Predators, insect control

There is evidence, moreover, that higher population densities and increased survival of some insect pests follow chemical treatments designed to control them. This is because such treatments result in the destruction of predator insects that naturally control pest populations. Killing the predators only increases the needs for future insecticide treatments. ... 

Rapusas, H. R., Bottrell, D. G. and Coll, M. (1996). Intraspecific variation in chemical attraction of rice to insect predators. Biological Control 6 394-400. 

The toxicity of these materials has led to the development of alternative means of insect control. Pyrethrins are natural insecticides produced by plants to ward off predators. Over the past decade or so, more of these natural defenses called allelochemicals have been investigated in the hopes of using them commercially. See the ASIDE on pyrethrins. 

Insect control is restricted to natural insecticides derived from plant extracts, such as pyrethrum or derris. Biological controls such as Bacillus thuringiensis and predator... 

Several seasons of field testing have shown a number of advantages in the use of the antifeeding approach to insect control. First, it is selective. Antifeeding compounds affect only pests which feed on the crop protected. Parasites and predators which walk over the treated foliage or feed on the affected insects are not killed, as with conventional insecticides. Honey bees and other pollinators are not affected by toxic deposits. 

Our experience did show, however, that the antifeeding approach to insect control appears both practical and acceptable. The compound was harmless to all but the pests being controlled, and it fitted in well with the integrated control type of program in which parasites and predators are disturbed as little as possible. 

The natural ecosystem maintains a delicate balance between pests and predators. Pest insects can be controlled by the artificial release of predators. One example is a parasitic wasp, Diadegma insulare. The adult female wasp lays eggs in a Plutella xylostella larva and pupates inside the cocoon of the mature larva. This and other insect predators are available commercially, but the usage is limited. Protozoa and nematodes are also used in insect pest control. One example of a protozoan that effectively infects locusts and controls the population is Nosema locustae. A commercially available nematode insect control agent is Steinemema carpocapsae. This nematode parasitizes scarab larvae with a symbiotic Photorhabdus bacterium that produces insecticidal toxins. 

Biological predators. This method consists of releasing a biological predator to control the insect pest. In the United Kingdom its only successes have been in enclosed environments such as glasshouses. However, the technique was used very successfully nearly 100 years ago in California when the Australian ladybird beetle was introduced as a predator for cottony cushion scale which was ravaging citrus trees. 

Pyridalyl controls a wide variety of lepidopterous pest strains such as the diamondback moth (Plutella xylostella) which is resistant to various existing insecticides (8). This insecticide is also effective against thysanopterous pests. Moreover, it does not exert an adverse effect on various beneficial arthropods such as natural predator insects (e.g., Oristar-A ) and honeybees. Therefore, this novel insecticide is expected to be a usefiil material for controlling lepidopterous and thysanopterous pests in IPM and insecticide resistant management programs. 

Biological and Natural Controls. Parasites and predators are effective in limiting the numbers of pest Insects and plant pathogens both in nature and for crops (35). This basic fact led to the development of biological controls. For example, the vedalia beetle, which was Introduced for control of cottony cushion scale on citrus in California, has provided continuous effective control of this pest for many decades. Worldwide only approximately 1% of the pests have been effectively controlled by Introduced biological control agents (43). 

The widespread use of economic poisons has a definite impact on the animal complex on the face of the earth which provides our sustenance. Already we have seen the use of DDT for codling moth control on apples result in a relatively minor pest becoming a serious threat. The same material used as a wonder spray for fly control now fails, after a couple years of common usage, with the appearance of new, resistant strains of flies. Bees and other pollinating insects as well as helpful predators or parasites may be decimated and their important aid be lost by untimely or improper use of most of the newer insecticides. 

One of the best illustrations of high specificity is di(4-chlorophenoxy) methane (Neo-tran), which has been used for some time commercially in the field, principally for the control of the citrus red mite. So far there has been no indication of undesirable effect upon pollinating insects or on desirable predators or parasites. 

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