Wednesday, August 31, 2011

Tobacco Hornworm (Manduca sexta) and the Parasite Wasp (Cotesia spp.)


The picture on the left is the tobacco hornworm (Manduca sexta) that infested my tomato plant.  The insect belong to Sphingidae family, commonly known as hawk moth.  The tobacco hornworms can be distinguished from the closely related tomato hornworms by their seven diagonal stripes versus eight v-shaped marking on the tomato hornworms.  The most striking feature of the hornworm is the thick pointing structure (or horn) located dorsally on the terminal abdominal segment.  On the back of the larvae, there are clusters of parasite wasp cocoons which has be infested the larvae and emerge from the skeleton.

This post, I am getting some close-up view of the tobacco hornworm and the parasite wasps under a stereo microscope.

Close-up of the tobacco hornworm

Mandible of the larvae (slightly out-of-focus are the thoracic legs)
Thoracic legs
The tip of the prolegs on abdomen.  Now, you know why it is so hard to remove the caterpillar from the tomato vine.  They are full of “claws”.
Another view of the spiracle (with 4x objective rather than 2x)
The spiracles and the lesions caused by the parasite wasps
The terminal segment of the abdomen.  The end is full of spikes.  That’s how they stick to the vine when you are trying to pull them off the vine.
The horn - “signature” of the tobacco hornworm.

The parasite Wasp

Day3 (8/29/2011): The cocoons of the parasite wasp at the dorsal of the tobacco hornworm (this picture was taken about 48 hour after we collected the hornworm)
Cut open the cocoon, there was a larvae inside
Continue to peel open the cocoon.  Here’s full view of the larvae.
Day 4 (8/30/2011): Just one day after I opened up the cocoon.  Apparently there was a big change inside of the larvae.  It’s already taking the shape of the wasp and with legs and pigmented eyes developed.
Day 5 (8/31/2011): Start to show darker pigmentation
Day 6 (9/1/2011): Even Darker pigmentation.  Still no movement
Day7 (9/2/2011): The appendages and antennas are starting to extend out and show some movement.  Occasionally, it would tweet its legs or antenna.  Wings are more visible now.
The wasp starting out with cutting a ring close to the top of the cocoon.
It did not cut all the way through.  It started to push when it the cut was about 90 percent of the circumference.
Continue to push.  First the antenna then the two front legs.
cotesia_cocoon_completely_came_off Finally, completely came out of the cocoon.


wasp_stichThe wasp that was removed from the cocoon did not survive.  Its wing did not extended out fully.  The picture on the left was another wasp that came out of cocoon on the same date. The pictures were combined using Microsoft image composite Editor since the antenna are very long and extended out of the field of view.

cotesia_top cotesia_bottom


Video recording of the parasite wasp come out of the cocoon

Sunday, August 14, 2011

Sand from Thermal City Gold Mine

Returning from Thermal City Gold mine yesterday and spending most of the day learning how to get rich from panning gold.  The science behind of gold panning is based on the gold density.  After stirring up the gold containing sand, the heavier gold will sink to the bottom while other materials will stay on the top.   The process involved in continuous removal of lighter sand on the top and eventually the heavier gold will become more concentrated.  I heard from staff there are plenty of microscopic gold in the sediment.  I brought home a bag of sand from the last stage of panning which contains plenty of black sands (Magnetite) and hopefully some microscopic gold in there.


Figure 1 The remaining sand of the last step of gold panning process contains very high percentage of black sand.  Many of the black sands are in fact Magnetite, an ferromagnetic mineral with chemical formula of Fe3O4.  Some green colored crystals are olivine, an magnesium iron silicate with the formula of (Mg,Fe)2SiO4.  I suspect the the pink colored crystals are rubies which are also found in the area.  Of course, the majority of the colorless crystals are quartz which is the most common mineral in the sand.


Figure 2 WE FOUND GOLD!! These are the two pieces I found in my last pan.  It would have been such a big disappointment without finding any gold during the field trip.  The length of the gold is about 1mm.  That’s the size that most of us found.  Some of the folds do find some flakes about 3-4 mm.


Figure 3 A piece a mica in the sand.  Lots of people mistake these as gold due to their metallic reflection.  They can be easily distinguished from gold because they change the reflection when looked from different angle.

Wednesday, August 10, 2011

Contrast enhancement for plant cell viewing

It’s difficult to see cells under a regular brightfield microscope when they don’t have pigment or stained with color.  The reason is that the light source of a brightfield microscope was placed directly underneath the specimen.  The light penetrate the specimen to illuminate the specimen and finally reach your retina.  There is very little deflection of the light to create the contrast.  Some simple filters can be added to the optical train to create the contrast.


Figure 1.  Onion epidermis cell under regular brightfield microscope.

Onion_DarkField DarkField


Figure 2.  adding a darkfield filter to the light path, the cell wall can be easier to see.

Onion_Rheinberg_two_color Rheinberg

Figure 3. Based on the darkfield technique,  The Rheinberg illumination, a form a optical staining, can stain the specimen without chemical stain.  The method used a color filter consists of two or more colors to allow the light with different color come from different direction which create the structure to be “Stained” with different color.  The above image was viewed under a Rheinberg filter with green center and red peripheral.


Figure 4. Of course, it is inevitable to use chemical staining if the structure of interest has very different chemical composition but very little in deflecting light.  The above picture is an onion epidermis cell with the nucleus in the center.  The specimen was stained with Methylene blue.  The nucleus was darker because methylene blue has stronger binding to nucleic acid than cytoplasm.

The steps for making the filters was described earlier at Laboratory and Home Science Resources.


Saturday, August 6, 2011

Ibuprofen Crystal Growing Habit in Different Solvents

The microcrystalline test is a procedure used by the scientists to identify the substances with birefringent property. The scientist adds a drop of the suspected substance to a chemical on a slide. The mixture will begin to form crystals. Each type of drug has an individual crystal pattern when seen under a polarized light microscope (PLM).
I was cleaning up my medicine cabinet and found a bottle of expired ibuprofen. Instead of throwing it away, I decided to try it out under PLM. The medicine has brown coating, it was easily removed by rinse off with water. The interior is crystal white. I dissolved one pill in water and another one in 95% Ethanol.  The solution was left overnight get it as close to as saturation as possible.
Ibuprofen formed in water

Ibuprofen formed in water

Ibuprofen formed in ethanol

Ibuprofen formed in ethanol
The ibuprofen crystals formed in water showed more compact form than the crystals formed in ethanol. The crystals formed in ethanol have feather like shape and less compact.  Here is my explanation: Compared to water, ethanol has less surface tension so they spread out quickly so it has larger surface area.  In addition to having larger surface area, ethanol also has lower boiling point so it evaporate quickly.  Ibuprofen has less chance to form compact and organized crystals.

Thursday, July 28, 2011

Making whole insect slide – an easy way

In the previous post, I presented a modified method of microscope slide making originally described by Schauff.  The method involved four steps: maceration, cleaning, dehydration and mounting.  The process removes the non-transparent internal organs and preserves the chitin exoskeleton.  It allows the clear viewing the minute details of insects at high magnification using a compound microscope.  It does has draw backs, including the use of caustic reagents and the potential of damaging the specimen using picks for cleaning.  Sometime, you may not need to observe them in high magnification and wanted to preserve their natural shape.  I came across a website (forgot to bookmark it.  I lose the link and can’t seem to find it back.) which directly mounted the insects stored in alcohol.  The protocol used Xylene and Canada balsam.  I decided again using the less toxic alcohol and nail polish top coat.


The first stop is to build a shallow well to create space so that the insects won’t be crushed by the slide and maintained the natural shape.  I found the electronic plastic package material will serve me well for this purpose.  The thickness is about 0.5mm.  It’s not too deep that I had to fill in lots of mountant but not too shallow to allow the cover slip to crush the insect.  It’s hard enough to maintain the shape but soft enough to cut with a pair of scissor.

hole_puncherThe first step was to cut a piece of plastic to the size slightly smaller than the slide but larger than the cover slip. The next is to make some holes with hole puncher – can be purchased from regular office supply store.  Apply some finger nail top coat on one side of the plastic.  Glue it to the slide and wait until it dried.  Pick up the insects from the preservation alcohol then transfers them to the well with a pair of tweezers.  Use the pick to adjust the body orientation and appendages to show their natural position.  Put a few drops of finger nail polish top coat in each well until it slightly over the top of the plastic.  Care should be taken to ensure that no bubble is introduced into the mountant.  Any bubble introduced into the mountant will be enlarged after the mountant dried out.aphid_under800






An aphid nymph was mounted upside down to show the under side of the insect.








An aphid nymph top view








Wing adult aphid

This post, I presented an easy method for mounting insect onto microscope slide. The method is not appropriate for view the insect at high magnification for certain non-transparent body parts but it is appropriate for the viewing at low magnification with a stereo microscope using the top light.