Precaution must be taken and research must be done to understand and help prevent resistance with Bt. There are some steps Bt users apply to minimize resistance. Currently in the field, the diamondback moth is the only insect found to have developed resistance against Bt.
The diamondback larvae feed on all plants in the mustard family, including canola, mustard, broccoli, and cabbage. The diamondback moth larvae is resistance to proteins made by the Bt strain kurstaki. In the laboratory, scientists have found many species of insects to be resistant to Bt.
These insects are currently studied to further our understanding of Bt resistance and prevention. Farmers that use Bt are required by the EPA to take steps to help prevent further resistance by other insects. Some alternate Bt applications with synthetic insecticides so that any resistance to any one class of insecticide does not develop.
Individuals with genes that improve their survival will be more likely to pass along these genes compared to the rest of the population. The mix of genes in a population is called the gene pool. The composition of the gene pool continually changes over time through a process called natural selection.
With the help of plant breeders, fruit growers have taken advantage of the gene pool's natural variability in a process known as artificial selection. The first step in this process is to identify desirable traits, such as flavor, color, tolerance, or resistance to a pest. Once desirable traits are identified, these can be incorporated into new crop varieties through conventional breeding or genetic engineering.
For example, apples have been bred to create a few varieties that are resistant to apple scab. Even without specific breeding efforts, fruit crop varieties display a natural range of resistance to various pests and diseases. When monocultures of single varieties are planted, efficiency of production is traded for diversity of resistance to pests. Repeated use of the same class of pesticides to control a pest can cause undesirable changes in the gene pool of a pest leading to another form of artificial selection, pesticide resistance.
When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population. Through this process of selection, the population gradually develops resistance to the pesticide. Worldwide, more than species of insects, mites, and spiders have developed some level of pesticide resistance.
The twospotted spider mite is a pest of most fruit crops and is notorious for rapidly developing resistance to miticides. Every new insecticide group, such as cyclodienes, carbamates, formamidines, organophosphates, pyrethroids, even Bacillus thuringiensis , have developed resistance populations of insects or mites within 2 to 20 years.
The impact of this has been felt throughout the world wherever insecticides are used, in terms of increased vector-borne disease, increased pesticide hazards in the environment, crop losses and poorer quality of products, increased production costs, pest resurgences and rise of secondary pests, and various socioeconomic repercussions.
Worldwide, more than species of insects, mites, and spiders have developed some level of pesticide resistance. The two spotted spider mite is a pest of most fruit crops and is notorious for rapidly developing resistance to miticides. Resistance increases fastest with increasing of temperature, where insects or mites reproduce quickly, there is little or no immigration of susceptible individuals and the user may spray frequently.
Pest control tactics should therefore take account of the possibility of resistance evolution. One of the best ways to retard resistance evolution is to use insecticides only when control by natural enemies fails to limit economic damage.
Repeated use of the same class of pesticides to control a pest can cause undesirable changes in the gene pool of a pest leading to another form of artificial selection, pesticide resistance. When a pesticide is first used, a small proportion of the pest population may survive exposure to the material due to their distinct genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent uses of the pesticide increase the proportion of less-susceptible individuals in the population.
Through this process of selection, the population gradually develops resistance to the pesticide. Insecticides are organized into classes—organophosphates, carbamates, pyrethroids, neonicotinoids, etc. MOA is the specific process by which an insecticide kills an insect, or inhibits its growth.
Selection for resistance can occur if a small proportion of the insect population is able to survive treatment with insecticide. These rare resistant individuals can reproduce and pass on their resistance to the offspring. If an insecticide with the same mode of action is repeatedly used against this population, an even greater proportion will survive.
Ultimately, the once-effective product no longer controls the resistant population. Resistance may develop to only a single insecticide. However, it is more common for insects that exhibit resistance to one insecticide to be resistant or develop resistance more rapidly to other insecticides with the same MOA.
This phenomenon is known as cross-resistance. A closely related phenomenon, multiple resistance, occurs in insect populations that resist two or more insecticide classes with unlike modes of action.
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