Insect structures: what's in the bag?

Insect structures: what’s in the bag?
The purpose of this week’s lab was to be able to sort through samples from sorghum and soybean fields in the area and sort out the insects. We had to sort the insects by mouth parts because mouthparts are a main diagnostic key when identifying insect pest damage.

The first bag I sorted was sampled from soybean field in Manhattan, KS. In this bag I sorted out 27 insects; 88% of the insects had chewing mouth parts, 7% had piercing-sucking mouth parts, and 3% had siphoning mouth parts. The piecing-sucking insects were both stinkbugs, and the insect with siphoning mouth parts was a moth. The insects with chewing mouth parts were broken down into the following groups: 58% green beetle, 17% caterpillars, 17% green field crickets, and 8% green lacewing. The orders in the soybean field were: Lepidoptera, Hemiptera: Pentatomidae, Coleoptera, and Neuroptera: Chrysopidae, and Orthoptera: Gryllidae.

The second bag I sorted through was sampled from a sorghum field in Manhattan, KS. This bag had 20 insects; 90% had chewing mouth parts and 10% had piercing-sucking mouth parts. Again the piecing sucking insects were green stinkbugs. As for the insects with chewing mouth parts 78% of the insects were caterpillars, 11% were green beetles, 5% were green field crickets, and 5% were green lacewings. The orders in the soybean field were the same as the orders in the soybean field.

After the insects were sorted through I picked a green lacewing from the soybean field to look at under the Dino-Lite microscope. I picked this insect because I knew it was a beneficial insect; however, I have never taken the time to really look at it up close. Green lacewings belong to the order Neuroptera and family Chrysopidae. The larvae are typically predaceous and feed on aphids, while the adults may be predaceous, feed on pollen, or feed on honeydew. The eggs are laid on a thin stalk, with the the egg attached to the end. The larvae pupate in cocoons attached to the underside of leaves, and adults overwinter in the forest (Triplehorn and Johnson 2005). The picture below shows the green lacewing’s external anatomy. Green lacewings have a prognathous head orientation, with filiform (thread-like) antennae. These insects move around with their wings, and legs.

There were a couple of difficult parts in the lab for me. The first difficulty came when sorting. There were not enough forceps for the whole class so we had to use big green plastic ones. This made it difficult to grab the insects without smashing them. Another difficulty was with the microscope. It took a good picture, but I didn’t know I could get closer to it. For instance, I would have liked to zoom in so that I could have gotten a better view of the chewing mouth parts. This picture does not make it easy to distinguish individual mouth structures. The third difficulty was realizing that I didn’t know anything about insect larvae! I’m looking forward to being able to identify all the insect larvae that were in the bag.

Using this type of identification method in the field would be difficult. You would need to set up the computer and microscope, which depending on where you are may be an issue. Another difficulty of using this method in the field would be that it would be hard to observe the insect under the microscope if it was still alive. I would suggest bringing a kill jar out to the field with you so you don’t have to worry about the insect flying or crawling away.