(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.
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!