Design an investigation

Insecticide toxicity to honeybees

Units 2, 5 and 8
10 points
About 23 minutes

You can use a calculator on this question, just like on exam day.

You read about a real-world environmental situation with a described figure or model, then pick out the parts of a scientific investigation (hypothesis, variables, controls), explain the science behind it, and propose solutions to the problems it raises. On the exam: Question 1 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question and its sources

A new insecticide is being considered for use on fruit orchards. Before approving it, scientists tested how toxic it is to honeybees, which pollinate the orchards.

Study design

The scientists divided worker honeybees from one hive into six groups of 30 bees. Each bee in a group received a single dose of the insecticide, dissolved in a small drop of solvent and applied to its back. One group received a drop of solvent with no insecticide. All groups were kept in identical cages at 25 °C with sugar water. After 48 hours, the scientists counted the dead bees in each group.

Source: Hypothetical study design

Figure 1: Dose-response data (plotted as a dose-response curve)

Dose (micrograms per bee)	Dead bees after 48 hours (out of 30)	Mortality (%)
0	0	0
0.01	1	3
0.02	5	17
0.04	15	50
0.08	25	83
0.16	30	100

Source: Hypothetical data

Suggested time: 23 minutes

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Part (a)

1 point

Based on Figure 1, identify the LD50 of the insecticide for honeybees. Include units.

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Part (b)

1 point

Describe the relationship between dose and mortality shown in Figure 1.

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Part (c)

1 point

Identify the control group in this investigation.

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Part (d)

1 point

Explain why the scientists gave the solvent to the control group instead of leaving those bees untreated.

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Part (e)

1 point

Explain why the scientists used 30 bees in each group rather than one bee.

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Part (f)

1 point

A second insecticide has an LD50 of 0.60 micrograms per bee. Identify which insecticide is more toxic to honeybees, and justify your answer.

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Part (g)

1 point

The insecticide breaks down slowly and dissolves in fat. Explain why birds that eat insects could end up with higher concentrations of the insecticide in their bodies than the insects have.

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Part (h)

1 point

Describe one effect a decline in honeybee populations could have on the orchards.

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Part (i)

1 point

Propose one integrated pest management (IPM) practice the orchard growers could use to reduce their use of this insecticide.

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Part (j)

1 point

Describe one disadvantage of integrated pest management for the orchard growers.

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