Leafminer

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We used the leaf miner as an example of different methods of sampling. Leaf miners are small flies, moths or sawflies whose larvae burrow in between the two surfaces of a leaf. They can restrict the growth of plants and their health but they are not a massive threat to plants and if the plant is healthy enough to start with then it won't sustain too much damage. Many plants are susceptible to leaf miners including holly, cabbage, citrus trees and shrubs. In spring, as temperatures warm, larvae enter the pupal stage and then appear as young adults in April time. Females lay up to 250 eggs under the leaf epidermis and these eggs appear as raised spots on the leaf. After about 10 days the larvae hatch and tunnel through the mid tissue of the lead whilst feeding on the leaf. 
A leaf miner, Liriomyza brassicae, on a holly leaf. Photo: Olivia Davis
In order to estimate the population size of the holly leaf miner, which is what we were doing, the abundance of holly trees in the area was calculated by either counting every individual in the area or doing a random sample and extrapolating the data up. My group then counted the number of leaves on 30 branches of the holly tree each (there were 5 of us in the group so we had a total of 150 branches) and worked out the percentage of leaves on that branch that had leaf miners. We then compared this to the number of holly trees in the area and calculated an estimate of the holly leaf miner population in the area. This should have then been repeated every month or so to get a representation of the population.

This was a fairly hard survey to conduct as there was no way to count every single leaf miner unless all the trees were cut down and all leafs were individually observed. Considerations had to be taken into account to allow for these difficulties. The size of the sample needs to be large enough to increase the accuracy of the survey but time and cost evaluation also needs to be taken into account.

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