Ooi, Dalatreport, 1999). Success with such releases requires appropriate timing (the host must be present or thenatural enemy will die or leave the area) and release of the correct number of natural enemies per unitarea (release rate). In many cases, release rates vary depending on crop type and target host density.This guide does not make specific recommendations about the purchase or release of the (commercially)available natural enemies, but it does provide information about the biology and behavior of somecommercially reared species that are important for eggplant insect and disease control. This informationcould be helpful in making decisions regarding their use. See chapter 6. In addition, addresses ofinstitutions providing or marketing natural enemies in Asia can be found in manuals such as “TheBiopesticide Manual” (BCPC, 1998) and on several sites on the Internet, for example that of the USdepartment of Agriculture, at www14 and www15 (see reference list).4.11 Management and control activities for pest insectsNext to biological control by natural enemies, pest populations may be managed by other methods. Theuse of insecticides is a common alternative but there are other options that may be valuable. Some ofthese options are listed in this section.Specific management and control practices, like many cultural methods, that are important for managingpest insect populations in the field are mentioned in the next chapter, for each pest insect individually.4.11.1 Use of insect nettingCultivation under “net houses” is increasingly receiving interest. A net house, or insect cage, is a frame ofwood a little higher than the eggplants, covered with fine mesh netting. The netting prevents insectsentering the crop from outside, particularly lepidopterous pests like moths and butterflies but also aphidsmay be prevented from entering the plants when the netting is fine enough. Net houses do not preventinsects coming from the soil like cutworms. Often, the net houses are placed over nurseries, to preventdamage from caterpillars to the young plants. Also, in eggplant, net houses on nurseries can providegood initial control against jassids which may carry little leaf disease.Net house: plants in, pests out!Good experience with the use of a net house in eggplant was obtained from afield study in Bangladesh. A net house was made out of bamboo poles andnylon nets. Plant left-overs and pupae found in the top layer of the soil wereremoved before placing the net house over the eggplants. Less insect infestationof shoots and fruits was found on the net house plants as compared to theuncovered plants.Unfortunately, some of the studies were not successful because the nets werestolen from the field…! (pers. comm. Prabhat Kumar, 1999, Bangladesh).58Eggplant Ecological Guide