RESULTS: We found that in 61% of the leaves examined, the larvae mining was mostly concentrated along the edges of the leaf. Mining patterns would often trace the circumference of a leaf, as shown in Figure 1. below.
On the other hand, the mining patterns did not show a significant preference for certain parts of the leaf aside from the edge. Of the mens cologne catalogued in this study, 47% exhibited mining trails spread across the entire length of the leaf, and 50% had trails which crossed the center vein existing on both the left and right side of the hugo boss fragrance.
Figure 2. above shows an edge preference in the base and all over trail locations. The category of mining patterns all over the length of the leaf with a edge preference is more than twice that of any other category.
Overall, we found that leafminer larvae in the plants we examined have a definite preference for mining the edges of leaves, but no obvious preference for any other particular spatial distribution. The only section of the leaf where no preference to the edge was higher than edge preference was the center section. Stiling, Simberloff and Anderson (1987), in their examination of leafminer patterns in oak leaves in Florida, found that larvae mines concentrated on one side of a leaf did not show any higher or lower correlation with most common larva mortality factors, including predation, competition, and parasitism. The conclusions from this study would help explain the lack of preference we observed for position preference – there does not appear to be an evolutionary advantage for the larvae to concentrate on one, the other, or both sides of the center vein of a leaf.
In addition, Dale (1992), in his in-depth analysis of the mechanics of leaf growth, proposes that the tip of a leaf actually includes the oldest cell tissue in most dicotyledon species, proving our initial assumption of an abundance of nutrient-rich young cells in the leaf tip incorrect. This finding helps to explain why mining larvae showed no distinct preference for the tip as opposed to other areas of the leaf.
The commonalities between mining patterns could additionally signify information about the species of larvae mining a given leaf sample. The Lopez-Vaamonde, Charles, Godfray and Cook (2003) study of the relationship between a leaf-mining moth species with their host plants concludes that the taxonomically related mining species seek taxonomically related host-plants despite a lack of evidence indicating any cospeciation. The evidence showed that geographic restriction can facilitate this specialized plant-larvae relationship, the species we found in the cloud forest grew in a habitat with very high moisture, high elevation, high disturbance (along hiking trails) and low light. Considering the distinct possibility that the mining insects feeding on the samples we took were of the same family the edge preference may be a result of common dietary patterns.
Additionally in a study of the Allograpta centropogonis by Nishida, Rothery and Thompson (2002) showed that the larvae feed gregariously, moving shoulder to shoulder, through the mines. The flower fly, native to Costa Rica, was observed to begin mining at the tip of the leaf and move toward the base, most often moving to a new leaf before consuming the first host leaf in it’s entirety. This would explain why we found similar mining trails on multiple leaves of one plant, moving from the highest leaf to lower ones. Clusters of eggs are laid on the outer margins of the leaf between the veins, and mining larvae begin their mines adjacent to where they hatched, moving toward the center vein. There was evidence found that the entry hole sometimes also serves as the exit hole, which would explain why the trails would be concentrated in one area, due to the larvae retracing their previous trail back to exit from their point of origin.
We sought to use observed patterns in insect larvae leaf mining to derive conclusions about the insects’ behavior, preferences, and morphology. While our data analysis remains cursory and our sample size is yet too small to draw any significant conclusions about the larvae from our observations, we did make observations that we hope will aid future studies and analysis. Overall, our observations and analysis concluded that larvae mining similar understory leaves in the Monteverde Cloud Forest Reserve overwhelmingly prefer to mine the edges of leaves, but exhibit no significant preference for the left or right side of the center vein versus both sides of the vein, nor do they exhibit a vertical mining preference for the tip, center, or base of the leaf. It remains a possibility that larvae prefer leaf edges because of greater nutrient concentration there, and the edge preference displayed by the leaf miner larvae could also indicate that the many of the larvae species surveyed were the same or similar type of insect exhibiting similar behavioral patterns.