Biological control, a technique used to combat species that cause damage and harm to humans, is used to combat the caterpillar that feeds on cotton leaves. Some species of butterfly lay their eggs in this culture. The microvespa Trichogramma sp. introduces its eggs into the eggs of other insects, including those of the butterflies in question. Wasp embryos feed on the contents of these eggs and prevent butterfly larvae from developing. Thus, it is possible to reduce the population density of butterflies to levels that do not harm the culture. The biological control technique performed by the microvespa Trichogramma sp. consists of:

1. introduction of a parasite or predator in the environment of the species to be fought.
2. introduction of a lethal gene in butterflies in order to decrease the number of individuals.
3. competition between the butterfly and the microvespa to obtain resources.
4. modification of the environment to select better adapted individuals.
5. application of insecticides in order to reduce the number of individuals to be fought.

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One of the alternatives to replace the use of insecticides in agriculture is biological control. This technique consists of:

1. use a particular species to fight a pest.
2. use fungi to produce antibiotics, and these are used as a medicine.
3. prepare the soil with agricultural techniques that involve green manure.
4. contaminate the soil with an industrialized substance to specifically combat pests.
5. prevent the growth of pests by the use of industrialized repellents, which do not kill them but cause them to leave the agricultural area.

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In 1839, a single specimen of a cactus originating in South America was introduced in Australia, which until then did not exist in that continent, the prickly pear. This plant proliferated intensely and, in a short time, occupied land previously used for livestock. After numerous failed attempts to combat the plant, in 1925 a small butterfly was introduced to Australia whose larvae feed on the stem of the prickly pear. As a consequence, the plants were destroyed at almost the same rate as they had initially proliferated. With the help of the text, check the alternative (s) you consider correct.

1. By introducing strange species into natural ecosystems, man can alter their balance, even leading to the extinction of some species.
2. The rapid proliferation of prickly pear on the Australian continent was the result of the plant’s adaptation to local conditions and the absence of natural enemies.
3. In the text, there is an example of a competitive relationship.
4. Biological control may be more effective in pest control than the use of pesticides.

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Biological control consists of suppressing pests using natural enemies. It is widely used in the control of various diseases. Regarding this type of control, check the CORRECT item:

1. In biological control, only certain parasites can be used.
2. The parasites used in biological control are insects or other animals such as fish, which eliminate pests in a more or less violent way, by sucking the hemolymph from the pests or by consuming their tissues.
3. Artificial biological control occurs when there is human interference; in nature it is not always possible to obtain an abundance of biological enemies and this affects the effectiveness of control, requiring human intervention.
4. Pathogens are organisms like nematodes or fungi that live at the expense of the body of another insect, feeding on its tissues and causing death at the same time that they complete their life cycle.

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In general, the methods used to manage pests and diseases in the organic system can be summarized in three main points:
   1) increase in plant resistance (adequate management, adapted species and biofertilizers);
   2) biological control and use of pheromones;
   3) physical protection, repellents and curative treatments based on natural products.

Biological control is based mainly on:

1. use of repellents produced by pests;
2. use of natural enemies;
3. placement of natural barriers preventing the access of the pest to the crop;
4. organic planting in pest-free areas;
5. elimination of the pest in the conventional way before the start of cultivation

You remember that your rice paddy was showing a grasshopper infestation, right? Looking more closely at your plants, you realized that the damage caused was significant when the grasshopper population reached a density of 20 individuals per batch of rice. You noticed, however, that in the ecosystem where your plantation was located, there were also four other species of insects, in addition to the grasshopper that you were trying to control.

In order to understand the interaction between these species, you carry out an experiment: you collect some individuals from the grasshopper population and start four breeding indoors. Subsequently, it introduces in each creation one of the other species of insects. The results observed in each of these creations are shown in the graphs below.

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The graph below shows the populations of grasshopper (green) and insect species 1 (pink) as seen in creation 1. Based on this result, would you be able to explain what is the interaction between the two species in nature?

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The graph below shows the populations of grasshopper (green) and insect species 2 (pink) as seen in creation 2. Based on this result, would you be able to explain what is the interaction between the two species in nature?

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The graph below shows the populations of grasshopper (green) and insect species 3 (pink) as seen in creation 3. Based on this result, would you be able to explain what is the interaction between the two species in nature?

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The graph below shows the populations of grasshopper (green) and insect species 4 (pink) as seen in creation 4. Based on this result, would you be able to explain what is the interaction between the two species in nature?

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How can the results of the experiments be useful to agriculture?

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Indicate which species (s) can be used in the management of the grasshopper.

• Species 1
• Species 2
• Species 3
• Species 4
• None of the species

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Your neighbor, instead of trying the techniques of biological control, opted to apply a pesticide in the plantation to combat this “plague”. Altogether he made three applications of pesticides. The graph below shows the results obtained by him.

In the graphic above, each blue vertical line corresponds to a moment of pesticide application. Explain the observed differences (in relation to the response of the locust population) between the type of control adopted by your neighbor to what would be expected in the adoption of biological control.