Author Archive

Insect of the week – number 102

Friday, December 30th, 2011

Insect of the week – number 88

Friday, September 9th, 2011

Female of Megischus bicolor sickmanni

Exploring new methods of visualization

Thursday, July 7th, 2011

Describing morphological structures, especially when working with extremely small specimens, can be a difficult and often frustrating endeavor. The most difficult part is visualizing three dimensional structures.

What is the best imaging method?

The answer is not trivial. There is no one method that we can use for all structures. There are various methods of imaging we can utilize, whether we want to see surface sculptures, relative position of structures, muscles, or any other structure we might need to visualize. Scanning electron microscopy is excellent for examining surface sculpture, but we cannot see past the surface of a structure, nor can we see color with this method. Bright field microscopy using a stereo or compound microscope allows us to see color, and using transmitted light, we can see through transparent structures. Using laser scanning confocal imagery, we can highlight various materials by causing them to fluoresce at different wavelengths, which we can display in different colors. This allows us to see the limits of different materials such as muscles and sclerites. The point of imaging a structure is to help us visualize a structure but it is also to help us describe structures to others, because a picture is worth a thousand words.

In the Deans lab we have recently explored some methods for visualization that allow us to see the shape and relative position of structures. Images have been produced of the ovipositor structure of Trassedia luapi (Hymenoptera: Megaspilidae) using both bright field microscopy and laser scanning confocal microscopy. The ovipositor is the structure that a female uses to lay eggs on or in her host. The ovipositor of Trassedia luapi is only about 1.5mm long. Because of the high magnification we use to view such small structures, the range of focus is extremely narrow. To account for this, images are taken at several planes of focus. Using the appropriate software, the series of images are used to build a single image where all parts of the structure are in focus. This is an excellent method for visualizing a three dimensional structure, however it can be difficult to determine the arrangement of structures on top of one another. Using the same set of images, we can create videos that move progressively through the set of images. This visualization technique gives us a perspective of depth. With laser scanning confocal images, we can also produce a rotating three dimensional model of the structure.

Trassedia luapi ovipositor, bright field montage

Trassedia luapi ovipositor, laser scanning confocal montage

Insect of the week – number 75

Friday, June 10th, 2011
Image of Gomphus exilis, taken by Jeffrey S. Pippen.

Insect of the week – number 61

Friday, March 4th, 2011

Insect of the week – number 35

Friday, September 3rd, 2010

Siphonaptera: Pulicidae: Ctenocephalides canis (Curtis)

Ctenocephalides canis, dog flea

In contrast to our last insect of the week, this insect is no friend to people or to “man’s best friend”. This insect is more commonly known as the dog flea. Through the summer many dog owners notice their pets scratching relentlessly in the attempt to rid themselves of these little insects with their sharp piercing mouthparts.

Fleas are holometabolous which means they have complete metamorphosis. The adults ingest a great deal of blood to obtain the nutrients they need, while defecating all the excess other nutrients they don’t need. The defecation is in the form of dark brown pellets often referred to as flea dirt. This flea dirt, as well as other organic debris makes up the primary sustenance of the larvae. That’s right, the larvae eat their parents’ poo. This odd lifestyle is made possible by the fact that most mammals and birds have a nest or bedding area where they sleep and rear their young. The nest or bedding area becomes a perfect place for flea dirt to accumulate, as well as hosts for the fleas to inhabit after pupation.

Fleas are well known for their jumping abilities. Behind the hind legs of adult fleas, there is a pad made up of an extremely elastic protein called resilin. The flea compresses this elastic pad, storing energy. When released this stored energy flings the insect into the air, up to 50cm (Cadiergues 2000).

The dog flea is the intermediate host of the dog tapeworm Dipylidium caninum which can infect humans as well. Tapeworms are gut parasites that release eggs into its host’s feces. The larvae of fleas, as they eat what organic debris is available, may ingest some of these eggs. The tapeworms will partially develop in the flea as it matures. When the flea is an adult, the tapeworm passes out with the flea’s feces, where it might be ingested by a dog as it bites and nibbles after the annoying fleas. If the infected flea feces were somehow ingested by a human, it would develop just as it would in a dog.

Other fleas, such as the rodent fleas can transmit diseases organisms such as Yersinia pestis, also known as plague.

Our museum collection has 370 identified and slide mounted specimens, All collected from 1925-1940, most from the early 1930’s, and 3 vials in our alcohol preserved specimens, none collected recently. Collection localities range through several counties in North Carolina; Wake, Orange, Wilkes, and McDowell counties were prominent collecting sites.

Ctenocephalides canis records on GBIF – 98
http://data.gbif.org/species/14232735/

Find out more:

Cadiergues, M.-C., C. Joubert, et al. (2000). “A comparison of jump performances of the dog flea, Ctenocephalides canis (Curtis, 1826) and the cat flea, Ctenocephalides felis felis (Bouché, 1835).” Veterinary Parasitology 92(3): 239-241.

Pictoral Keys to fleas:
www.cdc.gov/nceh/ehs/Docs/Pictorial_Keys/Fleas.pdf

CDC Division of Vector-Borne Infectious Diseases
http://www.cdc.gov/ncidod/dvbid/plague/info.htm