Cabbage Integrated Pest Management : An Ecological Guide.

Ecology of Insect Pests and Natural Enemies4.11.11 Pesticide associated problems on insects and natural enemiesDespite the advantages of conventional insecticides, there are numerous problems associated with theiruse. These include:1. The resurgence of pest populations after elimination of the natural enemiesA well-known phenomenon is that when natural enemies are killed by pesticide applications, pestinsects (which often have a high reproduction rate) can increase their numbers very quick. Thiseventually results in yield and quality loss of the crop. Even pest insects that, under no or lowpesticide applications cause no problem (populations are kept low by natural enemies) can causeoutbreaks and yield loss when natural enemies are eliminated, especially insects or mites thathave developed resistance against pesticides. An example is red spider mite, which has manynatural enemies but can cause severe problems in heavily sprayed fields.2. Development of insecticide-resistant populationsThe development of resistance is one of the moreserious problems in pest management.Resistance means an insect can tolerate apesticide without being killed. Many insect pestspecies now have resistance to some or severaltypes of insecticides, and few chemical controloptions exist for these pests.The number one resistant insect is the aphid,Myzus persicae (Homoptera: Aphidae). Thisaphid is resistant to more insecticides than anyother insect. The numbers two and three notoriously resistant are the Colorado potato beetle,Leptinotarsa decemlineata and the diamondback moth, Plutella xylostella. One case ofdiamondback moth resistance against pesticides is described in the box below. In some areas,the diamondback moth has even become resistant to biological control agents like Bt (Bacillusthuringiensis).3. Negative impacts on non-target organisms within and outside the crop systemNumerous cases exist of negative impact of pesticides on humans and livestock. Many farmersparticipating in FFSs have experience with pesticide poisoning, or side-effects on health frompesticides.LNatural enemies are generally more adversely affected by chemical insecticides than the targetpest. Because predators and parasitoids must search for their prey, they generally are very mobileand spend a considerable amount of time moving across plant tissue. This increases the likelihoodthat they will get in contact with the pesticide. They also feed on or live inside poisoned prey. Inaddition to killing natural enemies directly, pesticides may also have sublethal effects on insectbehavior, reproductive capabilities, egg hatch, rate of development, feeding rate, and life span.Cabbage Ecological Guide - 200072