Small World


Head of a male Culex pipiens mosquito
Image: Gareth Paul Jones
2013 Small World Image of Distinction

The end of October approaches and that means winners of the 2014 Nikon Small World Photomicroscopy Contest will be announced. Every year, several images of insects and other arthropods compete (my favorites). The contest showcases microscopic techneques. Stacking is commonly used in insect images. Stacking corrects for the fact that 3D images viewed under the microscope always have regions that are out of focus because they are above or below the focus of the lens. To correct the focus, a series of images is collected by lowering the plane of focus in small increments to produce a “stack”. Each image in the stack has regions in focus and not in focus. Computer software merges the regions that are in focus to produce a composite image with all the parts in focus. This techniques overcomes the depth of field problems that lead to image distortion and produces beautiful images.
The deadline for 2015 is April 30, 2015.

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Producing the Proboscis

Butterfly Proboscis

Butterfly Proboscis
Image: Stephen Nagy, Nikon Small World

The proboscis of the butterfly is formed during the pupa stage. The lobes (galea) of the maxillae (middle mouthparts) extend and are formed as two separate half tubes. When the butterfly emerges from its chrysalis, each half of the proboscis is drawn out separately. Each half coils and the coils may become entangled. The butterfly contracts the muscles at the base and the half tubes extend. As the coiling and uncoiling of the mouthparts is repeated, the two halves align to form a single tube starting from the base of the mouthpart. Fluid released from the mouth causes the two halves to more strongly adhere and create a tube through which more liquid can travel down the tube. Ventrally, each half has “hooks” that interlock in a tongue and groove fashion. The dorsal side of the proboscis has plates that overlap.

The tightly opposed halves are then made into a tight coil such that each part of the inner coils is held in place by the coil above and below. The unlinked portions of the tube are coiled and uncoiled until they press together. Anti-paralel movements of the two halves properly align all hooks and plates. The proper alignment of the mouthpart halves takes between 30 minutes and 4 hours. After the cuticle hardens, the mouthparts cannot be easily separated. They are hardened in place. If linkage has not occurred before the cuticle hardens, the halves cannot be linked nor can a proboscis that is forced apart re-link properly. It is an odd way to make a feeding tube, but it works for butterflies.

Posted in behavior, Biomaterials, by jjneal, Taxonomy | 1 Comment

Why DEET Repels Mosquitoes



The mosquito repellent DEET was discovered by testing large numbers of chemicals for mosquito repellent properties. Why it is effective was not understood until many years later. DEET is known to interact with olfactory receptors in the mosquito antenna and disrupt their signalling. Current thought is that mosquitoes rely on olfactory stimuli to guide their feeding behavior. DEET disrupts the olfactory nerves, sending a confusing set of signals to the mosquito brain. Lacking the proper set of stimuli to induce biting and feeding, the confused mosquito flies off without a blood meal.

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Butterfly Proboscis

Checkered Skipper

Checkered Skipper

The butterfly proboscis (feeding tube) is a cellular structure that is covered with cuticle. The cuticle contains the protein resilin, one of the most elastic proteins investigated. The proboscis can be stretched by the contration of muscles in the base of the proboscis that cause it to extend. Some Lepidotera can hyper-extend the tip so that it has a slight upward bend. This bend makes it easier for the butterfly to insert it deep into flowers to retrieve nectar.

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Beetle Brunch

beetle pancake

Beetle Pancake
Artist: Nathan Shields
ScreenShot; YouTube

When I was little, my mother would make pancakes on Sunday morning. Bunny Pancakes with ears and a tail were a big hit. Why settle for bunnies when you can make beetles? Artist Nathan Shields demonstrates in the YouTube Video below. The click beetle is especially awesome.

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A Matter of Taste

Fruit Flies

Drosophila Flies

Efforts to understand nervous systems and basic functions such as taste discrimination often turn to insects that have systems that can be more readily explored and manipulated. Drosophila melanogaster has taste receptors in both its mouthparts and on the ends of its legs (tarsi). Mutations can be produced in Drosophila that allow exploration at the genetic and molecular level. Combined with neurological techniques, Drosophila is a powerful model to explore how a taste system functions.

Drosophila has 6 classes of taste receptors on its tarsi, based on response to sugar/sweet/sour/bitter. Flies walking on potential food items receive information about the quality. Using the legs to taste is more efficient than using the mouthparts would be.

Receptors on the prothoracic (front) legs differ in quality from receptors on the mouthparts and the metathoracic (middle) legs. The receptors on the mouthparts only contact the food after the information from the leg receptors have convinced the fly to begin feeding. Apparently the fly needs different information about the food it is eating than it needs to make its decision to eat. The differences in taste receptors in different locations on the fly provide a means to connect the function of the receptors with fly behavior.

Taste reception has components in common in all animals. What we learn from fruit flies can be used to better understand our own sense of taste.

Time flies like an arrow.
Fruit flies like a banana.

The Journal of Neuroscience, 21 May 2014, 34(21): 7148-7164
doi: 10.1523/JNEUROSCI.0649-14.2014

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Friday Cat-erpillar Blogging: Silkworm Sex Determination


Silkworm, Bombyx mori

Insects have a variety of systems for determining male and female. Some like the Drosophila Fly, Drosophila melanogaster, have an XY system similar to humans: Females have two copies of an X chromosome (XX), Males have one X and one Y chromosome (XY). A similar sex determination system makes Drosophila an even more useful model for human genetics. The silkworm sex determination system has been an enigma. Like some reptiles and birds, silkworms have a ZW sex determination system. Males are ZZ and Females are ZW. A factor on the W chromosome, when present, produces females, but identifying that factor has been elusive. The silkworm W chromosome lacks DNA sequences that encode proteins. Instead, the DNA produces RNA that interacts with proteins (pi-RNA).

One such RNA produced by the W chromosome, named “Fem” is the precursor of an RNA that silences the Masc gene. The Masc gene produces a protein causes the insect to express male features. A male silkworm with two Z chromosomes (ZZ) produces the Masc proteins and has male features. A female silkworm has a W chromosome that produces Fem and silences the Masc gene on the Z chromosome. A female produces very little Masc protein and has female features. Comparisons of sex determination in different species leads to a deeper understanding of the sex determination process in all species.

Read More: A single female-specific piRNA is the primary determiner of sex in the silkworm. Takashi Kiuchi, Hikaru Koga, Munetaka Kawamoto, Keisuke Shoji, Hiroki Sakai, Yuji Arai, Genki Ishihara, Shinpei Kawaoka, Sumio Sugano, Toru Shimada, Yutaka Suzuki, Masataka G. Suzuki & Susumu Katsuma. 2014. Nature 509: 633–636

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