Week Number of weevils per 100 g 1 4 2 12 3 25 4 48 5 85 6 142 (a) Table 1.1 shows the number of weevils found per 100 g sample of stored maize grain over a...
Question 1 Report
| Week | Number of weevils per 100 g |
|---|---|
| 1 | 4 |
| 2 | 12 |
| 3 | 25 |
| 4 | 48 |
| 5 | 85 |
| 6 | 142 |
(a) Table 1.1 shows the number of weevils found per 100 g sample of stored maize grain over a six-week period.
Table 1.1
(i) Describe the trend shown by the data in Table 1.1. [2]
(ii) Calculate the percentage increase in weevil numbers between week 2 and week 6. Show your working. [2]
(b) Suggest two methods the farmer could use to prevent weevil damage in stored grain. [2]
(c) Explain why pest damage in stored crops can have a greater economic impact than pest damage in the field. [2]
[Total: 8]
Answer Details
(a)(i) The data shows a continuous increase in the number of weevils per 100 g of stored maize over the six-week period, rising from 4 in week 1 to 142 in week 6. [1] The rate of increase accelerates in the later weeks: for example, the jump from week 5 to week 6 alone is 57 weevils, compared with only 8 between week 1 and week 2. This pattern is characteristic of exponential population growth, where each generation of weevils produces more offspring than the last because there are more breeding adults. [1]
(a)(ii) The percentage increase in weevil numbers between week 2 and week 6 is calculated as follows:
Increase = week 6 count - week 2 count = 142 - 12 = 130 [1]
Percentage increase = \(\frac{130}{12} \times 100 = 1083.3\%\) [1]
The original value (week 2) is used as the denominator because percentage increase is always calculated relative to the starting figure.
(b) Two methods to prevent weevil damage in stored grain (any two):
- Dry the grain thoroughly before storage to below 13% moisture content. Weevils need moisture to reproduce, so dry grain is a hostile environment for them. [1]
- Store grain in airtight (hermetic) containers or bags. This deprives weevils of oxygen, suffocating adults and preventing eggs from developing. [1]
Other acceptable methods: treating grain with an approved storage insecticide such as Actellic dust, or using traditional methods such as mixing grain with wood ash or neem leaves.
(c) Pest damage in stored crops has a greater economic impact than field damage because the crop has already absorbed all the costs of production: seed, land preparation, fertiliser, labour, weeding, and harvesting. [1] Losing stored grain means the farmer loses both the crop itself and every input cost invested in producing it. In contrast, a crop damaged in the field may partially recover through regrowth, and the farmer has not yet invested in harvesting and storage costs. [1]
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