Sampling leaf-miners on European Holly bushes

Friday 17th March 2017:
In order to put into practice the skills we have learnt as ecologists, in sampling species and estimating the total numbers of species in a given area, we were given the task of sampling leaf-miners on the leaves of Holly bushes (IIex aquifolium). Leaf-miners are the larvae of an insect that burrows into leaves and lives within them, and they eats the leaf tissue as they grow and develop. Leaf-mining insects include species from Lepidoptera, Symphyta and Diptera, amongst others.

Leaf-miners are seen as pests by agriculturalists and farmers, as they can cause significant damage to crops and plants, and reduce economic potential of a crop, producing difficulties for the farmer. They can be very hard to control using chemical pesticides as the larvae live within the leaf, not on it. A better method to control leaf-miner outbreaks, is to use "companion-planting", whereby a farmer may plant a nearby field or patch of ground with a distraction crop; one which distracts the leaf-miners and encourages them to eat this plant, as opposed to the actual crop plants the farmer cultivates for profit.

In sampling leaf-miners in holly bush leaves, we divided ourselves into groups, and my group was comprised of five individuals. We decided that the most efficient way to sample leaves on Holly bushes with leaf-miners, was to divide ourselves between 5 separate patches of woodland, and devise an easy and repeatable sampling method. So, each of us chose an area of 5-paces by 5-paces (roughly 25m^2).
Next, we made sure to sample at least 50 different sites on Holly bushes that fell within the boundaries of our sections of woodland. In doing this, we would find a branch that was high (roughly just above head-height), then a branch that was mid-height (roughly waist height), and finally a branch that was low (about 30cm off the ground), and we then found the stretches of new growth on each branch.
On each area of new growth, we recorded the number of leaves and then the number of leaves with leaf-miners. This figure could then be converted to a percentage of the total number of new leaves infected by leaf-miners.
We repeated this procedure for sampling leaf-miners in leaves at different points around each Holly bush in our areas, to retrieve as much data as possible.

In order to reduce the effects of anomalies or type 1 error (false positive), we took as many samples as possible. In addition to this, to reduce the likelihood of leaf-mines being re-recorded in future years/surveys, we only counted leaves in areas of new growth on each branch.

Our results suggested a great variation in the numbers of leaves at different heights on the holly bushes, and with this, a great variation in the numbers of leaf-mines recorded with height and number of leaves.

Leaf-miners in a Holly leaf (taken 23/03/17)