Southern armyworm feeding on soybean

Southern armyworm (Spodoptera eridania) late-instar larva feeding on soybean.

Southern armyworm (Spodoptera eridania) late-instar larva feeding on soybean.

Here is another animated gif that I made recently, this one showing a late-instar larva of southern armyworm (Spodoptera eridania) feeding on soybean (Glycine max). This polyphagous species is widely distributed from the southern U.S. through the northern half of South America and feeds on a variety of weeds, especially pigweed (Amaranthus spp.) and pokeweed (Phytolacca americana). It also occasionally attacks vegetable, fruit, and ornamental crops; however, in recent years it has become increasingly important on cultivated soybean in Brazil and Argentina, especially in regions where cotton is also cultivated. As a result, they have become one of the insects that I deal with regularly in my own research. More information on this and other armyworm species that affect soybean can be found in my earlier post, Quick Guide to Armyworms on Soybean.

Like many other lepidopteran caterpillars that feed on foliage, late-instar larvae become “feeding machines” that remain active both day and night as they try to cram as much nutrition into their expanding bag of a body as possible in preparation for an adult life focused solely on finding mates and laying eggs. Large larvae actively feeding during the day can be rather conspicuous, and as a result they often secrete themselves on the undersides of the leaves while feeding to make themselves less visible to predators. As they feed, however, a “window” opens up that gradually eliminates their cover. Rather than remaining in the same spot and feeding until they are completely exposed, however, larvae will move when the feeding hole reaches a certain size and find another place to conceal themselves before resuming feeding. Different caterpillar species have different exposure tolerances, and as a result, this combines with slight differences also in preferred tissue types to create recognizable differences in the damage patterns resulting from feeding by different species.

For those interested, making these animated gifs is really simple and allows those of us without expensive macro-video gear to simulate short videos of insect behavior. I make my animated gifs at—all you do is take a series of photos, touch them up in photo editing software (I use Photoshop Elements to adjust levels, color and sharpness), upload them to the site in the sequence desired, and click “Create Now”. It couldn’t be easier! You don’t even need a “real” camera—I took the photos for this gif with my iPhone using the “burst” function to take a rapid sequence of photos (all you do is hold your finger down on the shutter button for the desired length of time).

© Ted C. MacRae

4 thoughts on “Southern armyworm feeding on soybean

  1. Hi, Ted. I have found Hugin’s align_image_stack tool very useful in my photo-series-to-animated-GIF workflow. (You might know Hugin for its more popular use as a panorama stitcher.) It does a great job of stabilizing a series of images. Here’s an example:

    Squirrel Munching

    I’m not sure how it would fit in your workflow, but the basic usage looks like:

    align_image_stack -a output input1.jpg input2.jpg … inputN.jpg

    That gives you output1.tif, output2.tif, … outputN.tif, which you can convert back to JPEG and upload to GIFMaker, I presume. I use Gimp as a photo editor, so I just open the output files as layers and export that as an animated GIF.


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