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.

Posted in behavior, by jjneal, Pest Management | Leave a comment

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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Walking On the Ceiling

Microscopy of a blow fly tarsus Left:  Terminal Tarsal Segment showing Claw and pulvilli (p)  Middle:  Tenant hairs of the pulvil magnified Right:  Higher magnification of a spatulate tip of a tenant hair. Image: Walker & Colleagues*

Microscopy of a blow fly tarsus
Left: Terminal Tarsal Segment showing Claw and pulvilli (p)
Middle: Tenant hairs of the pulvil magnified
Right: Higher magnification of a spatulate tip of a tenant hair.
Image: Walker & Colleagues*

Flies are noted for their ability to land and attach to smooth surfaces such as glass. The pads or pulvilli (p) on the ends of the legs give the fly its grip. Pulvilli have rows of tenant hairs with a spatulate tip, lubricated with a lipid. When pressed against a surface, the lipid creates a strong grip between the spatulate tips of the hairs and the surface. Flies walking on glass will leave tiny droplets of lipid (fly specks) where they walk.

G. WALKER, A.B. YULEAND, J. RATCLIFFE. 1985. The adhesive organ of the blowfly, Calliphora vomitoria:
a functional approach (Diptera: Calliphoridae). J. Zool., Lond. ( A ) 205:297-307

Posted in behavior, by jjneal, Taxonomy | Leave a comment

Blow Fly Lighting

Blow Fly Eyes

Blow Fly Eyes
Top: Under Normal Light Before Fluorescent Coating
Bottom Under UV Light After Fluorescent Coating
Image: Appl. Phys. Lett. 105, 103703 (2014)

Blow fly compound eyes are adapted to receiving light from a wide field of view. The arrangement is a model for man-made wide field sensors. Can an eye that receives light from a wide angle be used to transmit light in a wide angle?

To test this, a group of engineers* removed the corneal lenses of blow flies, mounted them on brass and coated them with a fluorescent material. They excited the coating with UV light and measured the directional intensity of emission. Compared to a flat surface, the coated blow fly eye illuminated a wide angle much more uniformly.

Money Quotes:

Disgusted even though most people are with flies, we do not advocate the mass harvesting of flies to obtain corneas to make light sources of the kind we have investigated. Instead, an industrially scalable bioreplication technique can be used to make multiple replicas of just a few corneas, and the replicas can be coated with one or more fluorescent materials.*


We hope that our initial demonstration will pave the way for the development of bioreplicated light-emitting and light-detecting photonic devices.*

*Raúl J. Martín-Palma1, Amy E. Miller, Drew P. Pulsifer and Akhlesh Lakhtakia. (2014) Angular distribution of light emission from compound-eye cornea with conformal fluorescent coating. Appl. Phys. Lett. 105:103703.


Posted in Biomaterials, by jjneal, Taxonomy | Leave a comment