Maple Leaf Miners, Canopy

by Carl Strang

On Saturday I returned to Maple Grove and Meacham Grove Forest Preserves to complete this year’s measurements of leaf miners in black and sugar maples. Earlier I reported the results for the understory. This time I was looking at fallen leaves to index leaf miner abundance in the forest as a whole. This can be regarded as a measure of these tiny caterpillars in the canopy, in part because the vast majority of leaves grow there and in part because saplings still are holding many of their leaves at this point in the season.

I went to 10 randomly selected points at each preserve and examined 30 leaves per point. The sunny, calm day was good for this as mines can be difficult to see after the fallen leaves have turned brown. I can hold the leaf so the sun shines on each surface, then hold it up so light shines through it.

In the five years that I have taken this measurement I have found few differences between canopy and understory leaf miner abundances. The most common difference is a lower incidence of Phyllonorycter tent mines in the canopy than in the understory, and such was the case this year at Maple Grove. Also at Maple Grove, Caloptilia boxfolds were less common in the canopy than in the understory this year.

All four genera of these tiny moths were in low numbers in the canopies of both preserves. The most abundant were Phyllonorycter at Maple Grove, where I found tent mines on 15 of 300 leaves, or 5%. That was the only species which produced a statistically significant difference between the preserves. In general, populations have been low since I began measuring canopy leaves, so I have yet to see a consistent pattern of differences. The only complete miss this year in understory and canopy combined was an absence of linear mines (probably produced by the non-native moth Stigmella aceris) at Meacham Grove (one turned up in the canopy sample there last year).

I have been interested in the effect of the more intensive management at Meacham Grove on insects and plants I am studying in these preserves. On Saturday I noticed that a burn had been attempted yet again at Meacham.

As you can see, the line of burning fuel dripped along the edge of the trail (which serves as a firebreak) did not take. There still is time for another attempt this fall.

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Maple Leaf Miners, Understory

by Carl Strang

In addition to the trailing strawberry bush (reviewed yesterday), I looked at leaf miners on understory sugar and black maples at Maple Grove and Meacham Grove forest preserves last week. As was the case with the other study, I was interested in the potential impact of controlled burning on the populations of the tiny moths whose caterpillars mine the leaves. Even after a year, the burned areas still had essentially no leaf litter.

Unburned areas at Maple Grove, and in a separate, off-study-area forest in Meacham Grove Forest Preserve, had plenty of litter remaining.

The upshot, though, is that I cannot identify any impact of that fire on leaf miner populations. This is not because they are all high, but rather because the four genera of miners have been consistently low at Meacham Grove for 15 years, now. This year, likewise, maple leaves were very clean at Meacham.

That result, I suspect, is more from the sustained intensive management at Meacham Grove over the years, with greater removal of understory maple saplings and more frequent and extensive burning. This is consistent with Meacham Grove’s forest having more of an oak component, a sign that it was exposed more to fire in its early days, fire that would have limited maple reproduction and dominance. The differences I have observed between the two forests in understory leaf miner populations thus may reflect a historically significant difference in the ecologies of the two preserves. Certainly the management at Meacham has produced an increase in botanical diversity of forest floor plants there.

In three of the four leaf miner genera, understory populations were higher this year at Maple Grove than at Meacham Grove. At Maple Grove, Caloptilia were present on 8% of understory leaves (2% at Meacham), probable Stigmella were on 3% (0% at Meacham), and Phyllonorycter were on a whopping 19% of understory leaves (0% at Meacham). The difference in Cameraria blotch mines, on 2% of Maple Grove leaves and 0% of Meacham Grove leaves, was not statistically significant (for more on these insects, go here). Though I did not take measurements, Phyllonorycter tent mines to the eye were much more abundant in the unburned, less managed forest block at Meacham Grove, and thus resembled Maple Grove.

At Maple Grove, two of the four insect groups increased over last year. That 19% figure for Phyllonorycter in fact is the highest since before 1996, and it is the fifth time that population has occurred on more than 10% of leaves in that period. The median annual value in those 15 years has been a healthy 6%. Caloptilia likewise have stayed strong, with a median matching this year’s value of 8%. This year’s frequency of 3% likewise is the median value for Maple Grove (probable) Stigmella. Cameraria has stayed low, with a median of 2% (also this year’s Maple Grove value). The respective medians for Meacham Grove have been 1%, 4%, 1%, and 0%. All of this discussion has been about the understory. The forest canopy may produce different results, which I’ll investigate in November.

Canopy Leaf Miners 2009

by Carl Strang

Recently I reported the results of my survey of black/sugar maple leaves in the forest understory at Maple Grove and Meacham Grove Forest Preserves. Each year I measure the incidence of four groups of leaf miners on those trees at those preserves, continuing a study I began in the 1980’s. Having found very few leaf miners of any type on the low saplings in September, I returned in November to gather data from fallen leaves, nearly all of which come from the canopies of mature trees.

Linear mine on a fallen leaf

As in the understory, canopy leaves had relatively few leaf miners. The highest incidence in any 300-leaf sample was 11 leaves bearing blotch mines of Cameraria caterpillars at Maple Grove. In comparisons between canopy and understory incidences, none were statistically significant. Comparisons between canopies of the two study areas likewise revealed no differences.

I also compared leaf miner incidences between 2009 and 2008. The only statistically significant changes were decreases in Caloptilia boxfolds at Maple Grove, both in the understory (a drop from 42 to 9) and in the canopy (a similar drop from 32 to 9).

It is worth noting that I found low numbers of all four mine types at both preserves this year.

Cameraria mine in a fallen leaf

This is the first time since 2006 that the sample included Cameraria at Meacham Grove.

Understory Leaf Miners 2009

by Carl Strang

In a series of posts last winter I outlined my results to date in a study of several species of leaf mining moth caterpillars that occur on black/sugar maples at Maple Grove and Meacham Grove Forest Preserves. This study, begun in the 1980’s, continues to be worth pursuing; I put in a total of about one full field day per year.

ACNI tent mine b

Tent mine formed by Phyllonorycter larva

One aspect of the study is a comparison of leaf miner occurrence in the canopy versus the understory. Today I’ll report this year’s results for the understory, having gathered those data in September. The story can be told simply, as I found very few leaf miners of any kind at either study area. Out of the 300-leaf samples from each preserve, the greatest number of leaves bearing a leaf mine type was 9 (Caloptilia boxfolds at Maple Grove). That number itself represented the only statistically significant change from 2008, having dropped from 42 leaves in last year’s Maple Grove sample. In comparisons between study areas, only the linear mines which I believe are produced by Stigmella showed a difference. Technically, however, the 8 leaves at Maple Grove versus 0 leaves at Meacham do not meet the criteria for the statistical test I use.

Maple leaves 19SEb

So in the understory the maple leaves were about as clean as I have ever found them. I’ll go out to collect the canopy data soon.

Leaf Miners 3

by Carl Strang

 

A few weeks ago I introduced my ongoing study of leaf miners in maple leaves, moths so tiny that their caterpillars live between the upper and lower surfaces of leaves. I left a few questions unanswered, and I want to return to what I have learned so far in attempting to answer them.

 

Cameraria saccharella adult specimen

Cameraria saccharella adult specimen

 

 

  • These two study areas are separated by many miles of suburbs. Do the populations of the leaf mining species go up and down together on the different study areas (which might reflect responses to climate as it varies between years), or do they fluctuate independently (which might indicate biological regulation of populations)?

 

Numbers of these insects have been so low since my return to this study in 1996 that drawing conclusions is problematic. However, there have been several occasions when proportions of leaves with one type of mine have been significantly higher on one preserve than the other. In the case of the boxfold species, Caloptilia, there were appreciably more at Meacham Grove in 1996, and at Maple Grove in 2004 and 2008. The tent-mine-forming Phyllonorycter has consistently been more abundant in Maple Grove samples over the years, and this difference has been statistically significant several times. Other miners have been present at such low levels that for all practical purposes they have been the same.

 

  • How does restoration management practice affect these organisms? These maples are the main target of management in these forests, because they are so shade tolerant that they can push out all the other plant species over time. Once they were kept in check by the rare fires that reached even the moister woodlands. Now, selective removal of maple saplings and controlled burns are used to restore higher diversities of other plants, of the many insects that depend on those plants, and the consumers of those insects.

 

The potential impact of management on these leaf miners has to be speculative, as little is known about their natural history. Meacham Grove has been managed more intensively than Maple Grove, though both preserves have received some attention. Is this why Phyllonorycter has remained so low in numbers at Meacham? Though the differences are not statistically significant, in almost every year the numbers are slightly smaller at Meacham than at Maple Grove for Cameraria blotch mines and (presumed) Stigmella linear mines, too.

 

A controlled burn of the leaf litter at Meacham Grove in the fall of 2007 was followed by practically no leaf miners of any kind in understory maples in 2008, but their numbers were so low in 2007 that any connection to the burn would be hard to argue. If the moths overwinter in that litter, the burn may have knocked them down enough that I may see very low numbers there for several years.

 

  • Do the moths have the same impact on the canopies of large trees as they have in the understory?

 

All of my 1980’s focus was on saplings in the understory. In recent years I have attempted to compare the understory and canopy trees, first by looking at leaves on the branches of large trees that could be reached from the ground, and second by measuring incidence of mines on fallen leaves (the vast majority of which come from the canopies of the larger trees; also, the larger trees lose most of their leaves before the saplings do, so I can improve the distinction with careful timing).

 

In 2005 I looked at leaves on low branches of larger trees, and found no difference in any of the leaf miners from what I measured in understory plants. This is not necessarily a trivial comparison; large trees have greater resources with which to create chemical or physical defenses, and might have had fewer miners.

 

In 2006-8 I have been looking at fallen leaves as a measure of leaf miners throughout the forest. After three years I have only tentative conclusions. It is beginning to appear that tent-mining Phyllonorycter prefers the understory, supporting the possibility that management removal of maple saplings has had an impact on that species at Meacham Grove (some do live in the larger trees, however, and the number of leaves in those trees is so huge that a 1% incidence level still represents a lot of moths). The other miners have not shown differences between canopy and understory, though it should be said that blotch-mining Cameraria and linear-mining presumed Stigmella are at such low levels at Meacham Grove that nothing really can be said about them from these few years.

Do the Leaf Miners Avoid One Another?

By Carl Strang

 

Yesterday I described several species of tiny moths whose caterpillars mine the leaves of black/sugar maples in DuPage County, Illinois. Today I want to review some of the results of my inquiries into this system (by “system” I mean a group of interacting species in a particular environment) since 1983.

 

In the mid-1980’s these species all were abundant, and collectively they were removing a significant portion (in 1984 more than 20%) of the maples’ photosynthetic tissue in understory plants. We might expect that in such a situation it might benefit them to avoid one another. There are mathematical methods, called statistical tests, that allow us to say whether the co-occurrence of these herbivores on leaves is taking place randomly (no interaction evident), whether they may be avoiding one another (co-ocurrence on leaves is less than one would find in a random situation), or whether they are attracted to one another or at least to the same leaves (co-occurrence greater than in the random case).

 

acer-leaf-miners-b

 

I made these comparisons in 1984, 1985, and 1986. If there are any interactions between these leaf miner species, we would expect to see the same result showing that to be the case in each year. With four mine types, there are 6 ways any two of them can form a pair for comparison in a given year. That makes 18 statistical tests over the three years. Out of these 18, only four showed a statistically significant departure from random co-occurrence. However, only two of the four involved the same two species, Caloptilia and presumed Stigmella in 1985 and 1986. Those same two species gave a random result, however, in 1984, the year when leaf tissue loss was highest and presumably there would be the greatest benefit from avoidance. On the whole I had to conclude that these species are interacting weakly if at all.

 

This seems puzzling, but I have a guess as to why it’s the case. When I returned to this system in 1996 I found the populations of leaf miners very low compared to the 1980’s. Only in the case of Caloptilia at Meacham Grove did more than 10% of the leaves have one or more of these insects. Populations have remained at or below these levels ever since. It’s beginning to look like the high numbers of the mid-1980’s were unusual, so that there has not been selective pressure to benefit individuals with avoidance behavior.

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