Aphididae

“The Botanists Among Us: Host plant specialization in insects”

/ Ted C. MacRae / 4 Comments

It’s been a busy week for me—just two days after doing a presentation on tiger beetles to the Webster Groves Nature Society’s Entomology Group, I gave a talk to the St. Louis Chapter of the Missouri Native Plant Society. As implied by the title, the talk focused on host plant specialization among insects, first covering the major groups of plant-feeding insects and the evolutionary themes involved in adaption to (and away from) plant-feeding, then moving to examples of different types of host plant specificity and highlighting some of the more interesting insects that I’ve encountered (and managed to photograph) over the years.

Like my talk two nights earlier, it was another fun and lighthearted conversation with a highly engaged crowd, and I appreciate the great interest shown by a group that is normally much more focused on plants than on insects. Once again, it was well-attended locally, but for the benefit of those who were not able to attend the meeting in person and that may be interested in this subject, I’ve prepared a PDF version* of the presentation that you can download and peruse at your convenience.

* All content is copyrighted and may not be reproduced or distributed without written consent.

© Ted C. MacRae 2019

Life at 8X: MPMI Cover

/ Ted C. MacRae / 2 Comments


The January 2013 issue of Molecular Plant-Microbe Interactions (volume 26, number 1) is now online. Why do I mention this? You may recall the cover photos of the soybean aphid, Aphis glycines, from my post —one of a series of posts I’ve done featuring insects photographed at 8X life-size.

MPMI is a publication of The American Phytopathological Society, and I have Dr. Gustavo MacIntosh at Iowa State University to thank for the appearance of these photos on the cover of this Special Focus Issue. Dr. MacIntosh is Associate Professor of Biochemistry, Biophysics and Molecular Biology and studies hormone-based defense mechanisms in soybeans. In a paper appearing in this special issue, Dr. MacIntosh and co-author Matthew Studham published the results of a study that suggests soybean aphids are able to “short-circuit” soybean defense mechanisms, making it easier for other pests (e.g., soybean cyst nematode) to colonize infested plants as well. Their study revealed large differences in transcription profiles of soybean varieties with and without an endogenous resistance gene (Rag1) in response to aphid infestation and suggested that the aphids are able to circumvent the defense response in susceptible plants by triggering activation of abscissic acid (normally associated with abiotic stress responses) as a “decoy” strategy (Studham & MacIntosh 2013). Plants infested with aphids have been shown to also become more susceptible to soybean cyst nematode—even varieties with genetic resistance to nematodes (McCarville et al. 2012). Dr. MacIntosh saw my photos when I posted them here and asked permission to submit them as candidates for the cover of the MPMI issue in which his paper was to appear.

Dr. Macintosh hopes that his research will enable the development of soybean varieties that will be more resistant to aphids and other pests.

REFERENCE:

McCarville, M. T., M. O’Neal, G. L. Tylka, C. Kanobe & G. C. MacIntosh. 2012. A nematode, fungus, and aphid interact via a shared host plant: implications for soybean management. Entomologia Experimentalis et Applicata 143(1):55–66 [DOI: 10.1111/j.1570-7458.2012.01227.x].

Studham, M. E. & G. C. MacIntosh. 2013. Multiple Phytohormone Signals Control the Transcriptional Response to Soybean Aphid Infestation in Susceptible and Resistant Soybean Plants. Molecular Plant-Microbe Interactions 26(1):116–129 [DOI: 10.1094/MPMI-05-12-0124-FI].

Copyright © Ted C. MacRae 2012

Life at 8X—soybean aphid

/ Ted C. MacRae / 12 Comments

Although my first attempt at adding extension tubes to my Canon MP-E 65mm macro lens, effectively converting it from a 1–5X to a 1.7–8.0X lens, was nearly a year ago, it has only been recently that I’ve actually started experimenting with this combination to obtain high-mag photographs of very small insects in the field. The first example that I showed of such a photograph was a tiny seed weevil (Althaeus sp.) on its hibiscus host plant. I’ve since photographed a number of other insect subjects at high-mag using this setup and am getting a better feel for the capabilities—and limitations—inherent in using it. First, here is what the setup actually looks like:

Canon 50D body, MP-E 65mm macro lens on 68mm extension, MT-24EX twin flash w/ DIY diffuser.

Not the normal photo quality for this site (just a quick field setup photographed with my I-Phone), but it shows just how long the lens component becomes when fully extended to achieve 8X magnification. The camera is quite front-heavy, making the camera difficult to use hand-held, and the very shallow DOF (depth of field) due to the extreme level of magnification makes precise focusing difficult and magnifies the effect of any motion between the camera and subject. Obviously, one solution for these problems is to mount the camera on a tripod and place the subject on a stable surface; however, for reasons I’ve mentioned elsewhere, it is unlikely that I will ever take to bringing a tripod into the field, and the whole point of this exercise is to develop the capability for getting usable hand-held field photographs no matter what level of magnification they may require. As an alternative, I use a number of other techniques, discussed in my prior post on the subject, to stabilize the camera without using a tripod.

One of the recent subjects I photographed with this setup is the soybean aphid, Aphis glycines (order Hemiptera, family Aphididae). This distinctive Asian species has recently established in the U.S. as invasive pest of soybeans; adult females measure only 1–2 mm in length (and the nymphs are even smaller) and can quickly develop very high densities on the leaves and upper stems of soybean plants. The following photograph was taken at the camera setup’s minimum magnification of 1.7X and provides a typical view of adult aphids and their progeny:

Aphis glycines (soybean aphid) | Warren Co., Illinois

While the above photograph does a very good job of showing the colonial appearance of infestations by these aphids on soybean foliage, what about the aphids themselves? It would be nice to get a better look at individual aphids. The following photographs were all taken with the lens fully extended to achieve 8X magnification (and completely hand-held):

Adult female aphid—note the eye spots of the unborn nymphs visible within the body.

Another adult female navigates the hairs on the surface of the soybean leaf (I never knew soybean leaves were so hairy!).

A mother surrounded by her progeny. As above, eye spots of unborn nymphs can be seen inside her body.

These photographs are not without their problems—they are a bit soft, probably due to motion blur that results from the camera being hand-held and the extremely thin DOF that makes it difficult to get all of the desired components of the photos equally in focus. Lighting also is a challenge, as the very small subject-to-lens distance forces light from the flash to come from directly above or even behind the subject while minimizing front lighting (especially evident in the last photo with its straight down view). Nevertheless, these are decent, usable photographs that provide an uncommon view of these exceedingly tiny insects—without the encumbrance of carrying a tripod in the field, the time investment of studio photography and/or focus-stacking, or the expense of a microscope-mounted camera system (for those of us without access to such systems).

Copyright © Ted C. MacRae 2012

Pickle Springs Natural Area

/ Ted C. MacRae / 3 Comments

Pickle Springs Natural Area lies in Ste. Genevieve County, about an hour south of St. Louis. Like Hawn State Park, the geology of this area and its effect on the flora have resulted in a unique collection of geologic features and plants found in few other places. The Lamotte sandstone outcrops that dot the landscape were formed nearly half a billion years ago when sand deposited in an extensive maze of braided river channels was cemented and buried under younger layers of limestone and dolomite formed from deposits on the floors of ancient seas that covered the interior of the continent. Later, the periods of uplift that created the St. Francois Mountains and resulting erosion of overlying strata once again exposed the sandstones at the surface. Millions of years of water, ice, rain, wind, and plants have further shaped the exposed sandstones, creating fanstastic shapes and formations and cool, deep canyons. The weathered sandstone created acid soils which support many unique plants. During the ice ages, northern plants and animals moved into the area ahead of the advancing glaciers. Mammoths roamed the landscape grazing on the northern vegetation supported by the area’s acid soils. Eventually the ice retreated, and so did the mammoths. But many of the plants remained – able to hang on in the cool, moist canyons long after the mammoths that once roamed these canyons disappeared. Because of this unique concentration of rare plants and geologic features, the area has been designated a Missouri Natural Area and a National Natural Landmark.

Yesterday I hiked the aptly-named ‘Trail Through Time’ with my family. This 2-mile trail is one of the most “feature-packed” trails in the state, with something to look at around almost every bend. Almost immediately the trail leads to the Slot, the result of a vertical fracture in the Lamotte sandstone that was loosened by leaching and then widened by erosion. The unique partridge berry (Mitchella repens) was seen on the moist, vertical walls of the rock, growing among strange holes, pockets, and ridges that formed as a result of the sand grains being variably cemented.


A short distance from The Slot lie Cauliflower Rocks – large moundlike formations (also called hoodoos or rock pillars) formed from jointed or fractured sandstone that undergoes deep solutional weathering followed by erosion and weather-mediated shaping. Hoodoos occur primarily in this type of rock due to its granular, variably cemented and cross-bedded matrix.


On the south side of Cauliflower Rocks lies a special type of buttress arch called Double Arch. It occurs at almost a right angle to the adjacent rock outrcrops, suggesting formation along a set of fractures running perpendicular to the main fracture trend of the area, but the precise details of its formation remain a mystery.


After leaving Cauliflower Rocks the trail descends steeply into a deep valley, at the bottom of which lies Pickle Creek just below its origin in a box canyon south of the Natural Area. Lush vegetation in this cool, moist valley contrasts with the stark rocks seen earlier.


The creek is fed by a series of seeps, allowing the valley to remain moist even during the dry summer months, and along with the acid soils support a unique plant community. Lush colonies of ferns (I believe this is Polypodium virginianum L.) covered the rocks adjacent to the creek…


…while this rattlesnake plantain orchid (Goodyera pubescens) was seen in a colony growing at the base of a black oak tree (Quercus velutina) just above the creek.


Mosses and lichens were also abundant in the valley. This little hair cap moss (Polytrichum sp.) with its distinctive fruiting structures was growing in a colony at the base of another black oak tree. The members of this genus prefer acidic environments.


Further ahead, along Bone Creek, several colonies of wooly aphids (family Aphididae) were seen on the branches of a small hop hornbeam tree (Ostrya virginiana).


The highlight of the hike had to be in Spirit Canyon at Owl’s Den Bluff. The horizontal layers of sandstone, each deposited on the steep downstream slopes of sandbars, are clearly visible in the towering bluff face. At the bottom lie bluff shelters – formed where lower sandstone layers collapse due to weathering or leaching, and where native Americans almost surely camped out. The sun never reaches parts of these shelters, providing ideal conditions for a variety of mosses and liverworts – many of which are known only from this area. Fallen boulders and collapsed portions of the bluff face provided photo opps for the daring…


…and good exploring for the nimble.


By now, the trail has passed the halfway point and is looping back to the west, where it ascends to Dome Rock Overlook. Along the way, a fascinating variety of lichens, including reindeer lichen, covers the forest floor where they are supported by the acid soils.


Dome Rock Overlook is a the largest hoodoo complex in the Natural Area. The thin soils and exposed conditions create a harsh, dry, windswept environment that only the hardiest of plants can withstand. Only a few small blackjack oaks (Quercus marilandica), shortleaf pines (Pinus echinata), and farkleberry (Vaccinium arboreum) survive here. Despite their small size, some of the trees growing here are at least 150 years old.


The trail descends from Dome Rock Overlook and passes underneath, providing spectacular views of the sheer rock face below the overlook. The trail completes its descent back into Pickle Creek Valley, where Pickle Spring can be seen. This small, permanent spring – an unusual feature in sandstone where seeps are more common – was an important source of water for early settlers.


Further along the trail lies one of the areas most unusual features – Rockpile Canyon – formed some 50 years ago (a fraction of a second in geologic time) when part of a sandstone bluff collapsed in a rumble, leaving behind a sheer bluff face and a jumbled pile of large boulders. A short spur in the trail leads to the head of a small box canyon, where some of the 20+ ice age relict plant species can be seen growing in the acid soils and cool, moist canyon walls.

Near the end of the loop lies Piney Glade, an area where the exposed sandstone bedrock once again creates a dry, harsh environment. Poverty grass and little bluestem grow in small, shallow pockets of soil scattered amongst stunted shortleaf pines and blackjack oaks – creating a small prairie surrounded by a sea of forest. All three forms of lichens can be found on the rocks and soils of the glade – the aptly named crustose lichens cling tightly to rock surfaces amongst foliose (leafy) and fruticose (branched) lichens.