Lesson Notes By Weeks and Term v4 - SHS 2
LIVING ORGANISMS
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LIVING ORGANISMS
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Subject: Biology
Class: SHS 2
Term: 2nd Term
Week: 10
Grade code: 2.3.1.LI.2
Strand code: 3
Sub-strand code: 1
Content standard code: 2.3.1.CS.1
Indicator code: 2.3.1.LI.2
Theme: DIVERSITY OF LIVING THINGS AND THEIR ENVIRONMENT
Subtheme: LIVING ORGANISMS
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Welcome, students! Today, we are exploring the fascinating and often unseen world of insects that live right here in our communities. While we might see a butterfly and admire its beauty, or shoo away a housefly without a second thought, these small creatures have a massive impact on our lives. They affect our food, our health, and our country's economy. From the maize in our storage barns to the cocoa that is a backbone of Ghana's wealth, insects play a crucial role. In this lesson, we will investigate the "double-edged sword" of four common insects—the grain weevil, butterfly, housefly, and honeybee—understanding how they can be both beneficial (helpful) and harmful (destructive).
A. What is "Economic Importance"?
In Biology, "economic importance" refers to the effect (either positive or negative) that an organism has on the well-being of humans, especially concerning our resources, money, health, and food supply. Beneficial (Positive) Importance: When an organism helps us. For example, by pollinating our crops (increasing food), producing valuable products (like honey), or decomposing waste. Harmful (Negative) Importance: When an organism harms us. For example, by destroying our food supplies, spreading diseases, or causing financial loss.
We will now examine four specific insects found in Ghana and analyse their economic importance. B. The Grain Weevil (*Sitophilus* species, e.g., Maize Weevil)
The grain weevil is a small beetle with a long snout (rostrum) that it uses to bore into grains. They are a major pest of stored cereals in Ghana. Harmful Effects (Primary Economic Impact): Destruction of Stored Grains: The adult female weevil bores a hole in a grain (like maize, rice, or sorghum), lays an egg inside, and seals the hole. The larva hatches inside, eats the starchy interior of the grain, and develops into an adult. This makes the grain hollow, light, and useless for food or planting. Reduction in Quality and Quantity: Infested grains lose weight and nutritional value. The presence of weevils, their waste (faeces), and dead bodies contaminates the entire stock, giving it a bad smell and taste. Economic Loss for Farmers: A farmer can lose up to 30-40% of their harvested grain in storage due to weevil infestation. This is a direct loss of income. Imagine a farmer in the Volta Region who harvests 50 bags of maize. If weevils destroy 30%, she loses 15 bags of maize and the money she would have made from selling them. Threat to National Food Security: Widespread post-harvest losses reduce the amount of food available in the country, which can lead to higher food prices for everyone. Beneficial Effects: The grain weevil has no known significant beneficial effects for humans. Control Methods: Proper Drying: Grains must be dried thoroughly before storage (below 13% moisture content). Weevils thrive in moist conditions. Good Storage Hygiene: Storehouses (silos, barns) should be cleaned properly to remove any leftover infested grains before a new harvest is stored. Traditional Methods: Many local farmers mix dried grains with ash or powdered neem leaves, which can deter weevils. Airtight Storage: Using hermetic bags (like PICS bags) that cut off the oxygen supply suffocates and kills the weevils. Chemical Control: Use of approved insecticides and fumigants by trained personnel. This should be a last resort due to health risks and potential for chemical resistance. C. The Butterfly (Order: Lepidoptera)