Cabbage Integrated Pest Management : An Ecological Guide.

Major Natural Enemies of Cabbage Insect Pestscultures from laboratories or commercial sources, can be multiplied on-farm. Both in Vietnam and IndonesiaNPV is locally reproduced by IPM farmers with mixed results. Quality control issues remain an importantaspect of on-farm reproduction of NPV. See box below.NPV production on-farm: some quality mattersIt was noted that when NPV was multiplied on-farm the virulence of the NPV solution could vary fromone season to the next. In fact, an NPV highly effective in controlling e.g. Spodoptera sp. in oneseason could give low control in the next season, when diseased caterpillars were used to make anew NPV solution. A number of issues may contribute to this:· When wild insects (from the field) are used to prepare NPV solutions, it can be difficult to distinguishlarvae of susceptible and non-susceptible species. For example, In India and Thailand, larvae ofH. armigera, Spodoptera exigua and Spodoptera litura can occur together and at the third instar,when inoculation is most effective, they are difficult for untrained observers to distinguish. Mixingdifferent insect species reduces the viability of any one NPV strain.· Wild larvae can themselves be carrying pathogens that may enter the production system andcompete with the NPV. For example, microsporidea and Bacillus sp. can be difficult to distinguishfrom NPV unless staff are well trained. Co-infection with other pathogens may reduce the “yield”of NPV.· When fresh leaves are used to feed the larvae, these leaves may also be contaminated withunwanted entomopathogens. These pathogens can reduce NPV production.· When healthy larvae are inoculated, it is important to infect insects at the right stage. Optimizingthe age/weight at infection is crucial to maximizing productivity in individual insects. Also, lastinstar caterpillars are usually unaffected by NPV.Strict quality control procedures are not only essential for product consistency, but also for safety.Where quality control is inadequate, microbial contamination of the final product is inevitable. Inmost of these cases this will merely lead to a loss of efficacy due to dilution of the active ingredientby competing microorganisms. However, it is possible that potential human pathogens may alsocontaminate these production systems. Quantification of the degree of contamination and identificationof these contaminants is important in determining the likely risk to human health. Many low technologyproduction systems (such as many on-farm NPV production areas) in use around the world haveminimal or no quality control procedures. This is an unsatisfactory situation and can damage thereputation of microbial control in addition to posing a serious health risk to those who produce orcome into contact with the product (Jenkins & Grzywacz, 1999).6.3.4 NematodesThere are many species of nematodes (very small worms). Some of them, likerootknot nematodes, attack and damage plants. Other nematode species arebeneficial in that they attack pest insects that live in the soil or that spend sometime of their life cycle in the soil such as beetle larvae, cutworms, and somearmyworms. These nematodes are called 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 roleCabbage Ecological Guide - 2000132