WHAT IS PESTICIDE RESISTANCE ?

Natural and artificial selections

Pesticide resistance is the ability of a pest to tolerate a pesticide that once controlled its numbers. Look at Figure 1 below: Figure 1 The use of pesticides is prevalent in all types of agriculture, but particularly so in commercial agriculture. Repeated use of the same class/type of pesticides to control a pest can lead to the promotion of certain characteristics within the population of the pest. When a pesticide is first used, a small proportion of the population may survive the exposure due to some form of variation in their genetic make-up. These individuals then reproduce and pass on the adaptations to the next generation. As the farmer continues to use the pesticide, the proportion of the population of those individuals with the adaptation to survive will increase. In other words, the population of individuals with resistance increases with respect to the population without, and soon only those with the resistance will exist. Worldwide, more than 500 species of insects, mites and spiders have developed some level of pesticide resistance.

ARTIFICIAL SELECTION

Definition: This is the process by which genetics has been used to promote desirable characteristics in plants and animals that are used by humans in agriculture, horticulture and for companionship.

The process often involves cross-breeding related organisms with desirable traits in order to produce an organism with the combined traits. Through artificial selection, only organisms that have greater yields, grow faster and have resistance to diseases, are allowed to produce offspring. In this type of selection, the environment plays a minor role in the selection process, since the characteristics that are transmitted are selected by humans. For example, cows are bred for the quantity of milk that they produce or the quantity and quality of meat that they produce. One example is the Jamaica Hope, which was developed in Jamaica to satisfy the need for a cow that could thrive under tropical conditions and which would also produce large volumes of milk. Another, the Jamaica Red, is a breed of beef cattle that was developed in Jamaica to produce cattle that could produce quality beef.

All of the cereals that we now enjoy were developed from wild grasses. Many of our agriculture crops, for example sugar cane, are still undergoing artificial selection in order to produce betteryielding varieties. Horticulturalists are also using artificial selection to produce plants with larger blooms, with resistance to diseases and with flowers with different colours.

Artificial selection is also termed selective breeding in some texts. The science is the same, however, and both terms are used interchangeably. Artificial selection can lead to too much inbreeding (remember that the organisms are genetically similar), resulting in a reduction in variation between organisms. It can also result in harmful recessive alleles being passed on to succeeding generations since, as mentioned previously, closely related individuals are interbreeding.

HOW DOES IT DIFFER FROM NATURAL SELECTION ?

Artificial selection uses human intervention to determine the characteristic that is to be passed on or enhanced in subsequent generations. In natural selection, variation has to exist among the