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中文Introduction
Insecticides are used throughout the world to protect against unwanted damage by insects. An insecticide causes death or irreversible damage to the targeted insect by affecting it at any stage in its life-cycle. Insecticides have great importance in the agricultural industry as they can minimise the quantity of crops lost through insect damage, thus insecticide use can increase profits and productivity. There is a large spectrum of commercial insecticides now in use, all with different properties and characteristics (IPMRC, 2006).
An ‘Ideal’ Insecticide
The properties and characteristics of an insecticide are determined by what is will ultimately be used for. This makes it difficult to outline exactly what characteristics an ‘ideal’ insecticide would possess. As a consequence the desirable characteristics are fairly generic and generalised.
In an agricultural context, an ‘ideal’ insecticide would be one which has a broad range of uses. For example, the insecticidal agent would be suitable for use on cereal crops as well and fruit crops.
When using the insecticide, there should be minimum harm and disturbance to the natural environment (Sanborn, 2006). It would also be specific to the pest insects whilst conferring no toxicity to beneficial insects, micro-organisms, animals, or humans. There would be no accumulation issues within the food chain so no other organisms are affected except those insects targeted.
Application of the insecticide should be uncomplicated and one application should be enough to protect the crop from the offending insects. The insecticide itself should be easy to store and handle, with a high efficacy therefore only small amounts of insecticide are used.
After the insecticide has been applied, the ‘knockdown’ rate or speed of action should be rapid. For example, the ‘knockdown rate of the insecticide HERO™ is 12 hours (FMC, 2006). This means the insecticide starts killing the insects immediately. For this to be achieved, the insecticide would need to be targeted to an active part of the insects’ life-cycle.
Once the insects have been killed, the insecticide chemical itself should decompose quickly into a non-toxic compound. This decomposition time should be as short as possible whilst maintaining the insecticide activity for the necessary duration of time to fully protect the crop.
Production and manufacture of the ‘ideal’ insecticide should also be a consideration as a simple and relatively easy chemical to manufacture will mean a lower costing insecticide. The shelf-life of the chemical should also be long and storage conditions easy to achieve, thus bringing the overall cost of the insecticide down.
Reasons for such characteristics
A broad-spectrum insecticide would be extremely useful as this reduces the number of different insecticides necessary. It simplifies the process of choosing which insecticide is most appropriate and removes the possibility of poor or badly selected chemicals.
It is desirable for the ‘ideal’ insecticide to possess specificity towards only the ‘pest’ insects and to no other. This is vitally important as there are a great many beneficial insects that live on crop plants. Also, any disturbance in the population of organisms can impact on natural ecosystems. This unbalance can have repercussions on all aspects of animal and plant life. For example, a compound which kills insects but also harms other wildlife would be unacceptable as an insecticidal agent.
Protecting humans from insecticidal poisoning is of paramount importance when developing a new insecticide. If humans are exposed to the insecticide then there should be no toxic effects experienced. Unfortunately in the past this has not been the case and there is a large weight of evidence supporting the fact that toxicity from chemicals can cause disease in humans (Mukerjee 2006). These effects may be carcinogenesis, neurotoxicty, and reproductive and developmental effects (Hodgson and Levi, 1996).
Another aspect to consider is the accumulation of compounds within the food chain. An ‘ideal’ insecticide would kill the desired insects and then rapidly decompose to a harmless compound which does not enter the food chain. As was seen in the 1960s, an insecticide called Dichlorodiphenyltrichloroethane (DDT) accumulated in higher organisms within the food chain (Morisawa 2002). This caused fatalities and disease in animals and in humans. This is why it is important that the insecticide is non-toxic and decomposes therefore does not accumulate in the environment.
To further reduce risk of toxicity and increase ease of storage, a high efficacy insecticide would be the best choice. This means less chemical would be used to achieve the desired effects on the target insects. To further increase this efficacy, the insecticide would be fast-acting therefore work immediately, thus reducing damage to the crop plants. A chemical that only requires one application would be ideal as this reduces the overall cost of using the insecticide and also make the application of the insecticide easier.
Developing a new insecticide means that resistance it is necessary to keep in mind the possibility of insects developing resistance to the new chemical (Ceccatti, 2004). Ideally, there would be no chance of resistance being developed. Insects can build up a resistance to insecticides and this renders the insecticide much less effective. If the chemical used was such that it was extremely difficult to develop resistance against it, then this would ultimately give the insecticidal agent a longer life and therefore a more lucrative investment for the manufacturing company.
Production and manufacture of the insecticidal compound should be easy and safe. The compound itself should be simple in structure so that there are as few stages of production and possible. This makes the process of production much cheaper, again keeping the cost of the insecticide as low as possible.
Obstacles and Problems
It is difficult to design a chemical which possess all the desirable characteristics of an ‘ideal’ insecticide. The chemical itself may need to be very complex in molecular composition in order to confer specificity to its target organisms. This can make manufacture of the compound difficult and costly. Designing a novel compound which has never been discovered before can be difficult in itself. The compound must not only be capable of killing insects but it must also consider the insect physiology and even evolutionary genetics (Ceccatti, 2004)
Resistance has been a major obstacle with many insecticides and pesticides in use today. Insects have become resistant to many of the chemicals targeted towards them. If the insects develop resistance to the insecticidal agent then this may ultimately mean the agent can no longer be used. Alternative approaches may need to be considered and industry may need to take a different perspective with regard to insect control in the future (Ceccatti, 2004) (IPMCR, 2006).
Insecticides are toxic and it is almost impossible to target chemicals so specifically that only certain unwanted insects are affected. This means there will always be some destruction of desirable organisms. Insect specificity can be very hard to achieve, particularly when specific insect need to be targeted. This can pose problems when developing an insecticide as generally the compound will be toxic not only to insects but also other organisms. This means consideration must be given to any situation before applying insecticides (Sanborn 2002). There must always be a balance between crop destruction and the risk of harm to the environment. Any chemical put into the environment will have an effect on the overall ecosystem. It is therefore desirable to only use insecticides when it is absolutely necessary to limit crop destruction. This is a potential problem faced by chemical companies as the insecticide may be used less often. As new techniques for insecticidal control are introduced then this also affects the market potential for an insecticidal agent.
