NC State University Insect Museum

(written by Ann Carr)

Today we had our last seminar session, and I have to say that most of us were sad to see it end. This has been an amazing class and one of the better seminars offered. We sure hope all of you bug enthusiasts have enjoyed following our discussions! We have learned some much, and hope that you learned a little too. Last weeks seminar topic was insect products with a focus on galls. We had a full house this week, so lucky for you there are quite a few papers to go over. So let’s get started! PS need to give a big “Thank You!” to Trish and Steve for making some amazing curry and banana pudding, which might I add pair together very well.

Insect morphology now infiltrates every aspect of our lives. Here, a wasp-inspired cookie crumb garnish adorns a delicious banana pudding. Yummy and educational!

Keith got us started with a paper discussing the phylogeny of the galling aphid species Eriosomatini. This paper suggests that the evolution of galling aphid species is largely affected by the presence of host plant species. Species divergence is closely associated with host plant extinction and subsequent diversification of host plant types. This theory makes sense because of the critical association galling aphids have with their host plants. By comparing insect and gall morphological features the authors are able to construct a very nice evolutionary tree and identify Eriosomatini’s closest sister species.

I followed with a paper examining survival strategies of Contarinia galling midges. Because the midges are most susceptible to mortality when they are in gall-forming phase, they have evolved long diapause periods in the soil. Contarinia midges have 99% of their population laying dormant in the soil. Their diapause periods last 10-17 years depending on emergence. This allows the species to survive extinction if all of their galling populations are exterminated. The authors also believe that because of the limited availability of their host plant, that the Contarinia midges must establish a long-lived population to evade extinction.

Matt talked about a paper that examined what happens when galls are on leaves that are aborted by the host tree. The authors compared two gall structures, simple and complex. They were able to conclude that the more complicated gall structures were able to survive on the forest floor once aborted by the host tree, unlike the simple gall structures. This was described as the “Green Island Effect” where the exterior tissues of the leaf died, though the tissue surrounding the complex gall remained green and viable for a period of time after falling from the host tree.

Trish found a paper that studied sexually dimorphic galls of scale insects. In the genus Apiomorpha females produce round circular galls and males produce long tubular galls. They were also interested in why two populations of the same species produced different galls. The authors did studies to see if the two populations were making different galls because of the host plants they were using. They concluded that the insect determines the gall shape, not the host plant, and during their research they discovered genetic variances between these two populations and re-established them as two separate species.

Andrew discussed a paper that examined why caddisfly larvae line their cases with pine needles. The caddisfly were not using the pine needles for camouflage or defense, but were actually using the pine needles to help anchor and stabilize themselves when confronted with strong or turbulent water currents. The authors note that caddisfly without pine needles would spin and rotate more than caddisfly with pine needles attached to their case.

Steve followed with a paper that talked about silk production in male dance flies. Dance flies are the first type of fly found to produce silk. Structurally their silk looks very similar to silk produced by Lepidopterans. Though, genetic analysis showed there were no similarities in composition between the dance fly silk and other insect silk products. This means that this is an entirely different silk from what is typically found. What was really neat was the purpose of the silk. Male dance flies would skim the surface or water sources and use the silk as a net to collect diatoms, and present the package as a nuptial gift to females.

Colin presented our last paper of the semester, which actually was a review on lac insects and the harvesting of shellac. Lac insects feed on the sap of trees and produce shellac while laying eggs. The shellec is scraped of the trees, harvested and finished all by hand. Variations in shellac are dependent on lac insect species. The paper also discussed the lac agriculture in India and Thailand, cultural demands, and threats to shellac harvesting.

Well that about sums it up for today. Thanks for following along. We hoped you enjoyed it as much as we did!

This week in Insect Morphology Seminar, we discussed several interesting papers about female genitalia and the insect ovipositor!

Steve started by telling us about germline stem cells (GSCs) in the ovaries of an earwig, Opisthocosmia silvestris. Studies in various animal species have shown that stem cells function in specialized microenvironments known as niches. Insect ovaries consist of ovarioles, which consist of the terminal filament, germarium and vitellarium. The morphology of the Drosophila GSC niche in females is known to house three types of somatic cells: terminal filament cells, cap cells, and escort stem cells. In C. elegans, the GSC niche only contains a distal tip cell equipped with long cytoplasmic structures. The female earwig GSCs are morphologically simple and consist of the terminal filament cells and escort cells; cap cells are absent and escort stem cells are not recognizable (see image below for a comparison of the three organisms).

Structure of the GSC niches in Caenorhabditis elegans, Opisthocosmia silvestris, and Drosophila melanogaster

Heather talked about how female cockroaches exchange water with their oothecae. German cockroaches usually carry their oothecae until the eggs are ready to hatch, and the success of embryogenesis may depend on water-balance between the adult female and the developing ootheca. Since oothecae that are detached from the female before embryogenesis is complete often cannot develop (especially in dry environments!), this led scientists to wonder how water is transferred to the ootheca during development. There is an area located on the proximal end of the ootheca that contains small pores that penetrate the escutcheon region of the covering of the ootheca to access the chorion! This may help maintain water balance between female and ootheca, and the German cockroach may represent an important evolutionary link in the transition from oviparity to ovoviviparity!

Colin discussed a very interesting paper on cryptic female choice in spiders and complex genital structures. Female haplogyne spiders of the species Opopaea fosuma have evolved some neat ways to get rid of or block sperm from males they have mated with. Female spiders have the anterior wall of the spermatheca, where sperm is stored before fertilization, heavily sclerotized with a cone-shaped hole in the upper part. Muscles attach to a transverse sclerite that bears a nail-like structure, and when the muscles contract, they press the nail into the hole of the spermatheca. When this happens, the copulatory orifice is enlarged and the resulting suction probably allows deposited sperm to be emptied from the spermatheca (called “sperm dumping”). This mechanism is commonly used among females to influence a male’s chance of fathering their offspring; this is known as cryptic female choice. So what makes the females decide they don’t like a particular male’s sperm? Is he just not up to her standards?

Keith and Andrew both talked about genetic patterning in genitalia of the milkweed bug Oncopeltus fasciatus and the red flour beetle Tribolium castaneum. These two species differ in the anatomical complexity of their genitalia. Researchers found that the posterior Hox genes (abdominal-A and Abdominal-B) were required for proper genital development in O. fasciatus and they regulated Distal-less and homothorax in a similar way in both sexes. They did RNAi knockdown experiments to look at genitalia development and found that the genitalia are not homologous to appendages in Tribolium but they are Oncopeltus. Andrew found a paper that discovered that the same genes that regulate genitalia development also regulate the development of beetle horns. The results provided developmental genetic support for specific anatomical hypotheses of serial homology. The gene functions and interactions describe the developmental patterning of sexually dimorphic structures such as genitalia that have been critical to the diversification of species-rich insect groups.

Matt finished up with a paper talking about mating plugs in scorpions. There are two kinds of plugs in scorpions, sclerotized and unsclerotized (gel-like), which usually harden in the female genital tract. The researchers found a gelatinous mating plug in Euscorpius italicus that is composed largely of sperm – this was previously unknown in arachnids! It was discovered that fluid from the female genital tract causes sperm activation.

Heather gave a great mini-lecture on wax production and insect products. The lecture began with galls – there are over 13,000 species of insects that produce galls, from sawflies to cynipid wasps to adelgids and many flies and true bugs. There is extreme variation in gall morphology, as seen in this images below:

Sawfly gall

Eurosta fly gall

Ocellate gall midge

Gall hat made by George Melika at the International Congress of Hymenopterists in Hungary, 2010

Galls provide nutrition to developing larvae and offer microclimate protection. Some gall inducing stimuli are saliva, maternal secretions, and larval secretions. They have complex external structures, and the mechanisms of how insects make galls and influence the plant’s response is still lagely unknown! Frederik Ronquist calls this the Holy Grail of science! We are hoping someone discovers how the fascinating structures are formed soon.

The next insect products discussed were wasp nests. Their external surfaces can range from smooth to spiky, and they can be constructed from mud, paper, etc. Mud wasps (sphecids, crabronids, etc.) and potter wasps (Vespidae) construct nests from mud and regurgitated water. It is thought that native Americans modeled their pottery after potter wasps nests!! Seeing this image, this isn’t too hard to imagine.

Mud wasp nest

Oothecae are another evolutionary marvel produced by a few types in insect, including cockroaches, which construct their ootheca from calcium oxalate, proteins, uric acid and water, and mantids, which construct theirs from calcium citrate. The ootheca helps protect eggs from predators, microclimate, etc.

We then discussed bees wax, honeybee nests, and some crafty megachilids (leaf cutter bees) that use mud and pebbles to help camouflage their nests into rocksides (see image below). Some megachilids roll cut sections of leaves together and cut a small circle out of a leaf to seal the opening. Some Osmia bees use flower petals instead of leaves to construct the nest!

Osmia nests constructed of flower petals

These amazing insect products made us wonder… could the product itself (like a nest, gall, or ootheca) be considered a part of an insect’s morphology? In ENT 502, we defined morphology as something that has a “form” and a “function”, and morphology is NOT the same as anatomy. Since some insect products can be diagnostic characters (and morphological characters can be diagnostic), can they be considered morphological characters? Or are they ecological characters? A tool has a form and a function though, so does that mean that a stick held by a monkey and used as a hammer could be consider part of the morphology of the monkey? Or a more realistic example – could the nest of a paper wasp be considered part of the wasp’s morphology? What do you think?