Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

__________________________________________________________________Major Natural Enemies of Eggplant Insect Pests6.3.4 NematodesThere are many species of nematodes (very small worms). Some of them, like rootknotnematodes, attack and damage plants. Other nematode species are beneficial in thatthey attack pest insects that live in the soil or that spend some time of their life cycle inthe soil such as beetle larvae, cutworms, and some armyworms. These nematodes arecalled entomopathogenic nematodes.Nematodes have life cycles like insects: they usually mate, lay eggs, and there are several larval stages.Yet, they are often lumped with pathogens and not with insects, presumably because of their symbioticrelationship with bacteria, and because the symptoms they cause look like disease symptoms.Many species of naturally occurring, beneficial nematodes live in the soil and on plant material. The roleof most of these species is not known, but some nematode species have received attention as potentialbiological control agents. Some of these nematodes can be mass produced and are availablecommercially in some countries. These beneficial nematodes do not harm plants, animals and mostbeneficial insects (Gaugler, www8). They harbor bacteria which produce the toxins that eventually kill thehost insect converting it to food for the nematode.The main species of beneficial nematodes include:• Steinernema species (previously called Neoaplectana): There are several species of this nematodeand all of them have a very broad host range. Different Steinernema species carry different strains ofa bacteria. Two important members of Steinernema are (D’Amico, www3):1. Steinernema riobravis - potential against eggplant fruit and shoot borer (Leucinodes orbonalis). Itshost range runs across multiple insect orders. It can be effective against insects such as tomatofruitworm (Heliothis armigera) and mole crickets. This is a high temperature nematode, effective atkilling insects at soil temperatures above 35°C.2. Steinernema carpocapsae - effective against lepidopterous larvae, including cutworms (Agrotissp.), armyworms (Spodoptera sp.), and some other insects such as mushroom flies.Important attributes of S. carpocapsae include ease of mass production and ability to formulate ina state that allows several months of storage under refrigerated conditions.The species S. riobravis is more heat tolerant than S. carpocapsae and does not need to be storedin the refrigerator.• Heterorhabditis species: carries a different species bacterium than Steinernema nematodes butenters and kills insects in a similar way. These nematodes also enter insects through their skins aswell as through natural openings. They have a slightly longer life cycle than Steinernema species andalso a broad host range.Mode of action and symptomsNematodes actively search for suitable hosts, often attracted by the carbon dioxide (CO 2) emitted by theirprey. The third stage nematode larvae are the infectious stage and only these can survive outside thehost insect because they do not require food. The nematodes carry insect-pathogenic bacteria insidetheir gut. Different nematode species carry different species of bacteria. Once the nematode penetratesits host, usually through the mouth, the anus or breathing holes, the bacteria multiply and kill the insect.The nematodes feed on the bacteria and on the insect tissue, then mate and reproduce. After 6 to 10days, young nematodes emerge from the dead insect to seek out and colonize new hosts.Affected insects usually die within 1 or 2 days. Those killed by Steinernema species turn brown-yellow incolor from the bacterial infection. The insects are very soft, and easily crack. Insects killed byHeterorhabditis nematodes become red and gummy.114Eggplant Ecological Guide