Problem 7 - Campbell Biology

Question

Mosquitoes resistant to the pesticide DDT first appeared in India in \(1959,\) but now are found throughout the world. (a) Graph the data in the table below. (b) After examining the graph, hypothesize why the percentage of mosquitoes resistant to DDT rose rapidly. (c) Suggest an explanation for the global spread of DDT resistance. $$\begin{array}{|l|c|c|c|}\hline \text { Month } & 0 & 8 & 12 \\\\\hline \text { Mosquitoes Resistant* to DDT } & 4 \% & 45 \% & 77 \% \\\\\hline\end{array}$$

Step-by-Step Solution

Answer

The rapid increase in DDT-resistant mosquitoes is due to natural selection, and the global spread is facilitated by human transportation.

Step 1 - Plot the Data on a Graph

Create a graph with the x-axis representing the months and the y-axis representing the percentage of mosquitoes resistant to DDT. Plot the points (0, 4%), (8, 45%), and (12, 77%) on this graph.

Step 2 - Connect the Points

Draw lines connecting the points (0, 4%), (8, 45%), and (12, 77%). This will visually show the trend of the data over time.

Step 3 - Analyze the Graph

Examine the graph to observe the trend. Notice how the percentage of mosquitoes resistant to DDT increases rapidly over the months.

Step 4 - Hypothesize the Rapid Increase

The rapid rise in DDT-resistant mosquitoes can be hypothesized as resulting from natural selection. Mosquitoes resistant to DDT survive and reproduce, passing on the resistance genes to their offspring.

Step 5 - Explain the Global Spread

The global spread of DDT resistance can be explained by the transportation of people and goods, which can carry mosquitoes from one place to another, thereby spreading the resistant population worldwide.

Key Concepts

natural selection

In the context of DDT resistance in mosquitoes, natural selection plays a crucial role. When DDT is applied in an environment, it kills most mosquitoes that are not resistant. However, a small percentage of mosquitoes may have genetic variations that make them resistant to DDT. These resistant mosquitoes survive and reproduce.

Over time, the offspring of these resistant mosquitoes will inherit the resistance traits. As a result, successive generations will have a higher proportion of DDT-resistant mosquitoes. This process is natural selection at work—favorable traits (resistance to DDT) become more common in the population because they provide a survival advantage.

Key points to remember:

• Mosquitoes with DDT resistance genes survive and reproduce.
• Resistant traits are passed on to offspring.
• Over generations, the population consists increasingly of resistant mosquitoes.

Natural selection ensures that only the fittest organisms survive in the face of environmental stressors, such as pesticide application.

global spread of resistance

The spread of DDT-resistant mosquitoes is not restricted to one region. This resistance has become a global phenomenon, largely due to human activities. Here are some reasons for the global spread:
Transportation: Mosquitoes can travel across regions via vehicles, ships, and airplanes. When people move, they may unknowingly carry mosquitoes in their luggage or through other means, spreading them to new locations.
Trade and Travel: Global trade and increased travel mean that goods and people frequently move from one part of the world to another. This movement facilitates the unintended spread of resistant mosquitoes.
Climate and Habitat: Mosquitoes thrive in warm, humid climates, which are found in many parts of the world. When they spread to these areas, they can establish new populations quite easily.

The global spread of resistance means that combatting DDT-resistant mosquitoes requires international cooperation and strategies that go beyond local control measures.

pesticide resistance

Pesticide resistance in mosquitoes is a significant issue and occurs when these insects develop the ability to survive exposure to pesticides like DDT. This resistance can develop through several mechanisms:
Genetic Mutations: Random genetic changes in some mosquitoes can make them less susceptible to pesticides. These mosquitoes survive and pass these traits to their offspring.
Biochemical Defenses: Some mosquitoes produce enzymes that can break down pesticides before they cause harm.
Behavioral Changes: Mosquitoes may change their behavior to avoid areas treated with pesticides.

Resistance to pesticides poses a challenge for public health, especially in controlling mosquito-borne diseases like malaria and dengue fever. To tackle pesticide resistance, integrated pest management strategies are essential. These strategies include:

• Rotating different types of pesticides to prevent resistance development.
• Using biological control methods, such as introducing natural predators.
• Implementing environmental management practices to reduce mosquito breeding sites.

Understanding and managing pesticide resistance is vital for effective mosquito control and reducing the spread of mosquito-borne diseases.